-#^ ^ * 
 
 m 
 
ELEMENTARY EXPERIMENTS 
 
 IN 
 
 PSYCHOLOGY 
 
 BY 
 
 CARL E. SEASHORE 
 
 W 
 Bead of the Department of Philosophy and Psychology and Bean of the 
 
 Graduate College in the State University of Iowa 
 
 NEW YORK 
 HENRY HOLT AND COMPANY 
 
 1908 
 

 PSYCH. 
 LIBRARY 
 
 •HAL 
 
 Copyright, 1908, 
 
 BY 
 
 HENRY HOLT AND COMPANY 
 
 THE QUINN & BODEN CO. PRESS 
 RAHWAV, N. J. 
 
PEEFACE 
 
 This manual is designed to meet the requirements 
 for a series of individual experiments in the first course 
 in psychology. It makes individual experiments, as 
 opposed to class demonstrations, practicable, regardless 
 of laboratory facilities or the size of the class. The 
 student is given means and encouragement for pursuing 
 each problem intensively in order that he may acquire 
 independence of thought and action, realize the actual- 
 ity of mental processes, and get here and there a vision 
 of the vastness, the orderliness, the practical signifi- 
 cance, and the charms of mental life. 
 
 'No laboratory facilities are required. In this there 
 is a triple gain : it saves the manifolding of equipment, 
 it frees the student from the technicalities incidental 
 to the manipulation of apparatus at a time when his 
 energies need to be conserved for the grasping of the 
 psychological problem, and it saves time for the class 
 period, the experiments being adapted for outside as- 
 signments. The apparatus other than that ordinarily 
 at the disposal of students is supplied with the book in 
 the accompanying envelope.* 
 
 * The president of a college asked a distinguished psychologist 
 how much money his board ought to appropriate for the equip- 
 ment of a fair elementary laboratory. The reply came: "Three 
 thousand dollars a year for a good instructor and one dollar 
 for paper and pins." This manual supplies the paper and pins 
 and, in part, the instructor. 
 
 iii 
 
 178214 
 
iv PEEFACE 
 
 The experiments are independent and self-explana- 
 tory. Provided the manual is used in connection with 
 the customary elementary text-book or lectures, the 
 experiments require no introduction ; the directions are 
 adequate, and the running comment furnishes the set- 
 ting for each step and enables the student to see the 
 significance of the results. The beginner needs much 
 help in his experiments in psychology, and there is no 
 more practical way of giving it than through a manual. 
 
 This is not a laboratory manual. It is a manual of 
 experiments which the student should perform before 
 he is admitted to the laboratory, or in case he does not 
 intend to pursue the subject beyond one course. It is 
 not a text-book by itself, but a supplement to any good 
 text-book. It does not review the field of psychology, but 
 simply furnishes the intensive, individual, experimental 
 part of the instruction. It does not furnish technical in- 
 struction on methods of experimenting, but, like the 
 conversational method of teaching language, everywhere 
 encourages right procedure. It does not purport to 
 cover the most important matters ; sometimes an almost 
 insignificant topic (for example, the subject of the first 
 chapter) is chosen for the purpose of deepening insight. 
 It by no means supplants the class demonstrations and 
 experiments, except in the few topics selected, and even 
 here the instructor may profitably supplement and show 
 how the same experiments may be performed by the 
 usual laboratory apparatus. 
 
 The manual presupposes such knowledge of the nerv- 
 ous system ^s is imparted by the text-books most used in 
 psychology. It aims to retain the most generally ac- 
 
PREFACE V 
 
 cepted classifications and terms, to introduce those ex- 
 p.eriments which have come into most general favor, 
 and to leave untouched those fields in which experiment 
 has been of doubtful value. The discussion on each 
 topic is limited to the bearings of the experiment. 
 
 As to the method of using the book, each instructor 
 will naturally adopt that best suited to his situation. 
 If space is available, the students should be encouraged 
 to perform the experiments in the roojns of the depart- 
 ment during certain open hours, and under the general 
 supervision of an assistant. There should be sufficient 
 time allowed in the recitation-period for special sug- 
 gestions and directions to the students, and for reports 
 upon the completed experiment. The students' notes 
 on each topic must be collected and checked rigorously ; 
 for, no matter how explicit the directions may be, the 
 quality of the work must be passed upon by the instruc- 
 tor. It is profitable to require the students to take 
 turns in working over the reports to show difficulties, 
 original observations, special demonstrations, etc. Or- 
 dinarily each experiment will take two hours. The 
 first experiment should be divided into two assignments, 
 on account of the newness of the work and in order 
 to avoid fatigue. 
 
 Titchener's monumental four-volume set of labora- 
 tory manuals is a most valuable compendium.* It 
 contains bibliographies, besides technical discussions of 
 nearly every topic in this course. Sanford's,t Wit- 
 
 *Titehener, "Experimental Psychology": Qualitative (I) Stu- 
 dent's Manual and (II) Instructor's Manual; Quantitative '(III) 
 Student's Manual and (IV) Instructor's Manual. 
 
 f Sanford, "Experimental Psychology." 
 
vi PREFACE 
 
 mer's,* and Judd'st manuals are helpful references. 
 Baldwin's dictionary of Philosophy and Psychology 
 should also be on the reference-table, together with the 
 most approved elementary texts. 
 
 The author has gleaned material from many sources 
 and wishes here to acknowledge his gTateful obligations 
 to those who find themselves contributors to this volume. 
 He has had the benefit of helpful advice from many 
 psychologists of experience ; several of them have kindly 
 read the manuscript and made valuable suggestions. 
 He is especially indebted to his colleague Dr. Mabel 
 Clare Williams for cooperation. 
 
 *Witmer, "Analytical Psychologj\" 
 
 f Judd, "Laboratory Manual of Psychology" and "Laboratory 
 Equipment for Psychological Experiments." 
 
CONTENTS 
 
 Preface 
 Introduction 
 I. Visual After-Images 
 II. Visual Contrast 
 
 III. The Visual Field 
 
 IV. Visual Space 
 
 V. Auditory Space . 
 VI. Tactual Space 
 VII. Cutaneous Sensations 
 VIII. Weber's Law 
 IX. Mental Images . 
 X. -Association . 
 XI. ' Memory .^ . 
 XII. Apperception 
 
 XIII. Attention 
 
 XIV. NoRMAX Illusions 
 XV. Affective Tone . 
 
 XVI. Reaction-Time 
 
 PAGE 
 
 iii 
 
 ix 
 
 1 
 
 13 
 
 23 
 
 39 
 
 55 
 
 71 
 
 82 
 
 91 
 
 104 
 
 118 
 
 131 
 
 144 
 
 158 
 
 172 
 
 191 
 
 205 
 
 vii 
 
INTEODUCTIOK 
 
 To the Student: 
 
 Psychology is a systematic study of mental life. 
 You now turn from the study of physical forces, rocks, 
 flowers, and animal tissues, in nature without, to a study 
 of your own mind. You are to perform experiments 
 upon yourself. 
 
 The experimental method enables you to analyze and 
 reduce a mental process to its simplest elements; to 
 control, repeat, and vary the conditions systematically; 
 to record the results; to trace interrelations and ex- 
 planations of known phenomena; and to discover new 
 facts and problems. 
 
 This manual is so arranged as to furnish set exer- 
 cises in which directions, aids, and explanations are 
 given in the order needed. Onl}^ a few of the most 
 general suggestions for your guidance need be given 
 here. 
 
 Finish as you go along. The paragraph is the unit ; 
 always read a paragraph at a time and perform the 
 experiment, write the report, or master the explanation 
 before you read the next. This is mandatory, because 
 glancing ahead would often vitiate the experiment. 
 
 Take systematic notes. The directions for notes are 
 specific in certain minimum requirements. These notes 
 are not primarily for the information of the instructor, 
 or for reviews and examinations, but for the purpose 
 
X INTRODUCTION 
 
 of clinching the observed facts and gaining practice in 
 the recording of the results, which is an essential step in 
 an experiment. Use loose-leaf note-books ; hand in the 
 report for each experiment to the instructor for inspec- 
 tion ; and file the notes as they are returned. 
 
 Work intensively. Seek the most thorough insight 
 into the problem under consideration ; note new observa- 
 tions, test ideas suggested to you, verify and check as 
 much as time permits. Reason, and thus develop con- 
 fidence in your own judgment and power of observation. 
 But always adhere to the set tojoic. Do not ramble, or 
 follow up the countless fascinating side lines which 
 come to view. Follow the directions closely, then 
 develop your original ideas. 
 
 Apply what you learn. You will learn, for example, 
 many laws of mental economy in this course. When 
 you have discovered and demonstrated such laws, use 
 them. Economize mental energy ! Psychologize in 
 your history lesson, your literature, your material 
 science, your athletics, — wherever you are concerned 
 with mental processes. To educate, to heal, to govern, 
 to please, to interpret the efforts and j)roducts of the 
 human mind; to understand inclinations, proclivities, 
 and capacities of your own and other minds, involves 
 knowdedge of mind, which is psychology."^ 
 
 * "Only with the aid of psychology can one to the fullest 
 possible extent reap the benefits of the study of other forms 
 of science. Language cannot be understood, literature cannot 
 be appreciated, read, and interpreted, art cannot be profoundly 
 comprehended, and even the natural sciences cannot have their 
 full import revealed, without a knowledge of the mind of man. 
 And, indeed, how could this be otlierwise, since all science itself 
 is only the product of the human mind?" (Ladd.) 
 
INTRODUCTION xi 
 
 Be impartial: be not self-centered. You will be 
 called upon to exhibit and measure your mental capaci- 
 ties in various ways, and it requires the integrity and 
 courage of a scientist to observe and report these with- 
 out bias. 
 
 Go only as far in an assignment as you can go thor- 
 oughly. One student may be able to proceed two or 
 three times as fast as another. If you find that the 
 lesson is too long for you, do not skim over any part, 
 but proceed as far as you can and record the time limit. 
 
 In the experiments that follow, 'Tor one" means that 
 the experiments so headed may be performed by one 
 person alone. 'Tor two" means that two must work 
 together, one acting as experimenter (E) and the other 
 as observer (O). Shift in each experiment so that 
 each one may serve in turn both as experimenter and 
 as observer. Record which one served as observer first. 
 Each should keep the notes which naturally go into his 
 book according to the directions. Record also the date, 
 the hour of the beginning of the experiment, interrup- 
 tions, and any general conditions which might influence 
 the results. Use terse language. 
 
 To experiment is to ask questions of nature. Do not 
 simply repeat the set questions of the book, but let them 
 open deeper and more serviceable inquiries into your 
 mental nature. Your primary aim in this course should 
 be, not to collect facts, but to acquire training. Carry 
 habits of introspection, precision, analysis, and natural 
 explanation into life and you will realize the force of 
 our motto : 'Not psychology, but to psychologize. 
 
CHAPTEE I 
 VISUAL AFTER-IMAGES 
 
 For One* 
 Most of us have observed that, if we look for a mo- 
 ment at a liglit as it is being turned out, we see an 
 image of it a while afterward. That image is an after- 
 image, or after-sensation. Such images manifest them- 
 selves according to traceable laws and play an im- 
 portant, though seldom recog-nized, role in our experi- 
 ence. We shall now make a study of some of their 
 characteristic modes of behavior. 
 
 Success in this experiment depends mainly upon 
 concentration of attention and economy in the use of 
 the eyes. The eyes should not be allowed to wander 
 aimlessly over the figures, and it is well to close them 
 for rest as often as possible. Clear images can be 
 obtained only after steady fixation. It is easier to get 
 the after-image with one eye alone, but in the long run 
 it is more restful to use the two eyes together. 
 
 1. Existence, a. Brightness. — Place the black square 
 at the center of the upper half of a white sheet of 
 paper; fixate the center of it (i.e., look intently and 
 
 *Take from the envelope the large black and gray squares, and 
 the following small squares: black, gray, white, red, blue, yellow, 
 green, violet, and orange. Make a pinhole at the center of each 
 of these squares. ♦ 
 
 1 
 
2 VISUAL AFTEK-IMAGES 
 
 steadily at the pinhole) for about fifteen seconds ; "' then 
 look at the center of the lower half of the sheet of white 
 paper and you Avill see a bright square, which is the 
 after-image. Record your estimate of its relative size 
 and duration. 
 
 h. Color. — Try the red square in the same manner. 
 Record the color of the after-image. 
 
 An after-image is a sensory image which occurs as 
 the result of the stimulation of a sense-organ but 
 not until after the stimulus has been withdrawn. It 
 is a sort of echo and bears certain relations to the ob- 
 ject of which it is a copy as regards space, duration of 
 the primary impression, sense quality, and intensity. 
 Thus, in this experiment, you saw, on the surface of 
 the blank paper, copies of the squares possibly like the 
 original in every respect except brightnesst and color. 
 After-images combine certain characteristics of sensa- 
 tions and mental images and might equally well be 
 called after-sensations. 
 
 The causes of after-images are present in all our 
 vision and tend to modify practically all that we see. 
 Yet many persons live long and happily Avithout making 
 allowance for their distortions or even discovering the 
 existence of them. Every object that we see leaves an 
 impression which may bob up as an after-image, if suf- 
 ficiently strong and isolated. We look at a piece of 
 black paper and the next moment we see a copy 
 
 * A fixation-time of fifteen seconds is too long for some and 
 too short for other observers; each will soon determine what 
 time is most favorable for his eyes. 
 
 f Black, white, and all the intervening grays are called bright- 
 nesses. Brightness is also present in color. 
 
VISUAL AFTEE-IMAGES 3 
 
 of it wherever we cast our eyes ; the same is true about 
 a light, a color, an apple, a man, a tree, a book, a house — 
 any object which may impress the eye. The after- 
 images in themselves are not useful, and it is fortunate 
 that we have the instinctive power to disregard them 
 as effectively as we do. But even though we disregard 
 them, they modify our sensory experience and con- 
 tinually tone the colors, lights, and shades of our en- 
 vironment. 
 
 After-images occur in all the senses, but the visual 
 are the most consjDicuous. 
 
 2. Setting. — Eepeat Exp. 1 a and observe that, when 
 the light after-image appears, there is a change in the 
 white surface surrounding it.* Describe the change. 
 
 When we look at an object we may secure an after- 
 image not only of that object but also of its surround- 
 ings within a limited field of vision. This complexity 
 of the impression is one of the reasons why specific 
 after-images are so difficult to detect and so easy to 
 disregard. 
 
 After-images are local effects of the adaptation of 
 the eye to changes in brightness and color. When we 
 enter a dark room, it seems at first intensely dark, but 
 later it assumes gray or color effects. When we pass 
 from a dark into a light room, the light at first is daz- 
 zling, but the eye soon adapts itself so that after a 
 while the light does not seem so bright. During 
 adaptation all brightnesses and all colors tend toward 
 
 * If the white sheet is placed against a dark background, the 
 outline of the whole sheet may be seen in the after-image. 
 
4 VISUAL AFTER-IMAGES 
 
 gray. In the above experiment a square portion of the 
 retina is adapted to dark and the surrounding portion 
 to light. 
 
 3. Color. — In successive trials, produce after-images 
 of the five colors, blue, green, yellow, violet, and orange. 
 Record the dominating color in each after-image.* Cau 
 you formulate a law for this order of color? If so, 
 state it. 
 
 The after-image of any color goes through a series 
 of rapid changes, possibly covering the whole spectrum ; 
 but there is always one particular color which dom- 
 inates by being the most distinct and by persisting the 
 longest. This color is complementary to the color of the 
 stimulus, t Of course it is modified, according to cer- 
 tain laws, by the color and the brightness of the back- 
 ground upon which it is projected. 
 
 The after-image of the dark stimulus in the first 
 experiment was light; that is, antagonistic. We may 
 therefore combine the observations on brightness and 
 on color and say that the dominant color and brightness 
 of an after-image are antagonistic to the color and 
 brightness of the stimulus. All color after-images also 
 involve brightness-effects. Colors are often seen in the 
 after-images of non-colored objects. 
 
 4. Projection-background, a. Brightness-effect on 
 Brightness. — Repeat Exp. 1 a in six successive trials 
 
 * Do not try these in too rapid succession ; it may be well to 
 intersperse them with following experiments. Beware of look- 
 ing at the colors out of mere curiosity or aimlessness! 
 
 f Every color has a complementary, i.e., an opposite or antag- 
 onistic color. Colors are said to be complementary if they 
 neutralize each other and produce gray when mixed. 
 
VISUAL AFTER-IMAGES 6 
 
 under uniform conditions, except that you project the 
 image upon different backgrounds ; ^ namely, white, 
 gray, and black, in the double-fatigue order. f Record 
 the relative effectiveness of the three backgrounds. 
 
 The clearness of an image depends upon the bright- 
 ness-difference between it and its projection-back- 
 ground. When projected upon the white ground, in this 
 experiment, the light of the image is intensified and 
 the darkness of the surroundings is reduced by the 
 white; on the black ground, the light of the image is 
 minimized and the darkness of the surroundings is 
 enhanced by the black; while, on the gray, there is a 
 moderate interference with both image and surround- 
 ings. Hence brightness of the background makes com- 
 paratively little difference in the effectiveness of the 
 after-image, although the brightness of the three images 
 varies greatly. For a dark object the white projection- 
 background is, however, usually more effective, because 
 here the white enhances the image of the object itself, 
 whereas on a black projection-background it is the back- 
 ground of the object that is enhanced. 
 
 h. Brightness-effect on Color. — Repeat Exp. 1 & in 
 three successive trials, projecting the image upon white, 
 gray, and black backgrounds respectively. Record the 
 effect of the background upon the color of the after- 
 
 *Use the two large squares for gray and black projeetion-back- 
 grovmds. 
 
 ■f Double- fatigue order is the technical term for the giving of 
 a series of trials in one order and repeating them in the reverse 
 order; thus, white, gray, black; black, gray, white. The theory 
 is that such factors as fatigue and practice tend to even up by 
 this order. 
 
6 VISUAL AFTER-IMAGES 
 
 There is a distinct effect upon the brightness of the 
 color; the actual color of the image mixes with the 
 brightness of the background. 
 
 c. Color-effect on Color. — Project the after-image 
 of the red square, in successive trials, upon the yellow, 
 the blue, and the red square itself. Record the result- 
 ing color-effects. 
 
 The color of the after-image mixes with the color 
 of the background. Thus, the result on the yellow is a 
 greenish yellow; on the blue, a greenish blue; and on 
 the red a tendency toward gray. This last trial — red 
 upon red — explains why colors change and blur when 
 we look intently at them; the after-image of the red 
 disk is a pale green, and if it were projected upon a 
 pale red of the same strength, the result would be 
 to cancel both colors, according to the law of comple- 
 mentaries. 
 
 d. Absence of BacJcground. — Fixate the black square 
 as before, and then put your hands over your eyes and 
 you will see the image projected somewhere into space.* 
 Record your estimate of its size and distance and the 
 relative effectiveness of this and the foregoing modes of 
 projection. 
 
 The image may be projected anywhere — upon any 
 color or brightness, upon any form, at any distance 
 within sight. A glance at the setting sun produces 
 shifting color-effects upon the object we look at imme- 
 diately afterward ; the after-image of the green leaf in 
 
 * It is usually better to keep the eyes open when covered by 
 the hands; still, it makes but little difference whether they are 
 open or closed, provided the covering is adequate. 
 
VISUAL AFTEE-IMAGES 7 
 
 a woman's hat may be taken for a rosy blush upon 
 her cheek. 
 
 5. Negative and Positive. — Look at a lighted lamp * 
 for half a second, and then instantly cover the eyes and 
 observe the radical changes in color of the after-image. 
 Record the two dominant colors in the order of their 
 appearance, t 
 
 The positive after-image has the same relations of 
 brightness as the stimulus, as in a photographic positive. 
 The negative after-image has the relations of light 
 and shade reversed, as in the photographic negative. 
 The after-image may be of the same color as the 
 stimulus, or it may be other-colored. There are 
 positive same-colored and positive other-colored, nega- 
 tive same-colored and negative other-colored after- 
 images. Generally, however, positive after-images 
 are same-colored and negative other-colored are com- 
 plementary. 
 
 The positive after-image appears first and is usually 
 very short in duration and difficult to detect. To make 
 it conspicuous, one must employ a strong stimulus, as 
 in this experiment. After some training one may see 
 the positive after-image before the negative in the ex- 
 posure of ordinary objects of moderate intensity. 
 
 *Any kind: daylight does not interfere seriously. 
 
 •j- Positive after-images of brightness without color may be dem- 
 onstrated as follows: Face some distant object, as the branching 
 limb of a tree outlined against a clear sky; close the eyes and 
 cover with the hands for a minute; then open the hands and 
 eyes for a fraction of a second, and observe, immediately after 
 closing the eyes again, an image like the object in brightnesSc 
 This is the positive after-image. 
 
8 VISUAL AFTEK-IMAGES 
 
 6. Size and Distance. — In three successive trials 
 project an after-image of the black square, as in Exp. 1 a, 
 upon backgrounds at different distances from the eye ; 
 e.g., 1 ft., 3 ft., and 10 ft. Formulate a law of the 
 relation between size and distance. 
 
 This variation of the size with distance shows that 
 the after-image follows the same optical principles of 
 projection as the normal retinal image in perception. 
 
 7. Relief. — Project an after-image of a hat, a lamp- 
 globe, or any other object that presents relief or volume. 
 Is there any suggestion of relief or volume in the after- 
 image ? 
 
 The perception of relief depends upon the differences 
 between the images in the two eyes, delicate gradations 
 in brightness, and eye-movements, among other data. 
 The blurred edges, the reversal of brightness, and the 
 confusion of eye-muscle sensations militate against the 
 perceptions of relief in the after-image. Ordinarily 
 the after-image presents only the outline and does not 
 suggest relief, but training and care may enable one 
 to identify marks of relief. 
 
 8. Plasticity. — Project an after-image of the black 
 square into an upper corner of the room. Record 
 whether the image adapts itself to the ceiling and wall- 
 surfaces, or retains its flat form. 
 
 It may do either; which it shall do is a matter of 
 apperception. Usually it adapts itself plastically to the 
 surfaces. This is particularly true if the image is pro- 
 jected upon some familiar surface, as the sleeve or the 
 hand. 
 
VISUAL AFTEE-IMAGES 9 
 
 9. Movement. — Fixate the black square, as in Exp. 1 
 a, and project the image with eyes closed and covered 
 by the hands, and try to keep the after-image directly 
 before you. Does the image seem to move irresistibly ? 
 If so, in what direction ? 
 
 It is clear by this time that the after-image moves 
 mth the eyes ; with the eyes open, we see it in whatever 
 direction we look. But when the eyes are closed, and 
 we are not aware of their movement, most observers 
 find that the image has a curiously irresistible tendency 
 to move upward. 
 
 10. Latent Period, Duration, and Clearness. — In 
 
 each of the following four experiments record (1) the 
 approximate latent time,* (2) duration, and (3) rela- 
 tive clearness. 
 
 a. Time. — Project the after-image of the black 
 square first after a fixation of five seconds and then 
 after a fixation of ten seconds,t allowing due time for 
 recovery between the two. 
 
 h. Brightness. — Place the black and the gray squares 
 edge to edge upon the white sheet ; fixate the adjoining 
 edges and project the double image upon a white back- 
 ground. 
 
 c. Color. — Place the red, the green, the yellow, and 
 the blue squares in a cluster upon the white sheet ; mark 
 
 * The latent time of an after-image is the time which elapses 
 between the withdrawal of the stimulus and the beginning of 
 the appearance of the after-image. 
 
 f This time should be adapted to the individual needs, the 
 requirement being that a relatively short exposure-time shall be 
 compared with a longer one. 
 
10 VISUAL AFTER-IMAGES 
 
 a point in the center of the cluster; fixate the central 
 point and project the four-colored after-image upon a 
 white background. 
 
 d. Area. — Cut a piece of white paper about eight 
 millimeters square and place it and the white square 
 five millimeters apart upon the large black square ; fix- 
 ate a middle point and project the double image upon a 
 white backgi^ound.* 
 
 Long stimulation, large brightness-diiference between 
 the object and its background, and a moderately large 
 area are conducive to a short latent time, long duration, 
 and clearness of the after-image, t These laws are, 
 however, subject to numerous qualifications. 
 
 These experiments merely show how it is possible 
 to work out laws of the relation between stimuli and 
 after-images.:}: The rule is to study one factor at a time 
 and keep all other conditions constant. The factor 
 which is studied may be varied, as in the above separat- 
 ing of time, brightness, and area under controllable 
 conditions, and the effect of such variations may be 
 measured. 
 
 The certainty that the image shall appear depends 
 mainly upon the exposure-time, the area, and the bright- 
 ness of the stimulus, but also upon such subjective con- 
 ditions as are mentioned in the following paragTaph. 
 
 * A millimeter scale is printed on the last page of this book. 
 Fold the margin of that page so as to bring the scale marking 
 to the edge of the page. 
 
 f The variations with color are perhaps essentially due to the 
 difference in the brightness of the color. For this reason blue 
 is the most effective color in this group on a white background. 
 
 \ See Franz, "After-images," The Psychological Review Mono- 
 graph Supplement, Vol. Ill, No, 12. 
 
VISUAL AFTER-IMAGES 11 
 
 If any one of these is inadequate the image fails to 
 appear. As a rule, the after-image may be produced 
 if the object is presented utider such conditions as to 
 be clearly perceptible. Thus, an electric spark, which 
 endures only for an infinitesimal part of a second, may 
 produce an after-image ; in the present experiments the 
 observer may not have noticed the after-image of the 
 white seen through the pinhole, but objects of that size 
 may produce after-images under favorable conditions; 
 and one may not be able to get a distinct image of a 
 white plate upon a white tablecloth because the bright- 
 ness-difference is too small. 
 
 The duration of the after-image varies within wide 
 limits. In extreme cases the impression has been known 
 to persist for days and months, as with l^ewton, who 
 looked at the sun Avith his right eye and then saw the 
 sun continually before him for many days. The ordi- 
 nary duration is, however, limited to a few seconds, 
 and the image passes away gradually. In addition to 
 such objective conditions as exposure-time, area, and 
 brightness which we have noted, there are subjective 
 factors, such as practice, expectation, attention, etc., 
 which condition the duration. 
 
 11. Indirect Vision. — Fixate a point about seven 
 centimeters away from the center of the back square ; it 
 then stimulates the indirect field of the retina. Project 
 the after-image. Compare the effectiveness of this 
 image with the foregoing images from the direct field. 
 
 The best after-images are obtained from the center 
 of the retina. Clearness and duration gradually de- 
 
12 VISUAL AFTER-IMAGES 
 
 crease toAvard the periphery, and it is very difficult to 
 get any image from the extreme periphery of the retina. 
 In this respect the after-image behaves like the primary 
 image in perception. 
 
 12. Periodicity. — Fixate the black square nntil it 
 begins to blur and then project the after-image in the 
 most favorable way, and observe that it recurs again and 
 again. Record the number of appearances. 
 
 Under favorable circumstances the image may appear 
 twenty or thirty times. This periodic recurrence is 
 a fundamental law. Sometimes the usual sequence of 
 positive and negative phases may be observed in each 
 period. 
 
 The cause of after-images lies chiefly in the fact that, 
 as soon as a light stimulus ceases to act upon a given 
 portion of the retina, a reaction of the chemicallj^ antag- 
 onistic sort follows. The play of the after-image in all 
 its transitions through brightness and color follows the 
 course of this reaction in the retinal elements.* 
 
 * A good account of the principal plwsiological theories of 
 color-vision is found in Calkins, "Introduction to Psychology," 
 pp. 464-79. 
 
CHAPTER II 
 VISUAL CONTRAST 
 
 For One* 
 Every sensation is different from what it would have 
 been if it had been experienced together with, or in 
 sequence to, some other sensation. One of the best illus- 
 trations of this '^law of relativity" is to be found in 
 contrast, which we shall now study in the sense of 
 sight. 
 
 These experiments should be performed in good dif- 
 fused daylight. Unless otherwise directed, the object 
 must invariably be viewed through the tissue-paper. 
 The foregoing exercise has taught the importance of 
 avoiding fatigue for color and brightness. Make 
 prompt judgments and avoid unnecessary exposure of 
 the eyes to the figures. 
 
 1. Brightness-contrast. — Lay the black and the 
 white squares about three centimeters apart uj)on the 
 background; place a gray bar upon each of them and 
 cover the whole with the tissue-paper. Compare the 
 
 *Take all the small squares from the envelope. Cut two bars 
 from the small gray square and two from the pale green square 
 each 5 millimeters wide. Use tlie page at the end of the book 
 containing the millimeter scale for a background, and cover the 
 colors laid upon it with the facing sheet of tissue-paper. 
 
 13 
 
14 VISUAL CONTRAST 
 
 brightness of the two gray bars and record which is the 
 brighter. 
 
 The two gray bars are exactly alike in brightness; 
 but, by contrast with their backgrounds, one becomes a 
 light gray and the other a dark gray. 
 
 There are two kinds of contrast, successive and sim- 
 ultaneous. Successive contrast is in many respects 
 synonymous with after-images, and may be defined as 
 ''the apparent alteration of a gray or a colored surface 
 by the previous stimulation of the same retinal area 
 by some other sort of light." (Sanford.) Simul- 
 taneous contrast, the theme of the present chapter, is 
 described as ''the mutual effects in respect to color and 
 brightness which simultaneously seen but separated 
 visual areas have upon each other." (Baldwin.) The 
 difference between the two kinds of contrast lies in the 
 fact that one is due to successive impressions, whereas 
 the other is due to simultaneous impressions. The 
 effects of the two kinds of contrast are closely related. 
 
 Consider for a moment the practical consequences 
 of the phenomenon just demonstrated. Wherever sur- 
 faces of different brightness are seen together, each 
 modifies the brightness of the other. To see the world 
 of lights and shades as it really is, to guide ourselves 
 accurately in seeing form, relief, and distance, and to 
 be able to make the proper correction wherever contrast 
 operates, we must carry in our minds an idea of the 
 magnitude and a knowledge of the laws of brightness- 
 contrast. Contrast is both helpful and deceptive ; it 
 magnifies differences and therefore often helps in dis- 
 tinguishing surfaces; on the other hand, unless we 
 
VISUAL CONTRAST . 15 
 
 are prepared to make the correction, we are constantly 
 deceived as to the strength of lights and shades.* 
 
 2. Color-contrast. — Lay any two color-squares upon 
 the background; lay one of the gray bars upon each of 
 the colors and cover with the tissue-paper. Observe 
 that the gray of each bar assumes a distinct color-tinge. 
 Kecord the color of each bar. Kepeat the same with 
 other color-squares, pair by pair. If possible reduce 
 these records to a law of color-contrast. t 
 
 The two bars are colorless — exactly the same gray, 
 yet each shows a distinct tinge of color. Those who fail 
 to see one or more of the contrast-colors of these figures 
 
 * Supplementary Experiment. — (Not to be performed unless 
 directed by the instructor.) The following measurement of 
 brightness-contrast is very simple and effective and may be dem- 
 onstrated if a color-wheel or a color-top is available. Revolve 
 a black and a white disk upon the color-wheel and adjust the 
 proportions of black and white until the resulting gray matches 
 the gray bar on one square. Record the amount of white in the 
 mixture. Then measure the grayness of the other square in 
 the same manner. The difference in the amount of white in the 
 two measurements is a measure of the difference between the 
 two gray bars. 
 
 By similar procedure it is easy to determine how much of this 
 contrast-effect is due to the white and the black fields re- 
 spectively. 
 
 f A very pretty demonstration of color-contrast may be made 
 as follows: Put a large white paper or cloth upon a table; place 
 upon it some tall, slender object which will cast a long, narrow 
 shadow; pull down all window-shades except one which is left 
 open about a foot; light a candle or any other artificial light 
 and hold it a little to the side of the window. There will be 
 two shadows of the object, one from the white daylight and the 
 other from the yellow artificial light. The latter shadow is seen 
 distinctly blue. In reality, or physically, it is gray; the blue 
 is the contrast from the surroundings which are made yellow 
 by the artificial light. The induced blue is a much stronger color 
 than the inducing yellow. 
 
16 VISUAL CONTRAST 
 
 after a fair trial have a corresponding color-blindness or 
 color-weakness, which can be measured. 
 
 Color-contrast is most effective when there is no 
 brightness-contrast between the two fields. The effect 
 would have been very much enhanced in the present 
 figures if each gray bar had been matched in brightness 
 with the color-field upon which it rested. An otherwise 
 strong color-contrast may be almost obliterated by the 
 introduction of a simultaneous brightness-contrast.* 
 
 Here again we have a sweeping principle: all colors 
 tinge their surroundings with their complementary 
 color. Things are not what they seem ! The colors in 
 nature, art, fabrics — everywhere — are active and mod- 
 ify their environments. Flowers and foliage, grass and 
 sky, all play their harmonies and discords in modula- 
 tions of color. The artist trusts the subjective colors as 
 surely as he trusts the pigment on his canvas. The mil- 
 liner and the modiste use contrast effectively and 
 artistically: a dark hat and a green gown give a fair 
 and rosy complexion. There is almost as much in the 
 art of knowing what to avoid as in knowing what to 
 employ, t 
 
 3. Brightness-effect on Color. — Lay the black and 
 the white squares upon the background ; lay one of the 
 
 *-The color-contrast may be measured on the same principle 
 as the brightness-contrast. 
 
 •]• Chevreiil, "The Laws of Contrast of Color and their Appli- 
 cation to the Arts of Painting, Decoration of Buildings, Mosaic 
 Work, Tapestry and Carpet-weaving, Calico-printing, Dress, 
 Paper-staining, Printing, Military Clothing, Illumination, Land- 
 scape-gardening, etc.," is an interesting book, though somewhat 
 out of date. 
 
VISUAL CONTRAST 17 
 
 green bars upon each of these and cover with tissue- 
 paper. Record the effect of the black and the white 
 upon the green. 
 
 The colorless brightness of the surroundings modifies 
 the color near it. When placed upon similar fields, the 
 two greens are exactly alike ; but when placed upon 
 fields which differ in brightness, the greens appear to 
 change in brightness according to the laws of brightness- 
 contrast. A dark field makes an adjacent color brighter, 
 a light field makes it darker. 
 
 4. Color-effect on Color, a. Canceling. — Lay the 
 green and the gray squares upon the white background ; 
 lay a pale green bar upon each one and cover with the 
 tissue-]3aper. Record the effect of the deep green upon 
 the pale green. 
 
 h. Enhancing. — Lay one green bar upon the red 
 square and the other upon the gray and cover Avith the 
 tissue-iDaper. Record the effect of the red upon the 
 green. 
 
 c. Modulating. — Lay the yellow and the blue squares 
 upon the background ; lay a green bar upon each one and 
 cover w^ith the tissue-paper. Record the apparent 
 change in the color-tone of the two bars. 
 
 These three variations represent the three types of 
 effect of one color upon another. The two pale-green 
 bars are alike, but the one upon the green tends to lose 
 its color, while the one on the red is enhanced in color. 
 The green square throws a contrast red upon its bar and 
 this tends to cancel the green and produce a gray. This 
 illustrates how one color tends to obliterate a neighbor- 
 
18 VISUAL CONTRAST 
 
 ing color. Wherever shades or tints run together with 
 a more saturated form of the same color, the weaker 
 color must be made stronger to compensate for the loss 
 by contrast with its own but stronger color. 
 
 The field of the red square induces a contrast green 
 which reinforces the original green of the bar. The 
 effect of the red upon the green illustrates the general 
 law that opposites enhance each other, which is true for 
 both brightness and color. 
 
 The green on the yellow field looks bluish green 
 and the one on the blue field looks yellowish green. 
 These are illustrations of the law that colors which 
 are not complementary or identical have a modulat- 
 ing effect upon each other. This is by far the most 
 frequent of the three types of the effect of color upon 
 color. 
 
 This condition, that every color changes adjoining 
 colors, reduces itself, then, to a simple order and an 
 easily applicable law. The effect can always be pre- 
 dicted. Knowing the series of complementaries and the 
 principles of color-mixing, we can always predict the 
 result. 
 
 All these contrast-phenomena are very much stronger 
 in ordinary experience than under these experimental 
 conditions, because, in the experiment, we are not only 
 in a more critical attitude, but we are also biased by 
 the knowledge of the actual conditions, e.g., that 
 the gray bars are alike and that the green bars 
 are alike. In nature and in art, especially where we 
 are not conscious of the contrast, the illusion has full 
 play. 
 
VISUAL CONTRAST 19 
 
 5. Effect Immediate, a. Direct Observation. — Ke- 
 peat Exps. 1 and 2 and observe that the contrast is pres- 
 ent as soon as the object is clearly seen. 
 
 h. Comparison with After-images. — Determine the 
 shortest exposure-time which will bring out a noticeable 
 after-image of the black square. Kecord the approx- 
 imate time. 
 
 This experiment proves two things: first, that the 
 purely simultaneous contrast-effect is immediate and 
 is not due to adaptation; and, second, that it is very 
 closely related to the adaptation of successive contrast 
 or after-images in effect, so that the greatest care must 
 be taken to avoid complication of the two kinds of con- 
 trast as far as possible. After some training in obser- 
 vation one may obtain an after-image from a mere 
 glance at the figure. We seldom see an object so quickly 
 that adaptation does not play a role in the perception. 
 
 6. Effect Marginal and Reciprocal. — Lay the green, 
 the yellowish-green, the greenish-yellow, and the yellow 
 color-squares side by side in the order named, with edges 
 slightly overlapping. Observe them both with and 
 without the tissue-paper cover. Describe the changes in 
 these colors which are due to the juxtaposition. 
 
 Contrast, whether of brightness or color, is always 
 reciprocal. Which of the two or more fields shall show 
 the greatest effect depends upon the means of compari- 
 son, the relative area, the relative brightness, the 
 relative saturation, the j)oint of regard, and many other 
 conditions. When seen by itself, each of these squares 
 is of uniform color and brightness; but when seen to- 
 
20 VISUAL CONTRAST 
 
 getlier, the green brings out the yellow of the adjoining 
 less green square by counterbalancing the green of the 
 contrast red. The yellow brings out the green of the 
 less yellow square by counterbalancing the yellow with 
 the contrast blue. Each color makes the different ele- 
 ment in the contiguous color more conspicuous. Tlie 
 effect is striking even without the elimination of con- 
 tour by the tissue-paper. When the effect tapers off 
 rapidly from the margin, as in this case, it is spoken 
 of as marginal contrast. 
 
 Marginal contrast is one aspect of the general prin- 
 ciple that the contrast-effect decreases with increase in 
 the distance between the two contrasting surfaces. 
 Certain conditions tend to make it prominent, as here, 
 but there has been opportunity for observing the fact 
 in every experiment. 
 
 7. Area. — Place a gray bar and the gray square some 
 distance apart upon the background and cover with the 
 tissue-paper. Record which appears to be the darker. 
 
 The two gi'ays are really alike, but the bar looks the 
 darker on account of its relatively small area and the 
 form which is favorable to the exposure from the white 
 inducing field. In all the above experiments the effects 
 have been reciprocal, but we have directed our attention 
 to the smaller areas because they show the greatest 
 relative effect. 
 
 8. Contour. — Compare the force of the contrast in 
 Exps. 1 and 2 when the squares are covered with the tis- 
 sue-paper witli the force when they are not covered. 
 Record the difference in the effect. 
 
VISUAL CONTRAST 21 
 
 The observer has imdoubtedly been annoyed and 
 puzzled by the constant demand for covering with 
 tissue-paper. What can be its jDurpose ? The tissue- 
 paper has been employed for the purpose of eliminating 
 contour, and that only. This has been done on the 
 principle that contrast is very much enhanced by un- 
 certainty in the surface. Surfaces with very sharp 
 delineations counteract the motives for contrast. 
 
 There are other ways of eliminating contour. 'Nsl- 
 ture as a rule presents more or less uncertain contour 
 and therefore favors contrast. Distance, for example, 
 serves the same purpose as the tissue-paper. When we 
 admire a flower-bed or a landscape we are far enough 
 away to get the dim outline and the vagueness of con- 
 tour which are so favorable for contrast.* 
 
 9. Contrast in the After-image. — Lay one gray bar 
 upon the black square and the other near by upon the 
 white background ; cover with tissue-paper. Fixate a 
 point between them and secure an after-image. Record 
 the relative brightness of the two bars in the after- 
 image. 
 
 The contrast is effective in the after-image. 
 
 The explanation of visual contrast in color and 
 brightness is probably to be found chiefly in physiologi- 
 cal terms^ — in the indirect stimulation of adjacent areas 
 of the retina. 
 
 * The color-wheel serves the same purpose. If we cut three 
 concentric gray circles of different brightness and place them on 
 the wheel, the contrast will hardly be perceptible so long as the 
 wheel is motionless; but revolve the disk and the contrast at once 
 becomes conspicuous, because the spinning takes away the sharp 
 rigidity of outline and surface. 
 
22 VISUAL CONTRAST 
 
 The experiments have all been devoted to color and 
 brightness. The phenomena of visual contrast might 
 have been equally well illustrated in visual perception 
 of space. The general law is that opposites enhance 
 each other although the actual explanation for this may 
 be different in different cases. As black enhances white 
 and red enhances green, so there is a reciprocal enhance- 
 ment betAveen the long and the short, the large and the 
 small, the narrow and the wide, the irregular and the 
 regular, the dull and the sharp, the smooth and 
 the rough, the straight and the crooked, the ugly and 
 the beautiful, etc. When the tall and the short man 
 walk together, the tall one looks taller and the short 
 one looks shorter than otherwise. A poor penman is 
 mortified to see his signature together with the signa- 
 ture of a good penman. A pocket-knife is dull in com- 
 parison with a razor, but sharp in comparison with a 
 hatchet. 
 
 Similar illustrations might be found in the time, or 
 duration, of visual acts. Contrast operates in all the 
 attributes of sensation — quality, intensity, duration, 
 and space. And we find it in all the senses. Indeed, 
 one of the laws of contrast is that it is strongest in 
 those senses with which we make the poorest discrimina- 
 tion. Hence the most striking illustrations of contrast 
 are found in the lower senses, as in taste, smell, and 
 temperature. 
 
CHAPTER III 
 THE VISUAL FIELD 
 
 For One. 
 
 Tjie problem is to measure the field of vision for 
 white and colors, and to determine some characteristic 
 color-changes in the indirect field. 
 
 Make the following preparation for the experiment: 
 Lay a piece of cardboard back of Fig. 1. Prick through 
 the page with a pin at each nmnber on the arc, at the 
 free end of the heavy line, and at the principal points in 
 the light line. Trim the card by cutting according to 
 the tracing of the light line. Insert the degree-numbers 
 at the appropriate points. Draw the heavy line. 
 Punch a pinhole at the free end of the heavy line, 
 which is the center of the arc. Put a thread through 
 the hole and tie a knot at the back of the card. Tie a 
 knot at the other end of the thread, fifty centimeters 
 away. Take the large black square and the small white, 
 red, green, yellow, and blue squares from the book envel- 
 ope. Lay the white square upon the large black square 
 as a background; then stick a pin through the knot at 
 the free end of the cord, through the two squares near 
 a corner of the small one, and finally through a cork 
 
 23 
 
24 
 
 THE VISUAL FIELD 
 
 which may serve as a handle. The quadrant and ob- 
 ject-card thus arranged may be called a perimeter.* 
 
 Fig. 1. 
 
 The perimeter is a simple means of measuring the 
 direction of an object in the indirect field of vision. 
 
 * There have been two general types of instruments employed 
 in perimetry of vision : { 1 ) those in which the measurements 
 are made upon a plane surface, and (2) those in which the 
 measurements are made upon the arc of a circle centered at 
 the eye. The former is called a campimeter, the latter a per- 
 imeter. The present outfit works on the perimeter principle. 
 The most effective perimeter is an instrument with colored lights 
 in a daric room. 
 
THE VISUAL FIELD 25 
 
 Seat yourself in good reflected light with the back 
 toward the source of light. Mark a dot on a piece of 
 white paper and fasten it up sixty centimeters directly 
 in front of the eyes. Blindfold one eye ; hold the 
 quadrant with one edge close to the other eye so that 
 in looking straight forward at the dot, the eye sights 
 along the heavy straight line on the quadrant. When 
 the eye is fixed upon it, the dot becomes the fixation- 
 point, or point of regard, and is said to lie in the direct 
 field of vision. The visual space around it is spoken of 
 as the indirect field. 
 
 1. The Field for White.— Hold the quadrant in 
 the horizontal plane in front of the right eye so that 
 the regard-line on the quadrant points exactly toward 
 the fixation-point when you sight along it. Keep the 
 head upright and firm. Fixate the dot which is the 
 point of regard and do not allow the eye to wander away 
 from it during the actual trial. Move the object-card 
 inward from the extreme right until the white disk can 
 first be seen as white.* The thread being held taut 
 will indicate the number of degrees from the line of 
 regard. Record this. Make five trials, and find the 
 average and the mean variation for these.f 
 
 Proceed in the same manner and measure along the 
 other three cardinal radii, namely, with the white enter- 
 ing from below, from the left, and from above. 
 
 * Move inward at such a rate that the destination is reached 
 in about eight seconds. Take special care that the head does 
 not turn or the eye wander from the point of regard, and that 
 the point of regard is directly in front of the eye. 
 
 f The mean variation (m. v. ) is a measure of the degree of 
 agreement in a series of records. It represents the average of 
 
26 THE VISUAL FIELD 
 
 To represent these results graphically, draw four 
 radii from a point representing the point of regard — 
 one to the right, one to the left, one down, and one 
 up, — and place a dot on each radius to represent the 
 corresponding measurement on the scale of one milli- 
 meter to one degree. Mark each of these dots w."^ 
 
 These results are stated with reference to the field 
 of vision ; they might equally well have been stated in 
 terms of regions on the retina. The outer or temporal 
 field of vision corresponds to the inner or nasal region 
 of the retina, and the upper field of vision corresponds 
 to the lower region of the retina. The temporal field 
 of vision is larger than the nasal, and the lower is 
 larger than the upper. This difference is due to the 
 limitations placed by the nose, cheek-bone, and 
 brow.t 
 
 the deviations of each individual record from the average of all 
 the records for the group, regardless of sign. Thus 
 
 75 - 
 
 1 
 
 73 - 
 
 3 
 
 78 - 
 
 2 
 
 80 - 
 
 4 
 
 75 - 
 
 1 
 
 5)381 5)11 
 
 Ave. 76 2.2 m. V. 
 
 *Thus, if the white square was first seen as white at fifty de- 
 grees above the eye, put a dot fifty millimeters from the center 
 on the appropriate radius. 
 
 f Supplementary Exercise. — There is a totally blind spot in the 
 nasal region of each eye. It is located at the point of entrance 
 of the optic nerve, about fifteen degrees from the fovea, or point 
 of clearest vision. If this exercise is assigned, the student should 
 devise his own methods and means for one or more of three 
 exercises: (1) to locate the blind spot; (2) to survey and de- 
 termine its shape and area; and (3) to determine how it is filled 
 out in perception. 
 
THE VISUAL FIELD 27 
 
 2. The Fields for Colors. — Substitute the red square 
 for the white and determine the limits ^ for red on the 
 two meridians, right and down, making five trials for 
 each.t Compute the average and mean variation and 
 insert the averages on the two corresponding radii of the 
 chart for Exp. 1 and mark them r. 
 
 Measure and record in the same manner for yellow, 
 blue, and green. 
 
 Assuming that the results for the meridians selected 
 are typical of what we should find in the other me- 
 ridians in regard to the order of limits, this and the 
 foregoing experiments demonstrate that the color-fields 
 are all smaller than the field for white; and, in the 
 normal eye, the colors supplied have fields which vary 
 in magnitude in the order yellow, blue, red, and green. 
 There is such a large difference that the field for green 
 has less than one-fourth the area of the field for yellow. 
 
 How does this affect our ordinary perception of 
 color in the indirect field of vision? If we look 
 steadily at one flower in a flower-bed and attempt, 
 without movement of the eyes, to see the coloration of 
 the whole bed, we observe that, outside of a certain 
 narrow limit, the leaves do not look green; beyond a 
 somewhat larger limit, no flowers are seen red, al- 
 though the blue and yellow ones look brilliant; and in 
 the outermost parts of the bed all flowers and leaves 
 
 * The observer knows what the color is to be, and the task 
 is to discover the limit at which he can identify the disk as be- 
 ing of that particular color. The inward movement should begin 
 just clearly outside the field and be made at such a rate that 
 the limit is reached in from five to ten seconds. 
 
 f If desired, these color squares may be cut smaller, but the size 
 must be recorded. 
 
28 THE VISUAL FIELD 
 
 look gray. This is literally true, but not alarming, 
 because we do not usually look at flower-beds in that 
 way. When we Avant to see the color of a bed of flow- 
 ers, a painting, or a sky, we regard (that is, pay at- 
 tention to), or apperceive, only the color of the direct 
 field at and around the point of regard ; our eyes sweep 
 back and forth over the object automatically with as- 
 tonishing swiftness and take a series of snaj^shots, as 
 it were, on the central portion of the retina, and then 
 we combine these into a whole in memory, although the 
 process is almost instantaneous and seems to be a single 
 act of perception. We have the feeling that the color- 
 impressions from the direct and indirect fields are 
 simultaneous, but the fact is that we have memory- 
 images of impressions from different parts of the object 
 and the simultaneous impressions from the whole object 
 become merely a sort of plat on which we unconsciously 
 distribute these impressions and reconstruct the true 
 color-relations. 
 
 If we had used the four truly fundamental colors,* 
 the absolutely complementary pairs, yellow and blue, 
 and red and bluish green, and had reduced them to the 
 same brightness and saturation, we should have found 
 that the limits for blue and yellow coincide and those 
 for red and gTeen coincide. In Fig. 2 the inner curve 
 represents the red-green boundary and the outer the 
 yellow-blue boundary. The shading shows the limit for 
 
 * The colors which answer for this purpose are very difficult to 
 obtain. Tliose furnished are neither fully complementary nor of 
 the right hue as fundamental colors. They also differ much iu 
 brightness. 
 
THE VISUAL FIELD 
 
 29 
 
 white and slioiild be compared with the record in 
 Exp. 1. 
 
 Thns, the retina may be conceived of as being divided 
 into three zones: (1) a central zone over which all 
 colors and brightnesses can be seen; (2) a middle zone 
 over which only bines and yellows and their derivatives 
 can be seen; and (3) an outermost zone over which all 
 objects, colored and nncolored, appear gray. Let ns 
 
 Fig. 2. 
 note some of the most significant applications of this law 
 of distribution. 
 
 Color-vision is made possible by the existence in the 
 retina of the so-called color-elements. There are many 
 theories in regard to the probable number of these. 
 The close coincidence of these two pairs of colors tends 
 to support the conjecture that the retina contains either 
 
30 THE VISUAL FIELD 
 
 two doubly-functioning or two pairs of color-elements, 
 one for red-green and one for yellow-blue. The psycho- 
 logical chart of the fields of color-vision must therefore 
 be used as one of the criteria of a physiological theory 
 of the nature and distribution of the color-elements. 
 
 The three zones probably indicate as many epochs in 
 the evolution of color-vision. The primitive eye was 
 sensitive only to brightness ; some of these elements in 
 the central portion of the retina differentiated and be- 
 came sensitive to yellow and blue, and these elements 
 spread gradually, during evolutionary ages, from the 
 fovea to the periphery of the retina and have now 
 reached the expanse outlined by the yellow-blue curve 
 in the chart ; very much later, a higher differentiation 
 of the elements at the fovea resulted in the development 
 of sensitiveness to red and green and these elements 
 are now spreading toward the periphery but have not 
 yet reached farther than the limits which correspond 
 to the red-green curve in Fig. 2.* 
 
 This arrangement also becomes an explanation for 
 the well-known fact about color-blindness, that by far 
 the most numerous cases of color-blindness are of the 
 red-green type. Why should this be so ? There is a 
 well-kno^\Ti biological law to the effect that, in general, 
 the last acquired structure is the first to become defec- 
 tive or to be lost. ^N'ow, the red-green elements are the 
 least stable because they have been acquired most 
 recently, and therefore a person is much more likely 
 
 * All colors other than the fundamental are mixtures of two 
 or more of the fundamental colors. Hence the four color-elements 
 can produce all the experienced color-effects. 
 
THE VISUAL FIELD 31 
 
 to be red-green blind than yellow-blue blind, if his color- 
 vision is defective. 
 
 These zones, as determined in the experiments upon 
 which Fig. 2 is based, are not fixed except for the par- 
 ticular conditions specified. Among the conditions 
 which determine the limits of the zones the following 
 may be noted : 
 
 a. Color tone. — The four colors in this experiment 
 go by the same name as the four upon which Fig. 2 
 is based, but the two sets of colors differ very much in 
 tone and the results vary accordingly. 
 
 h. Saturation or Purity. — As a rule, the purer the 
 color the larger the field. 
 
 c. Btnghtness. — The brighter the color or the gray 
 the larger will be its field. One of the chief causes for 
 the difference between the record in this experiment and 
 in the curves in Fig. 2 is that of brightness ; in a stand- 
 ard experiment the colors are all reduced to the same 
 brightness, while in the common tones as here used 
 there is a great difference in brightness. As the illu- 
 mination of the colored stimulus is increased the field 
 is enlarged. 
 
 d. Area or Magnitude. — Within certain limits, the 
 larger the colored object the larger is its field. 
 
 e. Background. — The background has profound in- 
 fluence upon the color. Numerous laws of the rela- 
 tion of the peripheral color to its background have been 
 worked out. In general for mixed colors (all pigment 
 colors) the field is largest when the contrast between 
 the background and the color is the greatest. 
 
 /. Adaptation and Fatigue. — It makes a difference 
 
32 THE VISUAL FIELD 
 
 whether the eye has become adapted to darkness or to 
 some kind of light before a trial. The rested eye is 
 more efficient and gives a larger field than the non- 
 rested eye. Retinal fatigue shows itself more rapidly 
 in a retinal area the farther the area is away from the 
 fovea. We have only to recall what we learned in the 
 two foregoing chapters to realize what a large variable 
 this is. It is necessary to make comparatively rapid 
 movements in order to secure the best results. 
 
 g. Practice. — It is probable that the extension of the 
 color-fields as the result of practice is not an increase 
 of sensitivity in the retinal elements, but merely a de- 
 velopment in capacity for observation. 
 
 li. Age. — Color-fields enlarge with age. The differ- 
 ence between the field of a boy of ten years and one 
 of twenty is large; but we do not know how much of 
 this is due merely to the former's lack of power in appli- 
 cation and skill in observation. 
 
 i. Disease. — Certain nervous diseases are character- 
 ized by peculiar changes in the fields of color. There 
 may be, for example, general contraction of the color- 
 fields, loss of vision in one half of the retina, impair- 
 ment in the vision of certain colors, or central color- 
 blindness. This last-named defect often results from 
 nicotine-poisoning; it is discovered by the fact that, in 
 order to see colors, the patient must view the object by 
 indirect vision. 
 
 j. Color-hlindness. — This is a large topic by itself. 
 About one per cent of all women and more than four 
 per cent of all men are distinctly blind to some colors ; 
 and indeed the most recent and most efficient tests of 
 
THE VISUAL FIELD 33 
 
 color-blindness make it seem probable that these figures 
 are underestimations. 'No one can have come success- 
 fully to the present stage in this course without dis- 
 covering whether or not his color-vision is defective. 
 
 Jc. Arbitrary Limits. — A color comes into its field 
 gradually ; the magnitude of the field therefore depends 
 upon what degree of resemblance to the color as seen 
 in direct vision the observer has set himself as a 
 standard for the purpose of the measurement. The 
 incoming color is never exactly like the color as known 
 through direct vision. 
 
 3. Transition Colors. — Starting to the right, outside 
 the color-field, and going by ten-degree steps toward the 
 point of regard, observe and record the color of the red 
 square as it appears at the first momentary impression 
 in each step. Make three independent series of trials."^ 
 
 Eecord three series of observations for yellow in the 
 same manner. t 
 
 According to the Hering theory of color-vision, there 
 are four '^Urfarben", that is, primary or fundamental 
 colors. All other colors may be built up from these, 
 and to them the color elements in the retina correspond. 
 They are the two pairs of perfect complementaries 
 spoken of in Exp. 2. They undergo no change when 
 passed outward through the indirect field and are there- 
 fore called stable colors. All other than the stable 
 
 * If the right eye shows fatigue, this and the following ex- 
 periments may be made with the left eye. The practice gained, 
 however, makes it easier to use the right eye. 
 
 ■j- The record must necessarily be a crude description of the 
 changes in color and brightness. 
 
84 THE VISUAL FIELD 
 
 colors undergo more or less radical changes when passed 
 through the indirect field, as in this experiment. The 
 following is a typical record, though much abbreviated:* 
 
 ^, • Transition colot'S : the same color wJien 
 
 i,oior as seen m passed inivard thrcnigh the indirect 
 
 lite direct jieia. fi^i^ appeared successively as follows. • 
 
 Deep red Yellowish, yellow, orangisli yellow, yellow- 
 orange, orange-red, red. 
 
 Reddish orange Yellowish, orangish yellow, reddish orange. 
 
 Orange-yellow Yellowish, yellow, orangish yellow. 
 
 Green Yellowish, yellow, greenish yellow, green. 
 
 Blue Blue. (This happened to be the stable blue.) 
 
 Violet Bluish, blue, violet. 
 
 Purple (red end) ...Yellowish, orange-yelloAV, yellow-orange, 
 orange-red, red, purplish red, reddish pur- 
 ple, purple. 
 
 This record expresses a general law: the colors of 
 the red end of the spectrum first appear as yellowish or 
 yellow in the outer regions of the field of vision, while 
 those of the blue end first appear as bluish or blue. 
 Red, orange, yellow, and green come in with a yellow- 
 ish tinge, while blue and violet come in with a bluish or 
 blue tinge. 
 
 Every color enters the field of vision as a gray. 
 Within the yellow-blue zone all colors appear in some 
 aspect of yellow or blue, if they are seen as colors. 
 Only within the central zone can the reds and greens 
 and their derivatives reveal their true color. A com- 
 parison of this statement with the above law makes 
 what is otherwise an apparently chaotic condition of 
 affairs seem natural and intelligible. 
 
 'to-" 
 
 *From Baird's "The Color-sensitivity of the Peripheral Retina," 
 Publication 29, Carnegie Institution. The present chapter is based 
 mainly upon this monograph. 
 
 i 
 
THE VISUAL FIELD 35 
 
 The pigment colors of papers and fabrics are always 
 mixed colors. The reds, oranges, and greens, for ex- 
 ample, contain considerable yellow, and it is this yellow 
 which becomes dominant and represents those colors 
 within the yellow-blue zone. In the same way, it is the 
 blue of the violet end which represents violet outside 
 of the red zone. 
 
 All colors also undergo characteristic changes in 
 brightness in passing through the indirect field. 
 
 4. Adaptation Colors. — Hold the red square at 25° 
 on the right meridian for about ten seconds, being care- 
 ful to maintain a steady fixation on the point of regard, 
 and observe the changes the color goes through in that 
 time. Record from memory. Make three trials, allow- 
 ing adequate rest. 
 
 Repeat the same for yellow. 
 
 Constant stimulation of a given area of the peripheral 
 retina produces definite cycles of change in brightness 
 and color. The following is a typical record of the 
 changes for three seconds by a trained observer : 
 
 , Adaptation colors : the mccession 
 
 Color as ^^^^ij^ of colors this object revealed in a 
 
 the direct jield. three-second exposure at 30° right. 
 
 Red Red, orange, yellow, white, blue. 
 
 Orange Rich orange, yellowish orange, yellow. 
 
 Yellow Orange-yellow, yellow, gray, bluish. 
 
 Green Yellow-green, yellow, gray, bluish. (25°.) 
 
 Blue Blue, gray, yellowish. 
 
 Violet Blue ?, blue, bluish. 
 
 Purple Red, orange-red, orangish. (25°.) 
 
 From records of this kind we derive a law which 
 expresses a cycle of three stages: the colors of the red 
 
36 THE VISUAL FIELD 
 
 end of the spectrum pass toward yellow, and those of 
 the violet end toward blue; then follows a momentary 
 gray ; and then appears the complementary color of the 
 one jnst before the gray. 
 
 In the above fragment of a record, these three stages 
 are represented in the case of red, yellow, green, and 
 blue; the other colors did not complete their cycles 
 within the time limit. 
 
 The reasons for this law of adaptation are as fol- 
 lows : * The peripheral retina is not much used and 
 
 * Dr. Baird describes this process in a personal letter as fol- 
 lows: "The reasons for the existence of these characteristic 
 phenomena of adaptation or exhaustion are these : The peripheral 
 regions of the retina contain but a relatively scant supply of 
 color-sensing substance; and they, too, are very seldom employed 
 in the vision of every-day life. Consequently the advent of 
 retinal exhaustion must be relatively rapid when these regions 
 are stimulated. Now, the pigment colors which w^e ordinarily 
 see are not pure, but mixed colors; green leaves and red ribbons 
 contain a considerable admixture of yellow, orange, blue, etc. 
 Hence, when a colored object stimulates the peripheral retina, 
 its stimulation is not confined to a single color-sensing substance, 
 as would be the case if certain pure colors were employed. The 
 impure red of the ribbon may affect both the red-sensing sub- 
 stance and the yellow-sensing substance of the retina. Reasons 
 for believing that the yellow-sensing substance is more stable and 
 persistent in function than the red-sensing substance have al- 
 ready been cited. So long as both these substances continue 
 to function in approximately equal degree, a red (or yellowish 
 red) ribbon will be seen. But in proportion as the red-sensing 
 substance becomes exhausted — by reason of its scantiness or as 
 a result of its lesser tenacity of function — the function of the 
 yellow-sensing substance becomes dominant in the visual process; 
 the ribbon which originally seemed red now appears yellowish or 
 even yellow. This marks the completion of the first phase of 
 the color process of indirect vision, and the beginning of the 
 second phase. If the ribbon still continues to stimulate the 
 same retinal region, the yellow-sensing substance will in turn 
 become exhausted; and tlie ribbon will appear gray so long as 
 the black- white substance continues to function alone. When 
 this third stage of adaptation is reached the retinal region is 
 completely exhausted. But this peculiar condition of adapta- 
 
THE VISUAL FIELD si 
 
 therefore fatigues with embarrassing rapidity. The 
 colors we ordinarily see are all mixed, and the yellow 
 or blue element in a mixture is more stable than the 
 red or green, for reasons explained under Exp. 2 ; hence 
 the latter fatigues more quickly and falls out, leaving 
 the other dominant. This is the goal of the first stage. 
 Then follows the process of adaptation, as in after- 
 images, when the stable color element becomes fatigued, 
 and leaves a blank or gray. Then follows the last stage, 
 which corresponds to the after-image of the strongest 
 element in the first stage. "^ 
 
 The fact of order in these changes is perhaps as 
 astonishing as their rapidity. Our common experience 
 of these changes in daily life has resulted simply in a 
 distrust — both conscious and unconscious — of indirect 
 color-vision. When we think of it, we think of it as 
 chaotic; when we inadvertently follow it, we feel 
 uneasy; in normal perception we automatically neg- 
 lect it. 
 
 These four experiments may suffice to give a glimpse 
 of the complexity and wonderful arrangement of the 
 color-fields and to point the way in which the scientific 
 attitude is rewarded by revelation of system and reason 
 
 Hon does not last long. A process of regeneration takes place 
 within the organ; and so long as the retinal regeneration contin- 
 ues, one sees color whether the colored object be present or not. 
 This fonrth stage of the visual process is analogous to that 
 which you studied in your experiments with after-images. The 
 visual sensation Avhich now appears in indirect vision is com- 
 plementary to the color which was present in the second stage." 
 * It is remarkable that after-images are never observed in the 
 periphery of the dark-adapted retina, and very rarely more than 
 30° from the fovea. They may be observed, however, in the per- 
 iphery of the light-adapted retina. 
 
38 THE VISUAL FIELD 
 
 in it all. Many of the i)roblems of indirect color-vision 
 have not even been mentioned, and conditions and vari- 
 ables have been stated in the barest way possible. •' 
 
 In conclusion, let us notice a beautiful biological 
 arrangement. If we compare the direct with the in- 
 direct field with reference to sensitiveness, we find that 
 we are most sensitive to color and form in the direct 
 field, and to light and movement in the indirect field. 
 That is, we can see color and form most accurately when 
 the image falls upon the central region of the retina, 
 but we can detect movements and changes in brightness 
 more readily when the outer-lying portions of the retina 
 are stimulated.- 
 
 This is a story of adjustment and it suggests to us 
 the real office of the indirect field. The central region 
 of the retina, corresponding as it does to the direct 
 field, is the organ of attention, of concentrated mental 
 activity, which represents the environment in terms of 
 space and color; while the indirect field is merely ac- 
 cessory. Its functions are those of a scout or guardian. 
 The life-preserving value of this arrangement is clear. 
 Consciousness is warned of the presence or approach of 
 an object beneficent or noxious to life, by impressions 
 of luminosity or movement in the indirect field. If 
 then the signal is heeded, the eye quickly turns so as 
 to bring the object of scrutiny into the direct field where 
 its true nature can be seen accurately, by the most 
 efiicient and economical expenditure of energy. 
 
CHAPTER IV 
 VISUAL SPACE 
 
 For One* 
 
 Although we have several space-senses, most of us 
 live predominatingly in a world of visual space. 
 Visual space-perception is therefore one of the largest 
 and most important topics in psychology. We shall 
 limit our experiments in this chapter to a few features 
 of visual space images. 
 
 1. Outv^ard Projection of the Visual Image. 
 
 a. Floating Flakes. — Look toward the sky with your 
 eyelids almost closed and observe a sort of snowfall 
 effect. Describe it. 
 
 These flakes are the shadows, on the retina, of 
 particles floating in the vitreous humor. They are pro- 
 jected as objects in outer space in accordance with the 
 law of outward projection.f 
 
 * This chapter presupposes knowledge of the structure and 
 function of the eye, as outlined in the text-books on psychology. 
 
 f " We see indistinct motes floating about in the field of view 
 and slowly gravitating downward. Sometimes they are undu- 
 lating, transparent tubes, with nucleated cells within; some- 
 times they are like inextricably tangled threads, or like matted 
 masses of spider's web; sometimes they are slightly darker spots, 
 like faint clouds." (Le Conte.) 
 
 39 
 
40 VISUAL SPACE 
 
 h. Shadoivs of the Retinal Blood-vessels." — Stand- 
 ing in a dark room with one eye closed, wave a candle- 
 flame or burning match gently in a small circle close 
 to the side and slightly downward and forward from the 
 other eye; look at the opposite wall and you will see 
 a network like Fig. 3.t 
 
 Describe size, distance, color if any, stability, etc. 
 
 Fig. 3. 
 
 The retinal blood-vessels enter at the same point as 
 the ojitic nerve and spread in a network inside of 
 the retina. As the rods and cones lie back of this layer, 
 the blood-vessels cast shadows which become visible 
 under the prescribed conditions of illumination. There 
 is nothing on the wall to correspond to this system, yet 
 you see it distinctly out there in space, in accordance 
 with the law of outward projection. 
 
 We are never directly aware of the retinal impression. 
 
 * Perform this experiment in the evening, if necesScary. 
 
 f Do not fatigue tlie eye. Nothing is gained by straining it. If 
 you do not get the effect at once, it is because it seems unreason- 
 able to look for such a thing. Look for a network like Fig. 3, 
 very much enlarged, and you will see it. The experiment should 
 not require more than a minute or two. 
 
 1 
 
VISUAL SPACE 41 
 
 We always see objects out in space. The retinal im- 
 pression is automatically referred to its normal source : 
 that is the law of outward projection. The history of 
 the evolution and development of this tendency consti- 
 tutes one of the most important chapters in psychology 
 as well as in the theory of knowledge. 
 
 The conditions of the above experiments were un- 
 usual, if not unnatural, but the mind responded in its 
 habitual way, and this misdirected tendency revealed 
 to us something of the nature of the normal process. 
 The image was laid bare, as it were, by the absence of 
 the object. 
 
 The retinal light furnishes us another illustration of 
 this class of entoptic phenomena.* But the best and 
 most serviceable illustration of all is the after-image, 
 with which we are already familiar. It represents a 
 physiological condition of the retina but is always seen 
 out in space, never within the eye.f 
 
 * To observe the retinal light, go into a dark room and cover 
 your eyes so as to shut out all possibility of objective light. 
 Behold, in a moment you see a gorgeous array of colors in front 
 of the eye. They tend to grow brighter, usually fashion them- 
 selves into fantastic designs, and are in a continual kaleidoscopic 
 commotion. These are nothing but the projection of the local 
 irritation of the retina, chiefly through the circulation of the 
 blood. These retinal lights are the stuft' from which many visual 
 dreams are "made". 
 
 f "'Seeing stars" from a blow or fall illustrates the same princi- 
 ple. The story is told of a man who was attacked and knocked 
 senseless by a blow on the temple during a pitch-dark night. He 
 accused a neighbor whom he had to confront in court with the 
 evidence, which was essentially this : "It was pitch-dark, but the 
 moment I felt the blow there was a great flash by the light of 
 which I saw my assailant." This may have been naive testimony: 
 he had seen a light at the proper time; he suspected his neigh- 
 bor; his conviction was that he had seen his neighbor. 
 
42 VISUAL SPACE 
 
 2. The Line of Projection, a. Projection of the 
 After-image. — Repeat Exp. 6, Cli. I. 
 
 The two spatial factors in the outward projection are 
 distance and direction. We are here concerned with 
 direction. The law of visible direction may be stated 
 thus : When the rays from any radiant strike the ret- 
 ina, the impression is referred back along the ray-line 
 into space. The retina is a small copy of the plane of 
 projection, a plane across the visual field at right angles 
 to the line of regard. This is illustrated in Fig. 4. 
 
 Fig. 4. 
 
 Every point in the plane of projection has a correspond- 
 ing point on the retina. When the retina is stimulated 
 at Cy let us say, the image is referred back along the ray- 
 line c-c and the object is seen in that direction. If an 
 area, e.g. 6-e, is stimulated, the object will be seen in the 
 corresponding area e'-h' in the plane of projection. 
 The experiment shows that the size of the after- 
 
VISUAL SPACE 43 
 
 image varies with the distance of the plane of projection. 
 This law of size of the retinal image may be derived 
 from the above law of direction. It is illustrated by the 
 four arrows in Fig. 4, which are all projections of the 
 same image but at different distances."^ 
 
 h. The Size of the Retinal Image. — To determine 
 the length of the retinal image of your pencil held up- 
 right at a distance of 50 centimeters in the line of re- 
 gard, proceed as follows: Let the arrow eb\ Fig. 4, 
 represent the pencil, eh its image upon the retina, and 
 n the nodal point in a simple scheme of the eye. The 
 two triangles e'h'n and ehn are similar. The distance 
 an in the normal eye is about 16 millimeters; the dis- 
 tance an is by direction 50 centimeters; you measure 
 the length of the pencil. You then get the proportion 
 e'n : e'h' : : en : eh, or x, the length of the retinal 
 image. Assume that the retinal image is on a flat 
 surface in order to simplify the equation. 
 
 c. The Inversion of the Retinal Image. — Make a pin- 
 hole in a card and hold it toward the light about 10 
 centimeters from the eye. Looking at the pinhole, hold 
 the head of a pin very close to the eye, and in front of 
 the pupil, and observe that you see the pin inverted 
 back of the card. 
 
 Pierce five pinholes close together and proceed as 
 before. Kecord how many pins you see. 
 
 *To illustrate how little attention we pay to the analysis ot 
 perceptions, a professor asked a large class in psychology to 
 estimate how large the image of the moon at the horizon would 
 appear if projected upon a plane at arm's length from the eye. 
 The estimates of the diameter were nearly all too large; as, the 
 size of a dollar, a saucer, or a wagon-wheel, but one man said. 
 "The size of a pea," and he was right. 
 
44 VISUAL SPACE 
 
 Examination of Fig. 4 showed that normally all rays 
 cross at the nodal point in the eye, and this results in 
 the reversal of the image: what is np in the plane of 
 projection becomes down on the retina; and what is 
 right becomes left. This is true, however, only when 
 the object is at such a distance that the rays from it can 
 pass proj^erly through the lens and form an image on the 
 retina. E'ow, in this experiment, the pin was held too 
 close to the eye to allow a clear retinal image, and it 
 was so close as to cast a good shadow upon the retina. 
 This shadow is not inverted on the retina, but it is pro- 
 jected according to the normal law of visible direction 
 for inverted images, and the result is that it is seen in- 
 verted in the plane of projection. 
 
 Our normal projection of the retinal image is a habit 
 based, indeed, upon neural mechanism and inherited 
 tendency, yet subject to modification by training. If 
 we should Avear, for a month, prism glasses which com- 
 pletely and consistently reversed the whole visual field, 
 we should in that time acquire new habits of projection 
 and be able to harmonize the reversed retinal images 
 with the touch and movement experiences. Space- 
 perception is always a complex process of associa- 
 tion and interpretation, though normally extremely 
 abridged. 
 
 d. The Muscular Sensations of Position of the 
 Eye. — Roll a sheet of paper into a tube one inch in 
 diameter. Hold your left hand about 12 centimeters 
 in front of your face ; place the tube in front of the right 
 eye, lean it against the hand and point it toward some 
 distant object. 'Now look wdth both eyes (in spite of 
 
VISUAL SPACE 45 
 
 the fact that the hand is in the way of the left eye) at 
 the distant object and you will see it and a circular sec- 
 tion of its surroundings through a round hole in the 
 palm of your hand. 
 
 So far, we have considered the retinal image as a 
 basis for the perception of direction. But muscular 
 impressions of position and movement of the eyeball 
 are of no less importance, formally the two cooperate. 
 Thus, in perceiving the direction of a flock of birds in 
 the distance, the head turns in the approximate direc- 
 tion, then the eyeballs turn for finer adjustment and 
 sweep back and forth from one object to the other, 
 measuring the angular difference in direction, and 
 finally the local sign * of the retinal image indicates the 
 relative direction of the different birds in the flock. 
 The perception of form is, of course, merely the percep- 
 tion of a complex system of directions, t 
 
 This experiment illustrates the rigidity of these 
 muscle-sense marks of direction. The hole in the hand 
 is clean-cut and absolute : it is a very striking illusion. 
 The local sign of the retina is so rigid and the position 
 of the eyeball is sensed so accurately that we see the 
 objects upon which the eyeballs were converged in the 
 true direction in spite of the intervening obstacle. 
 
 * Local sign is that special character of a sensation whereby we 
 are enabled to refer it to a particular place, "that diflFerential 
 quality of a sensation which varies with the part of the sensitive 
 surface stimulated, but not with the nature of the stimulus." 
 (Stout.) 
 
 f Normally we are not conscious of either location of the retinal 
 image or the sensations of muscular adjustment in the eye. The 
 process of vision has become so abbreviated and automatic that we 
 merely have a sort of direct awareness of direction without know- 
 ing why or how we become aware of it. 
 
46 VISUAL SPACE 
 
 3. Accommodation. — a. Range : the Near-point of 
 Vision. — Hold the point of a pin close in front of one 
 eye (the other eye covered) and observe that you can- 
 not see it clearly. Move it back and forth and find the 
 nearest point at which you can see it without a blur. 
 That point is called the near-point of vision. Kecord 
 the distance from the eye. 
 
 If we are to have a clear image of the point, the rays 
 of light reflected from that point must come to a focus 
 upon the retina. The near-point marks the limit of 
 nearness for which the lens in the eye can adapt itself. 
 In the normal eye it is about 20 centimeters frflnthe 
 eye. In Fig. 5, jj represents the pin-point and r its 
 
 r:i-^- r' 
 
 Fig. 5. 
 
 image upon the retina. If the pin-point be brought 
 nearer than the near-point of the eye, say to p, the rays 
 from it, if continued, would come to a focus back of the 
 retina at r' and would form a diffusion circle where the 
 pencil ^V pierces the retina. This diffusion circle 
 corresponds to the blur which you observed when the pin 
 was too near. We can see objects clearly only when 
 they lie at or beyond the near-point. 
 
 Xear-sighted persons also have a far-point beyond 
 which objects blur because the lens cannot adapt itself 
 to that distance. But, in the normal eye, this point is at 
 infinite distance; i.e., the eye can accommodate for 
 
VISUAL SPACE 47 
 
 parallel rays. The range between the near-point and 
 the far-point is called the range of accommodation. 
 
 h. Line of Accommodation. — Pierce two pinholes, 
 about 1 millimeter apart, in a card. Stick two pins 
 through a sheet of paper, 20 centimeters apart. Cover 
 one eye and hold the card close in front of the other eye 
 so that the two holes are in a horizontal position and fall 
 within the circumference of the pupil; hold the paper 
 with the pins pointing upward so that the near pin 
 is 20 centimeters from the eye and the two pin-points 
 
 
 are in the same line of regard. Observe that, when 
 you accommodate for the near pin, it is clear, but the 
 distant one is double ; and when you accommodate for 
 the distant pin, it is clear and the near one is double. 
 Take out the distant pin and move it toward the near 
 one and find how close you must bring it before you can 
 see both clearly with a single accommodation.* Kecord 
 this distance, which is called the line of accommodation. 
 Fig. 6 represents the accommodation for the near 
 pin, and Fig. 7 the distant. Write out a full explana- 
 
 * Make sure that both holes are in front of the pupil. Work 
 with precision and a purpose and you will not strain the eye! 
 
48 
 
 VISUAL SPACE 
 
 tion of each figure, assuming that A and B represent 
 the two pins. 
 
 Strictly the eye can accommodate for only one point 
 in distance at a time. All points in front of and behind 
 that point must appear- blurred. This can be verified 
 rougldy by looking systematically with one eye along a 
 row of objects in the line of regard. Looking through 
 the two pinholes has the advantage of simplifying the 
 situation by producing two images instead of a blur. 
 If there were more holes, there would be more images. 
 
 Fig. 7. 
 
 Practically, however, the two pins may be separated 
 by a considerable distance and yet both be seen single or 
 clear with the same compromise accommodation because 
 ^'they seem clear enough."- We must therefore speak 
 of a line of accommodation ratlier than a point. We 
 can see two or more objects clearly at the same time 
 only if they lie within the line of accommodation. 
 
 4. Convergence: Double Images. — a. Doubling the 
 Distant Object. — Hold two objects such as a pen and a 
 pencil in the same line of regard, the former about 20 
 and the latter about 40 centimeters away from the eyes. 
 Fixate the point of the pen and, wdiile the eyes are thus 
 
VISUAL SPACE 49 
 
 converged, observe that you see two pencils. Close one 
 eye at a time and determine which of the double images 
 belongs to each eye. Eecord to which eye each image 
 belongs, the distance between the double images, and the 
 position of the double images with reference to the 
 actual position of the pencil. 
 
 Write explanation of Fig. 8, which illustrates this.* 
 
 Fig. 8. 
 
 Our two eyes constitute an effective mechanism for 
 the perception of distance or relief. One of the limita- 
 tions which follows from the very efficiency of the 
 mechanism is that we can see only one point in distance 
 clearly at a time ; every object nearer or farther away 
 than this point must be seen double if attended to. 
 
 * The level of the horizontal line L-R is somewhat arbitrary, 
 expect that it must lie between p and p'. If the observer had 
 not knoA\Ti the actual distance of the pencil he would probably 
 have seen it at about the same distance as the pen; but, know- 
 ing the actual distance, there is a tendency to see the double 
 images at approximately the true distance. The level chosen 
 in the diagram represents a compromise. 
 
50 VISUAL SPACE 
 
 This experiment has demonstrated that fact as regards 
 an object beyond the fixation-point. The next experi- 
 ment demonstrates it for objects nearer than the fixation- 
 point, and the experiment following that proves in a 
 most general way that all points within the line of 
 vision, which are nearer or more remote than the fixa- 
 tion-point are seen double. 
 
 b. Doubling the Near Object. — With pen and pencil 
 as before, fixate the pencil and, wdiile the eyes are thus 
 converged, observe that you see two pens. Close one eye 
 
 Fig. 9. 
 
 at a time to identify the double images and record as in 
 Exp. 4 a. Write explanation of Fig. 9, which illus- 
 trates this.* 
 
 c. Doubling of all Points except the Fixation-point. — 
 Stick a pin into a pencil at the middle, point the pencil 
 
 * The double images of objects nearer than the point of fixa- 
 tion are said to be "crossed," while those of objects beyond the 
 point of fixation are "uncrossed." Titchener gives the mnemonic: 
 "Remote regard reverses; 
 Nearer, notice, not." 
 
VISUAL SPACE 61 
 
 straight forward and fixate the pin ; observe that you see 
 two pencils forming an X, with the crossing at the pin. 
 Close one eye at a time and observe that the law of 
 crossed and imcrossed images is verified. 
 
 Practically, again, this point of clear vision in con- 
 vergence is really a line which we might by analogy call 
 the line of convergence. Experiments with fine points 
 show that within a moderately near range it is really a 
 point, for one of two pin-points will double until they 
 come together, but as we recede the possible separation 
 becomes appreciable, although the ''line of convergence" 
 is relatively much shorter than the line of accom- 
 modation. 
 
 d. Double Images in Indirect Vision. — Hold pen and 
 pencil as in Exp. 4 a; fixate the pen (near) and observe 
 how far you can move the pencil to the right from the 
 line of vision before one of the double images of the 
 pencil disappears. Kecord five trials. 
 
 It becomes more and more difficult to perceive the 
 double images as we pass the object gradually into the 
 indirect field. One of the double images can be seen 
 far beyond where the two can be seen. In this case 
 it is the right-eye image, as can be demonstrated by 
 closing one eye at a time. 
 
 e. Doubling Numerous Objects. — Double a strip of 
 paper and stick a row of five pins through it about 1 
 centimeter apart. Hold the paper in a horizontal posi- 
 tion at arm's length and at right angles to the line of re- 
 gard; fixate the eyes upon the pen-point, held midway 
 between the eyes and the pins, and count the pins. 
 Record number. 
 
52 VISUAL SPACE 
 
 All objects outside of the ''line of convergence' ' 
 double Avhen seen with both eyes.* Why, then, do we 
 see single objects in nature and elsewhere when many 
 objects outside of the line of convergence are seen at 
 the same time ? First, we pay attention to only one 
 point at a time ; the eyes shift with the greatest rapidity 
 from point to point and make snapshots which we are 
 aware of only as a composite view. Second, the utility 
 of disregarding double images has resulted in a natural 
 capacity for ''counting" only the impressions which 
 favor single vision. The fact that the single eye can 
 get a fully satisfactory image only at the fovea favors 
 this discarding of other images. And, third, a complex 
 view is never clear. 
 
 But why do we see single objects at all from two 
 images ? Like the projection of the single image (in- 
 deed it is a part of the process), the identifying of 
 images which fall upon corresponding points of the two 
 retinse has been learned through race and individual 
 experience in associating sight with touch and move- 
 ment. 
 
 /. DouhUng Complex and Large Objects. — Hold one 
 or more postage-stamps or other complex objects at 
 arm's length and observe by near fixation, as in Exp. 
 4 h, or far fixation, as in Exp. 4 a, that the whole ob- 
 jects double. Try larger objects, such as a letter or a 
 wall-picture. 
 
 * The indirect field, Exp. 4 d, is no exception, because when 
 one of the double images disappears we see only with one eye. 
 
 Of course, the doubling is always in the line of the eyes, 
 normally the horizontal — the whole paper strip doubled, but 
 lengthwise. 
 
VISUAL SPACE 53 
 
 Embody the results of these six experiments on double 
 images in binocular vision in one general law and write 
 it out. 
 
 5. Relief. — a. Similai' Images. — Look at Fig. 3, with 
 one eye at a time, and observe that the two images are 
 similar and there is no relief. 
 
 h. Disparate Images.- — Hold the closed text-book 
 erect and with the back toward you at arm's length ; look 
 at it first with one eye and then with the other and 
 observe that the two images are disparate, i.e., unlike. 
 Look with both eyes and observe that you see the book 
 in relief. 
 
 The basis for the perception of relief lies in the dis- 
 parateness of the two images. Relief is a mental syn- 
 thesis based upon two independent series of sense data 
 which become harmonized through the relief-interpreta- 
 tion. The mind interprets each image as a different 
 view of the same object. Look again at the book and 
 observe how the two disparate views supplement each 
 other, blend and are satisfied in the appropriate com- 
 bination. Knowing the character of the difference 
 between two images and the degree of convergence, we 
 can predict the relief. This is well illustrated in 
 stereoscopic vision. 
 
 6. Stereoscopic Vision. — Eoll a piece of paper into 
 a truncated cone and trim it to a diameter of 8 centi- 
 meters at the base and 2 centimeters at the frustum, and 
 make it about 6 centimeters high. Pin it together and 
 set it up about 50 centimeters away, with the frustum 
 
64 VISUAL SPACE 
 
 facing you at the level of your eyes. Look at it with 
 the two eyes alternately and observe the disparateness 
 of the two images. 
 
 Draw the diameters of the two ends, for each eye 
 separately, as they would be projected on a pane of 
 glass held about 15 centimeters in front of the eyes. 
 When this drawing is seen in a stereoscope it should 
 give the true skeleton of the cone.* 
 
 There are two fundamental conditions of stereo- 
 scopic vision : first, that the two views shall differ so 
 as to produce the appropriate disparateness in the two 
 retinal images; and, second, that the two views shall 
 be seen with the two eyes converged upon one point. 
 The drawings provide the first ; the lenses in the stereo- 
 scope, or converging for a point back of the card with- 
 out the stereoscope, provide for the second, t 
 
 * With a little practice stereoscopic views may be seen in re- 
 lief without the use of the stereoscope by merely converging the 
 eyes upon a point at a suitable distance back of the card. 
 Try it. 
 
 f One of the best elementary treatments of this topic, visual 
 space, is found in Witmer, "Analytical Psycholog}^" Ch. IV. 
 
CHAPTEE V 
 AUDITOEY SPACE 
 
 For Two* 
 There are three aspects of the problem of auditory 
 space ; namely^ direction, distance, and volume. The 
 present chapter is devoted to the problem of hearing the 
 direction of sound. 
 
 The experiments in this chapter should be helpful in 
 
 answering such questions as: Is the ear a space-sense 
 
 organ ? How do we perceive the direction of sound by 
 
 hearing ? What are some of the laws of localization ? f 
 
 Produce the sound, which is to be localized, by snap- 
 
 * These experiments must be performed at some other time 
 than during the class period, unless there is opportunity for 
 the class to scatter into different rooms or out of doors. Two 
 students must work together; the one who manipulates the ap- 
 paratus is called the experimenter, ( E ) , and the one on whom 
 the experiment is performed is called the observer, (0). Each 
 takes turn as E and for each experiment. E always keeps 
 the record obtained as experimenter; thus each preserves the 
 record of the other. O should be blindfolded and seated com- 
 fortably in such a position that he can hold his head erect and 
 steady in a given position during an experiment. 
 
 f There is difference of opinion as to whether or not the ear 
 is a space-sense organ. Those who hold that it is not a space- 
 sense organ base their opinion largely upon two anatomical facts: 
 ( 1 ) that the portion of the ear which is the organ of hearing 
 possesses no spread-out surface such that an arrangement of 
 stimulations upon it may represent the spatial relations of the 
 external world; and (2) that the ear is unprovided with a mus- 
 cular apparatus for focusing itself for different directions. In 
 these respects the ear is contrasted with the visual and tactual 
 arrangements for perception of space. 
 
 It is also well to bear in mind the chief theories of localiza- 
 
 55 
 
56 AUDITOEY SPACE 
 
 ping two coins.* Place one coin on each side of the 
 forefinger and press them together with the thumb and 
 the forefinger until they slide together with a snap. 
 Shift the coins deftly from one hand to the other and 
 avoid swaying movements of the body and rustling of 
 the garments. Stand on the side and reach out both 
 arms symmetrically. Blindfold and seat the observer. 
 
 1. Radially in the Median Plane, f — Let it be under- 
 stood that the sound may come from any of the seven 
 directions 45° apart: up, up-front, front, down-front, 
 down-back, back, and up-back, all within the median 
 plane. Produce the sound three times in each of these 
 
 tion. These may be divided into five classes: 
 
 (a) The intensity theory. The difference in the strength of 
 the sound in the two ears is the basis for the hearing of direction. 
 
 (h) The tactual theory. Sound vibrations also give rise to 
 sensations of touch, and we confuse these touch sensations with 
 sound sensations. 
 
 (c) Semicircular-canal theories. The semicircular canals in 
 the ear are special organs for the sensing of direction. 
 
 {d) Original space differences in the sensations of the two 
 ears. 
 
 (e) The intensity-quality theory. Both quality and intensity 
 aid in the perception of direction. 
 
 At the end of this chapter we shall turn back and ask which of 
 these theories has been supported. 
 
 *The following are better sources of sound if available: (1) a 
 telephone receiver in circuit with a battery and a mercury key; 
 (2) a "frog snapper" (electric supply houses, 25 cents) ; or (3) a 
 paper clip such as is used in hanging placards. 
 
 The apparatus which is used for accurate work in the labora- 
 tory is called a sound-perimeter or sound-cage. It is so con- 
 structed that the experimenter can manipulate it from one point 
 in the room without moving around. It enables him to vary the 
 direction, the distance, the kind, the strength, the pitch, and 
 the complexity of the sound; to control these conditions; and 
 to make accurate measurements. 
 
 fThe median plane is that vertical plane which, passing 
 through the body, divides it into right and left symmetrical 
 halves. 
 
AUDITOKY SPACE 57 
 
 directions, at a distance of about 50 centimeters, measur- 
 ing from the center of the head. Distribute the trials 
 approximately as they might run by chance. Eequire 
 O to say in which of the seven directions he hears the 
 sound. "^ Eecord each answer under the appropriate 
 heading in a prepared tabular form. Figure how many 
 answers out of the 21 are right, and how many are 45°, 
 90°, 135°, and 180° wrong respectively. 
 
 Exp. 1 might well have been entitled the ^^inability 
 to localize sound." The observer is very much sur- 
 prised and discouraged when he sees his record. 
 
 There are two factors in the record, the number of 
 correct localizations and the magnitude of the incorrect 
 localizations, to be considered. As there are 21 trials 
 distributed equally among 7 points, three of the locali- 
 zations would be right by pure chance. The trials are 
 not sufficiently numerous to enable us to apply the laws 
 of chance in prediction, but extensive experiments show 
 that a few more localizations than can be accounted for 
 by chance, will be right, probably less than 10 per cent. 
 On that basis, the observer might have four or five 
 correct localizations in this experiment. t 
 
 *It is of the greatest importance that O should have no other 
 means of detecting direction than by hearing. E must therefore 
 take every possible precaution to avoid giving any suggestion or 
 clue by word, situation, or movement. 
 
 Of course, the experimenter will be shrewd enough to give 
 no intimations to the observer about his errors during the prog- 
 ress of the experiment. 
 
 f If the observer gave more than one-fourth of the localizations 
 correctly, it is probable that this was due to failure on the part 
 of the experimenter to snap the coins exactly in the median plane, 
 or to eliminate accessory sounds from his own movements, breath- 
 ing, etc. Creaking sounds from the coat-sleeve are often taken 
 as a cue. 
 
58 AUDITORY SPACE 
 
 The other factor, the degree of error in the misplace- 
 ments, is equally significant. Under strict experi- 
 mental conditions the observer is almost as liable to 
 make an error of 180° as of 45° misplacement."^ 
 
 If the same stimulus is used, a person can improve 
 in this localization ; but the improvement will be almost 
 entirely lost as soon as the kind of sound and the 
 strength of sound are varied. 
 
 It is a striking fact that the observer has undue con- 
 fidence in his ability. When he said ^'up-front" he 
 heard the sound distinctly there, although it may have 
 come from any other point. This illusion of certainty 
 is characteristic of all our hearing of direction. We 
 continually either misjudge the direction, or learn the 
 direction through other means than hearing; yet we 
 have a distinct feeling that we have heard the 
 direction, t 
 
 2. Horizontally in Front — Measure the discrimi- 
 native sensibility for direction of sound in a horizontal 
 plane in front, at the level of the ears. Proceed as fol- 
 lows: Mark a stick about 50 centimeters long into 3- 
 centimeter steps, beginning at the middle, and marking 
 
 * This inability to localize sounds in the median plane was dis- 
 covered by Lord Rayleigh in 1875. The inability is peculiar to 
 this plane, and therefore has great significance as a test of 
 theories, 
 
 f Sitting near the central aisle of the Fifth Avenue Cathedral, 
 New York, and looking straight forward, it is practically im- 
 possible to tell whether the organ-tones issue from the front 
 or back of the cathedral. If we could see the organ, the matter 
 would be different. One of the reasons that this inability does 
 not disturb us much is that, when there is no correlation in the 
 other senses or in reason, we remain uncorrected in the illusion 
 of having heard the direction rightly. 
 
AUDITOKY SPACE 69 
 
 symmetrically in both directions. Seat O as in Exp. 1. 
 Hold the stick 1 meter from the center of his head, 
 directly in front, in a horizontal position, at right angles 
 to the median plane, and at the level of his ears. 
 Sound, in quick succession, two clicks — the first, or 
 standard, sound directly in front (at the middle or 0° 
 of the stick) and the second, or compared, click on either 
 side of the standard, the order of sides to be practically 
 such as would follow from chance. Require O to say 
 whether the second sound was to his right or left. Start 
 with a distance of 3 centimeters between the standard 
 and compare sounds and repeat the trials until O 
 makes a mistake or has ten successive answers right. 
 If a mistake is made, try with a distance of 6 centi- 
 meters in the same way. Continue thus, trying succes- 
 sive larger steps, increasing each time by 3 centimeters, 
 until you have reached one for which O gives ten suc- 
 cessive correct answers. Record the number of right 
 answers for each step. 
 
 3. Horizontally at the Back. — Make the same 
 
 measurement as in Exp. 2, for the symmetrical position 
 at the back of O. In this and the following experi- 
 ments, E should retain the same position, and O should 
 turn around in order to have the resonance in the room 
 constant. 
 
 4. Horizontally at the Side. — Make the same 
 measurement as in Exp. 2 for a point in the hori- 
 zontal plane at the level of the ears and 1 meter directly 
 to the right of the center of O's head. Let answer 
 ^'forward'' or '^backward.'' 
 
60 
 
 AUDITORY SPACE 
 
 5. Vertically at the Side. — From the same position 
 as in Exp. 4, but in the vertical plane, make the same 
 measurement as in Exp. 2 
 ^'down.'' 
 
 Let O answer ^'up" or 
 
 6. Introspections. — Repeat the largest step in Exp. 
 4 deliberately a number of times and allow O to study 
 and describe the subjective differences of the sounds by 
 which he judges their direction. Record in full his 
 observations on differences in intensity, quality, dis- 
 tance, tactual sensations, motor tendencies, visual 
 
 Qlfi ',5;° 
 
 0°B 15° 30 
 
 Fig. 10. 
 
 imagery, — in short, all features which seem to result 
 from change in the direction of the sound. 
 
 The last five experiments may be discussed together 
 most profitably. Fig. 10 is the record of the localiza- 
 tions of a trained observer within the right half of the 
 horizontal plane at the level of the ears. It is based 
 upon 18,000 measurements under the most favorable 
 conditions and therefore has a high degree of validity. 
 The radii show the directions and the arcs represent the 
 
AUDITORY SPACE 61 
 
 distance between the standard and the compared sound 
 which will yield 75 per cent of right judgments.* As 
 the sounds were produced 1 meter from the center of the 
 head, each degree corresponds to 17.5 millimeters. 
 Thus the curve shows a limit of .9° at 0° F (our Exp. 
 2), 1° at 0° B (our Exp. 3), and 4.5° at the right (our 
 Exp. 4). 
 
 In general, then, the law which should stand as the 
 prediction of our results is that the localization in this 
 horizontal plane is poorest at the side, improves by three 
 large steps in front and three behind in passing toward 
 the median plane ; it is about equally fine for front and 
 back, and it is more than four times as delicate for these 
 points as for the side. 
 
 Curves of this kind have been worked out for repre- 
 sentative planes in the field of space around the head. 
 The results of some of these are shown graphically in 
 Fig. 11, wdiich represents the right hemisphere. Ob- 
 serve that the first vertical at the left stands for the 
 front half of the median plane, and the first vertical at 
 the right represents the back half of the same plane, 
 and that the other vertical lines represent intervening 
 meridians at intervals of 15° on the surface of a hemi- 
 sphere centered at the observer's head and lying toward 
 
 * In laboratory experiments it is customary to use the dif- 
 ference which is calculated to yield 75 per cent of correct judg- 
 ments as the measure of the discrimination. In the present ex- 
 periments we have adopted the much higher standard of 100 per 
 cent correct judgments, partly to shorten and simplify the 
 method, and partly to avoid computations. Of course, the rec- 
 ords for our experiments will therefore be correspondingly 
 larger. They are also larger on account of the observer's lack 
 of training, but they should express the above general tendency 
 equally well. 
 
62 
 
 AUDITORY SPACE 
 
 his right."" The middle horizontal line represents the 
 one in which our Exps. 4 and 5 are located ; above and 
 
 -(> 
 
 () — () — () — ®-^^■ 
 
 ^^-^^ 
 
 <HH 
 
 
 15 30 «RF Tso 75 90R ^ /5 60 45Ra 30 ,5 
 
 i) — e — e — ^^— O— () — () — () — (^ 
 
 Fig. 11. 
 
 below this the parallel horizontal lines represent 
 meridians at the respective latitudes marked. 
 
 The little figures may be called sensory ellipses in 
 auditory space discrimination. They are constructed 
 
 *In reality these converge to one point at the top and one 
 point at the bottom ; the top and bottom lines become single points 
 within the median plane. They are projected in the present man- 
 ner in order to show the relative dimensions of the ellipses. 
 
AUDITORY SPACE 63 
 
 in the following manner: At any intersection, vertical 
 and horizontal distances are laid off on the basis of the 
 corresponding measurements. Thus, if the measure 
 of the discriminative ability is 5°, the points are laid off 
 2 1-2° below and 2 1-2° above the intersection. Two 
 points are laid off on the horizontal line on the same 
 principle. An ellipse is then constructed with these 
 points as the termini of the two diameters. 
 
 The ellipses mean that every diameter represents, on 
 the scale of the chart, the degree of separation of two 
 sounds which would yield 75 per cent correct judgments 
 of direction under the given conditions of the ex- 
 periments. * 
 
 Thus, following the middle horizontal line, 0° F, 
 0' B, and 90° R represent the points in Fig. 10 which 
 correspond to our measurements in Exps. 2, 3, and 4 
 respectively. Exp. 5 is represented on the vertical 
 axis at 90° E. This ellipse shows that at this point our 
 discrimination is keener in the horizontal direction than 
 in the vertical. 
 
 The psychologist can lay out a plot of the acoustic 
 field, represent measurements of significant distances 
 and directions upon it, trace their laws and distributions 
 and tell why the features represented have taken these 
 particular forms. And furthermore he can give his 
 chart of the acoustic field to the world as a guide in the 
 attempt to hear direction, and as a criterion of the 
 validity of purported hearing of direction. 
 
 The introspections in Exp. 6 bring out a number of 
 
 * Where there are only two dots and no ellipse, the measure 
 ments have not been made for the other diameter. 
 
64 AUDITORY SPACE 
 
 interesting subjective factors. Some of them may be 
 predicted. 
 
 The sound seems to be strongest at the aural axis. 
 This in turn makes the sounds which are at the aural 
 axis seem nearer than those which are away from it; 
 these sounds are also richer and clearer. 
 
 There is also a tendency to hear the forward sound as 
 higher and the backward sound as lower in pitch than 
 the standard sound. The most interesting and compli- 
 cated observations probably refer to misplacements: 
 the observer knows that the sound comes from a given 
 point, but he hears it in some other direction. These 
 misplacements, in a careful observer, follow definite 
 laws, which may be worked out, as many of them already 
 have been. 
 
 Most observers have distinct visual imagery for the 
 movements of the sounding body. Frequently one is 
 conscious only of this mental vision, and the sound 
 changes as interpreted in terms of sight. The observer 
 says that the sound is forward because he has a mental 
 picture of the sounding body in that position. I^early 
 all observers make automatic movements in adaptation 
 to the changes in direction of the sound, and may be 
 conscious of these movements and be guided by them 
 without being aware of their auditory basis. Mental 
 images of movement or tendencies to movement are also 
 prominent. One may detect images of strain and 
 movement which vary with the direction of the sound. 
 
 Among the numerous tendencies which affect localiza- 
 tion are the following: 
 
 There is a tendency to locate every median sound in 
 
AUDITOKY SPACE 65 
 
 the upper front quarter, by the force of habit. Like- 
 wise sounds at the level of the ears are usually mis- 
 placed upward, and sounds in the vertical plane through 
 the aural axis are usually misplaced forward. 
 
 The effect of expectation is exceedingly complicated. 
 Thus, we tend to hear a sound from the direction it is 
 expected ; but if the direction is sensibly different, there 
 is a tendency to overestimate this difference. Try it. 
 
 There is a tendency to turn the eyes in the direction 
 of attention, and this turning of the eyes influences the 
 perception of direction. 
 
 The hearing of direction is a neglected capacity. We 
 ordinarily depend upon sight ; but should the exigencies 
 of life demand it, we could improve very much in the 
 hearing of direction. 
 
 Two ears are necessary for the normal hearing of 
 direction, but certain localizations are possible with one 
 ear alone. Fig. 12 is the curve of localization, in the 
 same plane as is represented by Fig. 10, for a person 
 who hears only with the right ear. It shows that hear- 
 ing of direction is keenest opposite the ear which is 
 intact and gradually decreases both in front and behind 
 to a point of poorest hearing in a symmetrical point on 
 the other side. Thus, he detects a difference of 4° 
 opposite the good ear, but there has to be a difference of 
 21.6° opposite the deaf ear. ^Note the bearing of this 
 upon a theory. The dotted curve is a copy of Fig. 10. 
 
 It is probable that pure tones cannot be localized at 
 all by one ear alone. 
 
 Difference in the keenness of the two ears leads to 
 misplacements whenever the decline or restoration of 
 
66 
 
 AUDITOKY SPACE 
 
 hearing in one ear is sudden. When the loss or restora- 
 tion is gradual, Ave adapt ourselves to it. 
 
 There are numerous systems of confusion-points; 
 that is, two points in different quarters which have the 
 same ''local sign" so that, although far apart, the sounds 
 from these two sources cannot be distinguished. Thus 
 45° right-back and 45° right-front are often confused. 
 
 Every unnatural position of the body, or part of the 
 body, tends to produce errors in localization. For ex- 
 
 FiG. 12. 
 
 ample, if the head is turned to the right, a sound will 
 be slightly misplaced in the direction in which the head 
 is turned. 
 
 It is usually supposed that a soimd cannot be heard as 
 well from behind as from the front. But experiments 
 show that we can hear just as faint a sound from the 
 back as from the front. Still the common suj)position 
 leads to many misplacements. 
 
 Our hearing is keenest directly opposite each ear and 
 it decreases gi-adually toward the median plane both in 
 front and back. Intensity of sound may therefore be 
 
AUDITORY SPACE 67 
 
 interpreted in terms of direction; it is possible to pre- 
 dict an apparent change in direction from the mere vary- 
 ing of the intensity of the sound. 
 
 Other things being equal, the fainter sound is judged 
 to be more distant. 
 
 Timbre is the characteristic quality of a sound and 
 depends upon the presence and reinforcement of over- 
 tones. The difference between the tones of the various 
 musical instruments is chiefly a difference in timbre. 
 As a rule, the richer the tone the better it can be 
 localized. The human voice in normal speech can be 
 localized better than any other sound. The localization 
 of the sound of a tuning-fork is very much inferior to 
 that of the voice ; and some contend that a simple pure 
 tone cannot be localized at all. At any rate, the richer 
 the tone the more ''ear-marks'' of direction it can 
 have. 
 
 The longer a sound lasts within certain limits, the 
 better it is localized. 
 
 By introducing a funnel into the ear and turning it in 
 different directions, one can make the same sound seem 
 to come from different places. 
 
 The resonance and similar modifications of the sound 
 by the environment are familiar sources of disturbance 
 to localization. If the experiments are made indoors, 
 they should preferably be made near the center of a 
 relatively empty cubical room. 
 
 There are exceedingly interesting phenomena of 
 sound fusions. 'No matter how many sounds are pro- 
 duced simultaneously, no matter from what different 
 directions they may come, provided the sounds are of 
 
68 AUDITORY SPACE 
 
 the same kind and pitch, they will be heard as one. A 
 very pretty experiment is to connect two telephone re- 
 ceivers to the same tuning-fork so that the same tone 
 is produced in both receivers. The two tones will in- 
 variably be heard as one, and this one is located accord- 
 ing to definite laws. If the two receivers are pressed 
 against the ears, the fused sound will be heard at the 
 root of the tongue — a very weird experience. The laws 
 . for the localization of fused sounds are among the 
 most valuable criteria for testing a theory of sound 
 localization.^ 
 
 To revert, then, to the questions at the beginning of 
 the chapter, we may sum up the evidence in the form of 
 a reply. The following points may be considered in 
 favor of the intensity theory : 
 
 (a) The general variation in the delicacy of localiza- 
 tion ; that is, the form and distribution of the sensory 
 ellipses. 
 
 (h) The existence of confusion-points. 
 
 (c) The difficulty of localizing sounds radially in the 
 median plane. 
 
 (d) The introspections which reveal our dependence 
 upon intensity. 
 
 (e)The inferiority of monaural localization. 
 
 From experiments of this kind we may therefore 
 conclude that intensity is tlie primary factor in the local 
 sign of hearing. 
 
 But intensity operates in two distinct ways: (1) 
 through the binaural ratio and (2) through monaural 
 
 * This may be made a very effective demonstration exercise to 
 be developed by two or three members of the class. 
 
AUDITOEY SPACE 69 
 
 ratios. With two ears we get simultaneous impressions 
 in which the intensity for one ear stands in a certain 
 ratio to the intensity for the other ear. But, for each 
 ear or with a single ear, a sound in one direction has a 
 certain intensity ratio to the same sound in another 
 direction."^ 
 
 We have also found distinct evidence of another 
 factor, namely tone quality, or the modification of the 
 character of the sound by the form of the outer ear. 
 Among the evidences for this are : 
 
 (a) Complex sounds can be localized more accurately 
 than relatively pure tones. 
 
 (h) The possibility of improvement with practice, 
 especially within the median plane. 
 
 (c) The inability to localize pure tones by one ear 
 alone. 
 
 (d) The curve of monaural localization. 
 
 (e) The introspective evidences; i.e., consciousness 
 of quality difference. 
 
 Hence we shall conclude in favor of the fifth theory, 
 the intensity-quality theory : sound is localized by means 
 
 * An interesting corroboration of this twofold nature of the 
 local sign of direction of sound is found in the "teeth" of the 
 curve in Fig. 10. There are five prominent teeth, namely, 15° E,F, 
 50° RF, 90° R, 60° RB, and 25° RB. The more accurate the meas- 
 urement the more distinct these teeth become. Now, the explana- 
 tion is to be found in the fact that there is a change at these 
 points in the means of localization. At 15° RF and 25° RB there 
 is a transition from the simple balancing of the relative intensity 
 of the two ears to the recognition of quality changes for one 
 ear. At 50= RF and 00° RB there is a transition from this double 
 standard to the monaural localization on the basis of the char- 
 acter of the sound. The large peak at 90° R is due to the fact 
 that this represents a sort of zero-point for both modes of local- 
 ization. 
 
VO AUDITORY SPACE 
 
 of binaural and monaural ratios of intensity and 
 characteristic differences in quality. * 
 
 Is the ear a space-sense organ 'i It is. As we have 
 in two eyes a means for the perception of distance, we 
 have two ears for the perception of direction. We also 
 have on each side, where the two ears cannot well co- 
 operate, ear-funnels which change the quality and the 
 intensity of the sound with reference to the direction in 
 which the vibrations impinge upon one ear. 
 
 Movement, tendencies to movement, images of 
 movement, visual or auditory images, tactual sensations 
 or images, and other factors may have been observed as 
 secondary factors which influence localization. 
 
 What are some of the laws of localization? The 
 graphic representation in Fig. 11, for example, embodies 
 a whole system of laws.f 
 
 *Quality is here used in the popular sense, as synonymous 
 with timbre. Strictly, the quality of the tone is its pitch. 
 
 fA good survey of this topic is found in Pierce, ".Studies in 
 Space-perception.*' The present chapter is based mainly upon 
 Starch, "The Localization of Sound," The University of Iowa 
 Studies in Psychology, Nos. 4 and 5. 
 
CHAPTER VI 
 TACTUAL SPACE 
 
 For Two. 
 1. Tactual Localization of a Point. — Mark off an 
 
 area 50 millimeters wide and 100 millimeters long from 
 the wrist upward, on the volar (inner) surface of the 
 forearm by ink-dots at the corners of the parallelogram. 
 Make a similar plot in the note-book. Working within 
 this area, touch O, who sits with eyes closed, lightly 
 with the point of a pencil and require him to try to 
 locate this spot, eyes opened, by touching with another 
 pencil.* Mark the relative positions of the two spots 
 by dots in the note-book plot, and connect them by a 
 light line to indicate the magnitude of the error. Label 
 the dots S (stimulus) and L (location) respectively. 
 Make 15 trials. Kecord O's analysis of what con- 
 stitutes the ''local sign" — the terms in which he recog- 
 nizes the location of a touch.f 
 
 There are three factors in the record: the measure- 
 ment of accuracy of localization in terms of the magni- 
 tude of the error; the direction of the error; and the 
 analysis of the local sign. 
 
 Accuracy of localization varies for different parts of 
 the skin ; in general, the portions of the skin which are 
 
 * Keep the results secret from O. 
 
 f For definition of local sign see Ch. IV, p. 45. 
 
 71 
 
72 TACTUAL SPACE 
 
 used most in tactual perception are most sensitive. 
 Hence we find but a crude localization for the large 
 areas for which tactual localization is relatively un- 
 important, and a fine ability for those portions which 
 are small, movable, and readily accessible. This should 
 be illustrated in the chart just made by large errors in 
 that portion which is toward the middle of the forearm, 
 and small errors at or near the wrist. 
 
 The probable direction of an error is predictable ac- 
 cording to a general law ; the point touched is generally 
 misplaced toward the nearest joint or actively used por- 
 tion of the skin in the localization. This should show 
 in the chart by a tendency of the L-dots to be nearer the 
 wrist than the S-dots. The largest errors are along the 
 axis of the arm, unless the point touched is on or very 
 close to the wrist. The errors in the radial and ulnar 
 directions are small. 
 
 It is difficult to discover by introspection just what 
 constitutes the local sign. The localization of the 
 tactual impression, like the projection of the retinal 
 image, is automatic. The mode of the accompanying 
 consciousness varies for different parts of the skin and 
 with different individuals. The record might mention 
 visual imagery, association with blood-vessels, ridges, 
 wrinkles, curvatures, relative callousness of the skin, 
 tendencies to movement, etc. The following account of 
 the local sign of the skin is apposite. 
 
 "Not only is the skin, pliysiolopfically regarded, a localizing 
 organ: the organism is endowed with reflex localizing movements, 
 Tf a spot of the skin is irritated, hand or foot moves to it re- 
 flexly, in obedience to purely physiological laws. Out of this 
 nnconseioiis localization the conscious local mark arises, by the 
 following stages: (a) The movement of the hand or foot, though 
 
TACTUAL SPACE 73 
 
 reflexly set up, occasions organic sensations in the joint, tendon, 
 etc. ; so that definite groups of organic sensations become con- 
 nected with pressures upon particular parts of the body. The 
 local sign may consist, therefore, of remembered organic sensa- 
 tions. (6) The reflex movement toward the irritated spot will 
 usually be seen; so that the local sign may contain a visual sen- 
 sation, a picture of the part touched, as well as organic sensa- 
 tions, (c) The organic sensations may pass unnoticed, owing 
 to the habitual nature of the movement. The local sign of a 
 pressure will then be a sensation of a quite different order — a 
 sensation of sight. (d) Finally the visual picture itself may 
 disappear, and its place be taken by a word, the name of the 
 part of the body pressed. Often enough, when we say that we 
 remember an occurrence, we remember only the form of the 
 word which describes it. So now, when I am touched upon the 
 arm, there flashes up in my mind the word 'arm,' and this word 
 is the local sign of the pressure." — Titchener, "Outlines of Psychol- 
 ogy," p. 157. 
 
 Tactual space is inseparably bound up witb visual 
 space. In this experiment it is extremely difficult to 
 make a purely tactual localization; there is almost in- 
 variably at least a visual image of the arm and particu- 
 larly the portion stimulated. To test the effect of the 
 visual image upon the accuracy of localization, experi- 
 ments have been made upon trained observers who had 
 the power of practically inliibiting the visual images, of 
 neglecting them, or of utilizing them in locating the 
 pressure sensations. The results show much greater 
 accuracy with the employment of visual imagery than 
 without it. 
 
 Blind persons, however, who cannot rely upon the 
 visual imagery, exhibit no larger errors in localization 
 than seeing persons. This is of course due to the great 
 reliance wdiich they must place upon pressure sensa- 
 tions, and to the practice effects in delicacy of discrimi- 
 nation which follow. This would tend to show that, 
 although vision constitutes for normal persons an im 
 
74 TACTUAL SPACE 
 
 portant element in the local sign of pressure, it is not 
 an indispensable element. 
 
 The right arm and hand of the observer have been 
 used to carry the pencil in locating the pressure sensa- 
 tions. This has added a whole group of muscle sensa- 
 tions further to complicate matters. It is well known 
 that distances are not properly judged by movements of 
 the arm and hand when flexed, as required in touching 
 a part of the other arm. Much of the constant mis- 
 placement distally has been found to be due to this 
 factor. This suggests again the interconnection between 
 tactual and muscular space.^ 
 
 2. The Two-point Space Threshold. — To measure 
 the threshold of space discrimination for two points 
 upon the skin, determine the minimum distance that 
 two spots lying in the longitudinal axis of the volar 
 surface of the forearm, stimulated simultaneously, may 
 be separated and still be perceived as two. 
 
 From a calling-card cut a strip 15 millimeters wide 
 and as long as the card ; cut this diagonally. Take the 
 two triangular '^points," and improvise a pair of com- 
 passes by holding these between the thumb and first 
 finger. Set the points at the desired distance by 
 measuring on the millimeter scale. Adopt the follow- 
 ing scale of steps in separation: 1, 2, 3, 4, 7, 11, 16, 22, 
 
 * Other methods of localizing have been designed to eliminate 
 some of these complicating factors: (a) hold the pencil just 
 over the point stimulated, but do not touch the skin; (6) mark 
 the localization upon a photograph or plaster-of-Paris model of 
 the arm; (c) describe in words as nearly as possible the loca- 
 tion. These methods may be combined and other methods de- 
 rived from them. 
 
TACTUAL SPACE 75 
 
 29, 37, and 46 millimeters. Press the two points simul- 
 taneously, gently and evenly, for about 1 second and re- 
 quire O to report whether he feels one or two."^ Start 
 with the smallest step, and if O reports "One" try the 
 next larger step, and continue thus until O reports 
 "Two." With this step give successive trials, inter- 
 spersing control trials,t until O makes a mistake or has 
 perceived the two points correctly ten times in succes- 
 sion. If a mistake is made, take next higher steps in 
 order until ten successive correct judgments are given 
 on one step. Record the number of correct judgments 
 for each step tried; the last may be considered the 
 threshold required and a measure of O's power of space 
 discrimination under these conditions. 
 
 3. Relation to Direction on Limbs. — Measure, in a 
 similar manner, the two-point space discrimination with 
 the compass-points applied in a transverse direction on 
 the same region as in Exp. 2. Compare results with 
 those of Exp. 2. 
 
 4. Relation to Part of Body. — Measure the two-point 
 'space discrimination, as in Exp. 2, (1) on the tip of the 
 first finger of the left hand and (2) in a vertical line on 
 the back of the neck. Record and compare results. 
 
 * Avoid all unnecessary fatigue of the skin area selected for ex- 
 ploitation. Take great care to apply and to withdraw the two 
 points simultaneously. Do not press hard; a clearly defined 
 sensation of contact is all that is necessary. 
 
 t Control trials may be made by touching with one point only 
 in about one-third of the trials; if O answers "Two" in a control 
 trial, this is an error indicating that he has not set himself a 
 sufficiently high standard of certainty and he must be tried on 
 a next higher step. 
 
16 TACTUAL SPACE 
 
 The two-point space threshold, which is measured in 
 Exps. 2, 3, and 4, is an index to spatial sensitiveness. 
 
 Exp. 2, the results of which may seem startling to 
 the uninitiated, demonstrates the fact that the two 
 points may be separated some distance and yet be per- 
 ceived as one. This is to be explained upon the assump- 
 tion that the local signs for the two points stimulated 
 are indistinguishable and therefore there is no basis 
 for a differentiation of the impressions. The two-point 
 threshold for this direction upon the arm is large. 
 
 In Exp. 3, with a transverse direction upon the arm, 
 the threshold is smaller. This is in line with the fact, 
 found in Exp. 1, that the radial and ulnar misplace- 
 ments in localization are small. The explanation for 
 this is based in part upon the anatomical fact that the 
 pressure-spots lie closer together transversely than in a 
 longitudinal direction. 
 
 In Exp. 4 the spatial sensitiveness is found to vary 
 with the different parts of the body ; upon the fingers it 
 is very delicate, upon the neck very obtuse. The fol- 
 lowing table ^ gives a list of representative threshold 
 values for various parts of the body in longitudinal 
 direction : 
 
 Tongue-tip 1.1 m.m. 
 
 Palm side of last phalanx of finger 2.2 " 
 
 Red part of lips 4.4 " 
 
 Tip of nose 6.6 '' 
 
 Back of second phalanx of finger 11.0 " 
 
 Heel 22.0 " 
 
 Back of hand 30.8 " 
 
 Forearm 39.6 
 
 Sternum 44.0 " 
 
 Back of neck 52.8 " 
 
 Middle of back 66.0 " 
 
 * James, Psychology, Briefer Course, p. 62. 
 
TACTUAL SPACE 11 
 
 The space discrimination in any given portion of the 
 skin may be represented by so-called sensory circles, 
 more properly called sensory ellipses, on the same plan 
 as we represented auditory space discrimination in 
 Chapter V, Fig. 11. Thns, the data in this table would 
 furnish the major axes for ellipses. 
 
 The difference in distribution of the pressure end- 
 organs and nerves, the unequal amount of practice oc- 
 casioned by exposure and use of certain parts of the 
 body, and habitual protection of others by the garments, 
 are probably sufficient to account for the wide range of 
 the two-point threshold on different bodily regions. 
 
 There is a gTadual transition from oneness to twoness. 
 Titchener quotes from Henri the following introspec- 
 tions for a series of increasing distances: 
 
 1. One small sharp point. 
 
 2. A larger blunter point. 
 
 3. A small area of oval form. 
 
 4. A line. 
 
 5. Two points, near together, connected by a line of light contact. 
 
 6. Two separate points; direction of line of junction uncertain. 
 
 7. Two separate points; direction kno\Mi. 
 
 The two-point space threshold varies also under other 
 conditions. Practice reduces it ; for instance, a thresh- 
 old of 14 millimeters may after a few periods of prac- 
 tice be reduced to 5 or 6 millimeters. Practice on one 
 area also lowers the threshold for other bodily* areas ; 
 the left forearm has been stimulated and the threshold 
 for the right forearm thereby reduced from 11 to 7 
 millimeters in six practice periods. On the other hand, 
 fatigue raises the threshold; that is, it decreases the 
 sensitiveness. And drugs, such as atropine, morphine, 
 strychnine, and alcohol, have a similar effect. With 
 
78 TACTUAL SPACE 
 
 reference to temperature it may be said that if the 
 points are cold when they are applied to the skin the 
 threshold is in general lower than if the stimulus points 
 are warm : the cold points seem to be more sharply 
 localized. Warming the skin before applying the 
 points also increases the sensitiveness, while cooling the 
 skin has an opposite effect. In the experiments it is 
 best to exclude simultaneous temperature sensations. 
 Rotation of one point reduces the threshold. Disease, 
 especially of the nervous system, affects spatial sensi- 
 tiveness, sometimes increasing, sometimes decreasing it, 
 depending upon the nature of the disturbance. In some 
 diseases all pressure sensations are lost throughout more 
 or less circumscribed skin areas. Very large individual 
 differences are found among different persons, some 
 being several times more sensitive than others. 
 
 5. Simultaneous Compared with Successive Touch. 
 — Measure the two-point space discrimination in the 
 same region and in the same manner as in Exp. 2, except 
 that instead of touching the two spots simultaneously 
 you touch each with the same point quickly in succes- 
 sion. To regulate the distance, hold a ruler near the 
 skin as a guide. 
 
 When two points are applied successively instead of 
 simultaneously, as in Exp. 5, the threshold for the dis- 
 crimination of two points is very much lowered, prob- 
 ably by about one half. 
 
 Two points may be clearly perceptible as two, without 
 knowledge on the part of the observer of the direction 
 of one from the other. Two successive stimuli were 
 
TACTUAL SPACE 79 
 
 correctly perceived as two upon the forearm when 3 
 millimeters apart, but their directions were known only 
 wdien the separation was increased to 7 millimeters. 
 These figures show that the direction threshold is larger 
 than the difference or two-point threshold. The same 
 is true for simultaneous pressures. An analogous 
 tendency is also common in other sensations; for in- 
 stance, we can tell that an odor is present before we 
 can identify it, or, we may know that two tones are 
 unlike in pitch without being able to tell which is the 
 higher one. 
 
 Kelated to the comparison of simultaneous and suc- 
 cessive touch is the discrimination for the motion of a 
 point upon the skin. We can detect motion before we 
 can detect the direction of the motion. The discrimina- 
 tion for motion varies greatly with the rate of motion. 
 
 6. Method "with Knowledge" Compared with 
 Method "without Knowledge." — Kepeat Exp. 2, but 
 let O, with his eyes open, apply the compasses. Eecord 
 as before. 
 
 In this experiment we have the cooperative effect of 
 the visual, tactual, and muscular space senses; the 
 method is ^Svith knowledge" as compared with the 
 method of Exp. 2, which was "procedure without knowl- 
 edge." The two-point threshold by this method is 
 lower than when obtained by the method 'Svithout 
 knowledge." 
 
 The most effective method of securing a knowledge 
 of objects by tactual impressions is not to allow them to 
 press against the unmoved skin, but to pass the sensitive 
 skin surface over the objects and thereby gain a wealth 
 
80 TACTUAL SPACE 
 
 of information quite impossible by the passive method. 
 This is active pressure. It is keen, quick, and sure. 
 It is the method we most often employ. We do not 
 test the smoothness of a surface by simply laying the 
 hands upon it; we rub the tips of the fingers upon it. 
 The knife-grinder draws the edge of the blade he is 
 sharpening along the finger ; he does not merely hold the 
 edge of it against the finger. In active pressure the 
 skin really seems to be more sensitive ; certainly the 
 efficiency of the sensitive skin in mediating sensations 
 of the space qualities of objects is very much increased, 
 but this is really due to favorable conditions for percep- 
 tion and does not indicate any real increase in sensitive- 
 ness after all. 
 
 The blind live in a world of tactual, muscular, and 
 auditory space. Their fine space distinctions are made 
 by touch, in which they acquire most extraordinary 
 skill. A blind person can read with his finger-tips 
 almost as fast as we ordinarily read with our eyes, 
 impossible though it may seem. The print for the 
 blind consists in raised points or ridges made by em- 
 bossing a stiff paper. We experience difficulty in de- 
 tecting even the form of a single letter by touch.* 
 
 Yet the superiority of the blind in this capacity does 
 not lie so much in superior sensitivity as in the habit of 
 couching impressions in tactual terms. The two-point 
 threshold is only a trifle lower in the blind than in see- 
 
 * The style of the raised print has been improved by experi- 
 ments on the principles here studied; for example, on the rela- 
 tive legibility of a line as compared with a dot alphabet, or sim- 
 ultaneous impressions of dots compared with successive impres- 
 sions, most favorable spacing, etc. 
 
TACTUAL SPACE 81 
 
 ing persons after brief practice ; and the blind person's 
 sensitivity to pressure does not differ much from that 
 of seeing persons under careful experimental condi- 
 tions,"^ But the blind person is a "tadile.^^ He thinks 
 in terms of touch as we think in terms of sight. Tac- 
 tual discriminations therefore have immediate meaning 
 to him. The superiority of the blind in this activity 
 is not in sensation but in perception. This is a funda- 
 mental but neglected distinction. 
 
 When we read we see one word at a time by direct 
 vision, and the words around this shade off gradually in 
 indirect vision. In the same manner the blind person 
 gets a clear image of one letter or word at a time by the 
 left hand and skirmishes with the right so as to get a 
 general impression of what lies ahead. He may also 
 learn to read by word instead of letter units. 
 
 * Put a human hair 3 centimeters long on a sheet of smooth 
 glass. Lay over it a sheet of clear writing-paper and locate the 
 hair by touch. Add sheet after sheet and locate as before until 
 you come to such thickness that you cannot locate the hair by 
 touch. The greatest thickness through Avhich the hair can be 
 located correctly is a measure of the sensitivity to pressure. The 
 average person whose hands are not callous should locate the hair 
 under forty to fifty sheets of "20-pound" bond paper. A blind 
 person cannot do very much better. 
 
CHAPTEE VII 
 CUTANEOUS SENSATIONS 
 
 For One* 
 The problem is to explore, identify, and plot charts 
 of cold spots, warmth spots, pain spots, and pressure 
 spots found in the skin. 
 
 Outline four blocks, each 10 by 10 millimeters, into 2- 
 millimeter squares with pen and ink on the back of the 
 left hand. Outline a copy of each of these in the note- 
 book and label them Cold, Warmth, Pain, and Pressure 
 respectively, t 
 
 Put six of the nails on crushed ice and the other six 
 into water just below the boiling-point. t The sense- 
 organs in the skin fatigue very quickly — almost in- 
 stantaneously — when touched. Therefore, select points 
 for stimulation systematically; follow parallel lines, 
 apply the stimulus with precision and with a constant 
 vertical pressure, remove it within a second, and always 
 trust to first impressions. Make a few preliminary 
 trials for practice on some other skin area. 
 
 * Provide a dozen tenpenny wire nails, a small cork, a horse- 
 hair from the mane, warm water, and ice. 
 
 •j- Freehand ruling is accurate enough for the purpose. 
 
 I For more accurate work a pointed metal tube is kept at a 
 constant temperature by having warm or cold water at the de- 
 sired temperature How through it. Another way is to put the 
 warm water or crushed ice into a tube and change it as often as 
 necessary. 
 
CUTANEOUS SENSATIONS 83 
 
 1. Cold Spots. — With the point of a cold nail, explore 
 a plotted area of the skin systematically and mark on 
 the note-book copy of this plot the location and approxi- 
 mate area of the spots which give rise to clear and 
 localized sensations of cold.* 
 
 When the cold nail touched certain portions of the 
 skin it did not feel cold ; but at other places definite and 
 nmnistakable sensations of cold were experienced. 
 These spots may perhaps be spoken of more properly 
 as areas. 
 
 2. Warmth Spots. — Take a warm nail — as warm as 
 it can be made without making it uncomfortable to hold 
 in the hand — and survey another plotted area system- 
 atically, and mark on its copy the location and approx- 
 imate area of the spots which give rise to clear and 
 localized sensations of warmth. 
 
 The spots sensitive to warmth are more difficult to 
 find. The warmth spots are less numerous than the 
 cold, they are less sharply localized, and they seem to 
 lie deeper do^^ai in the skin than the cold spots. The 
 warmth sensations do not follow so quickly after the 
 application of the stimulus as do the cold sensations; 
 that is, there is a more appreciable latent time. The 
 area of a warmth spot usually seems larger than that of 
 a cold spot. 
 
 The kind of stimulus which can best call forth a 
 
 * Start at one side and pass by parallel lines until the whole 
 plot has been covered by point stimulations. Never retrace or 
 verify in the same sitting. Lift the nail vertically up and down 
 and touch with the very point. Change the nails as often as it 
 is necessary to keep them cold. If the spots are large and taper 
 off, this may be shown by shading on the chart. 
 
84 CUTANEOUS SENSATIONS 
 
 certain sensation is known as an adequate stimulus. 
 Thus, light-waves constitute the adequate stimulus for 
 sight sensations. The adequate stimulus for sensations 
 of cold is the cooling of the skin, or the lowering of its 
 temperature ; that for w^armth is the warming of the 
 skin, or the raising of its temperature, in other words 
 the application of radiant energy. 
 
 NTow, since the skin is not the same temperature all 
 over the body, the same object may feel warm to one 
 part and cool to another. The temperature of a given 
 portion of the skin at a given time is known as its 
 physiological zero-point. Whether or not the stimulus 
 shall excite the cold or w^armth spots depends in part 
 upon the physiological zero-point; if the stimulus is 
 slightly warmer than the skin, w^armth sensations re- 
 sult ; if it is slightly cooler, cold sensations result. 
 
 The nerve-endings in the skin which correspond to 
 the cold spots are probably separate and distinct from 
 those which correspond to the warmth spots. Each 
 temperature spot has its own nerve-fiber or group of 
 fibers which responds with its own characteristic sensa- 
 tion only ; that is, it has its own specific energy. This 
 means that even though a warm stimulus be applied 
 to a cold spot, a sensation of cold and that only, if any, 
 will result. The same principle applies to warmth 
 spots. Ordinarily only warmth spots respond to a warm 
 stimulus and cold spots to a cold stimulus, but they 
 sometimes respond to inadequate stimuli, so that a 
 neutral stimulus, say a pin, may be used to find all four 
 kinds of spots called for in this chapter. 
 
 Cold and warmth are the two qualities of temperature 
 
CUTANEOUS SENSATIONS 85 
 
 sensations. Introspection has revealed a third tem- 
 perature experience qualitatively different from cold 
 and warmth, the perception heat. Heat or hotness is 
 something distinct from mere warmth, and it is not due 
 alone to the excessive stimulation of a warmth nerve. 
 Heat is due to a fusion of cold and warmth sensations 
 aroused by the simultaneous stimulation of cold and 
 warmth nerves by rather high temperatures. That is, 
 the same stimulus, by radiation of heat or otherwise, 
 excites both cold and warmth nerves, each of which 
 responds with its specific sensation, but the complex 
 experience is neither that of cold nor of warmth but of 
 heat. 
 
 The fact of temperature spots was discovered inde- 
 pendently by Blix, Goldscheider, and Donaldson in the 
 years 1884 and 1885. It is thought that the nerve- 
 endings of Ruffini are the organs for warmth, and the 
 endings of Krause are the organs for cold.* 
 
 3. Pain Spots. — Slit the small end of the cork and 
 insert a horsehair into the slit, so that a squarely cut 
 end of the hair projects from one side about 5 milli- 
 meters, f Hold the cork firmly near the slitted end, 
 and, by pressing the hair down vertically until it begins 
 to bend, survey a third plotted area systematically and 
 mark on the copy of it the location of those spots which 
 give rise to clear and localized sensations of pain. 
 
 * See Barker, "The Nervous System." 
 
 f The bristle should project from the cork about 3 millimeters 
 if the hand is callous, or 10 millimeters if it is very sensitive. 
 Adjust the length of the hair between these two limits as re- 
 quired. The pressure exerted should be as uniform as possible. 
 
8G CUTANEOUS SENSATIONS 
 
 When the whole plot has been surveyed, verify about 
 a dozen pain spots by a single touch at each and mark 
 differences in intensity of painfulness on the scale of 
 1, 2, 3, where 1 represents the faintest and 3 the 
 strongest sensations, by connecting each spot with 
 a number in the margin, as in correcting printer's 
 proof. 
 
 Pain spots are easily located, and the pain sensations 
 are very vivid and very unlike any other cutaneous 
 sensations. The pain sensations usually give rise to 
 distinct reflex movements; indeed the movement is 
 sometimes perceived before the pain. The pain spots 
 are more numerous than even the cold spots ; and, while 
 they themselves are very sensitive, intervening skin 
 areas are usually quite angestl^^c as regards pain, some- 
 times to such a degree tha^^fceedle may be inserted 
 deeply into the skin wdthoi^»ain. The cold and 
 warmth spots are analgesic, i.^Misensitive to pain ; but 
 it is difficult to stimulate thes^Rhout at the same time 
 stimulating one of the very numerous pain spots. Pain 
 spots are to be found only upon the skin or structures 
 closely connected with it genetically. The free nerve- 
 endings in the skin are probably the end-organs of 
 pain. t 
 
 There is no single adequate stimulus for pain. Any 
 of the general classes of stimuli — mechanical, thermal, 
 chemical, electrical — will cause pain. This general 
 nature of pain stimuli is necessary from the biological 
 point of view. Pain is one of the most valuable en- 
 dowments of living organisms in enabling them to avoid 
 danger. Pain means disaster ; when an experience be- 
 
CUTANEOUS SENSATIONS 87 
 
 comes painful it means that injury may follow unless 
 there is some protective reaction. The point at which 
 experiences become painful is usually just before injury 
 is likely to result. From the point of view of evolution, 
 pain was probably the first experience to appear, be- 
 cause the most necessary. It is still the best safeguard 
 we ourselves have against bodily injury. 
 
 That pain is a special sense is a relatively recent dis- 
 covery. It was formerly thought that pain resulted 
 from the excessive stimulation of any sensory nerve. 
 Such, however, is not the case. The pain we experience 
 under the influence of a very bright light comes from 
 real pain-nerves in the eye, not from the overstimula- 
 tion of the optic nerve. The most bitter sen- 
 sations are not, in the fl|pt sense of the word, pain- 
 ful. AVhen we bear in hiind the profuse distribu- 
 tion of the pain end-brgans and the general nature 
 of pain stimuli, the above fact readily becomes intel- 
 ligible. 
 
 Our English word ''pain'' is ambiguous. We use it to 
 refer, on the one hand, to pain sensations, as in this 
 chapter ; and, on the other hand, to refer to the feeling 
 of unpleasantness."^ Now, pain sensations are nearly 
 always unpleasant, but not all unpleasant experiences 
 are painful by any means. It is exceedingly unpleasant 
 to overturn one's cup of coffee at dinner, but it is not 
 necessarily painful unless one happens to be scalded by 
 the liquid. As we have used the word pain, it has had 
 
 * The Germans have two words, "Schmerz" and "Unlust", to 
 cover the ground of our word pain. 
 
88 CUTANEOUS SENSATIONS 
 
 reference alone to a special sense of pain, with central, 
 peripheral, and connecting nervous apparatus such as 
 every other special sense possesses. 
 
 Pain sensations have only one quality, pain. The 
 various kinds of pain' we think we exj^erience, such as 
 throbbing, burning, sharp or dull pains, are due to 
 variation in attributes other than quality and to the 
 accompaniment of sensations other than pain. Thus, a 
 prick, a pinch, a toothache, and a headache differ in local 
 sign, areal distribution, intensity, duration, and com- 
 bination with other sensations, but, as pains, they all 
 have the same quality. 
 
 4. Pressure Spots. — With the same finder as in Exp. 
 3, and in the same manner, survey the plotted area and 
 mark on the copy of it the spots which give rise to clear 
 and localized sensations of pressure. Record on the 
 same plot the relative position of the nearest hair to 
 each pressure spot. 
 
 . The fourth specific cutaneous sensation is pressure. 
 Pressure spots are more numerous than cold and 
 warmth spots, but less numerous than pain spots. They 
 are distributed over the surface of the whole body and 
 extend some distance into the natural openings of the 
 body cavities. Each minute hair on the body has its 
 pressure spot, usually situated to the windward, 
 but pressure spots also occur on the hairless 
 regions. The pressure nerves, which of course are 
 distinct from the temperature and pain nerves, have a 
 specialized mode of termination in the skin, each nerve- 
 fiber bearing a little terminal bulb, such as the Pacinian 
 
CUTANEOUS SENSATIONS 89 
 
 corpuscle or the spindle of Meissner. The adequate 
 stimulus for pressure is mechanical. 
 
 Pressure sensations are of one quality only, usually 
 described as feeling like a tiny seed embedded in the 
 skin and pressed downward. Ordinarily this peculiar 
 quality is not noticed, as a number of pressure spots 
 are stimulated simultaneously, and, for the most part, 
 there are accompanying temperature and pain sen- 
 sations. 
 
 In all the above cutaneous sensations we assume that 
 the ^'spot" of a specific character is due to the presence 
 of the corresponding specific end-organ. The spot be- 
 comes an appreciable area when the taut skin sur- 
 rounding the end-organ communicates the stimulus 
 indirectly. 
 
 A few years ago a schoolboy who did not know how 
 many senses he had would have been considered a dull 
 boy. He learned on his father's knee that he had five, 
 the five gates to Milton's city of Man-soul, namely, eye- 
 gate, ear-gate, nose-gate, tongue-gate, and feel-gate. 
 To-day the professor of psychology does not know with 
 certainty how many senses he has, but he does know 
 that he has more than five — possibly twice as many as 
 he was supposed to have fifty years ago. The newer 
 senses have been discovered and explored by the 
 natural-history method followed in these experiments. 
 
 How shall we know when we come across a new 
 sense ? Among the chief criteria are the following : (1) 
 the sensation, as a conscious experience, is unlike every 
 other know^n sense quality; (2) it is objective and 
 localized, and (3) it comes through specific end-organs. 
 
90 CUTANEOUS SENSATIONS 
 
 Some psychologists and physiologists hold that hunger 
 and thirst are special senses, but the prevailing opinion 
 is that hunger and thirst fail on the first and the third 
 criteria; they can be reduced to other known sense- 
 complexes. 
 
CHAPTER Vin 
 
 WEBEK'S LAW 
 
 For Two.* 
 
 If you can just barely perceive a difference of one 
 gram added to twenty grams, what is the smallest dif- 
 ference you can perceive when added to forty grams 1 
 Eighty grams ? Two hundred grams ? 
 
 Weber's law gives the answer: ^ 'Equal difference 
 between sensations means proportional difference be- 
 tween stimuli." The ratio just posited is 1 :20 ; hence 
 2 grams added to 40 grams, 4 grams added to 80 grams, 
 and 10 grams added to 200 grams would be equally per- 
 ceptible. 
 
 This law applies in various ways in the different 
 senses. Weber first demonstrated it for the perception 
 of w^eight, and as this field presents the simplest as well 
 as the most exact conditions for measurement, we shall 
 verify and illustrate the law for lifted weights. 
 
 Specifically, this is what w^e shall try to do: Exp. 1 
 is a preliminary skirmish to determine within what 
 range of weight it wdll be most profitable to make the 
 measurement on the observer ; Exp. 2 reduces this to an 
 exact measurement; and Exp. 3 makes the same 
 measurement with doubled weight and doubled incre- 
 
 * Provide two tumblers, some medium-sized shot or small nails 
 or coins, a wad of cotton, and two small pieces of woolen cloth. 
 
 91 
 
92 WEBER'S LAW 
 
 ment. Now, if Weber's law holds, there should be 
 about the same degree of success in the discrimination 
 in Exps. 2 and 3. 
 
 Select two ordinary tumblers of the same kind and 
 weight. A fairly heavy jelly-glass is good, but the sides 
 must slope so that the one fits snugly into the other. 
 Put a wad of cotton or soft cloth into the bottom of one. 
 Make a cushion out of three or four folds of cloth on 
 which to set the glass. 
 
 Prepare a differential weight as follows: Take a 
 quantity of small pieces of metal that are uniform in 
 weight (e.g., small coins, nails, or shot) and select Avhat 
 you judge to be about one tenth the weight of a glass. 
 Tie these into a small cloth so that this bag can be lifted 
 into the glass and out of it quickly and without sound 
 or other disturbance. 
 
 Blindfold O and let him be seated at the table with 
 the padded glass before him in such a position that he 
 can lift it conveniently and accurately by a free-arm 
 movement. Vary the weight of the glass by putting the 
 differential weight into it or taking it out for successive 
 trials. Every precaution must be taken to prevent any 
 other means of information than the actual sense of 
 weight. Use two signals : ''Keady" for the first of two 
 liftings in a comparison, and ''Now" for the second. 
 Make the time between the two liftings as short as 
 possible. Allow repetition of a trial only when the 
 observer calls for it on the ground of some specific dis- 
 turbance. Any accidental clue obtained from the ex- 
 perimenter would, of course, be such disturbance. 
 
 To determine the order in a comparison, flip a coin 
 
WEBER'S LAW 93 
 
 for each trial and put the differential weight into the 
 first lifting if head is up, or into the second if tail is up. 
 
 1. The Approximate Threshold of Discrimination 
 for Weight. — Let O lift the glass twice in close succes- 
 sion and say whether it was heavier in the first or the 
 second lifting. If O is right in more than 75 per cent 
 of a few trials, lessen the differential weight ; if he is 
 right only in much less than 75 per cent of the trials, 
 increase it. Skirmish in this way until you get such an 
 increment of the weight that O will get ahout 75 per 
 cent of the judgments right in 20 trials. Between 65 
 and 85 per cent will do. The increment thus obtained 
 is the one with which to make the more accurate 
 measurement in the next experiment. Record it in 
 terms of the number of objects (coins, nails, or shot). 
 
 The weight of an object is judged most accurately 
 when it is lifted in the most convenient position. The 
 same object appears to be heavier if gTasped lightly than 
 if grasped tightly. An object appears heavier if lifted v 
 in contact with a small area of skin than if in contact 
 with a larger area. An object appears heavier if lifted 
 with a slow movement than if lifted by a quick, but not 
 jerking, movement. A heavy weight grows heavier and 
 a light weight grows lighter when sustained undisturbed 
 in the hand. Of two equal weights lifted in succession, 
 the second appears to be the heavier. An object of 
 moderate weight appears to be heavier or lighter than it 
 really is according as a lighter or a heavier object has 
 been lifted just before. An object held in one hand 
 appears to be lighter than it really is if the other hand 
 
94 WEBER'S LAW 
 
 supports another weight or is otherwise engaged, as in 
 a gi'ip or push. Any deviation from the physiological 
 zero of temperature increases the apparent weight of 
 the object. An object appears to be heavier or lighter 
 than it really is according as the material of which it is 
 made suggests lighter or heavier weight than the actual. 
 Of two objects that are of the same weight but different 
 size, the larger appears to be the lighter when lifted. 
 
 This formidable array of assertions represents some of 
 the well-established laws of the perception of Aveight. 
 These laws must be kept clearly in mind in the per- 
 formance of a weight test in order to avoid introducing 
 errors which would result from the violation of such 
 laws. Thus, two objects which are to be compared in 
 weight by lifting must be lifted in the same position; 
 they must be gTasped with the same area of pressure, 
 and A\dth a grip j^roportional to their weights ; they must 
 be lifted at the same rate, to the same height, and be 
 sustained the same length of time; the order must be 
 alternated fairly; contrast-weight, counter-weight, or 
 division of energy must be avoided; temperature must 
 be kept constant ; the weights must appear to be made 
 of the same material and must be of the same size. 
 Violation of these principles is certain to result in error 
 and often appears in the most astonishing distortions of 
 weight. We must assume that they are eliminated in 
 the following experiments.* 
 
 *The flipping of the coin is another type of precaution. It 
 may seem useless, but it is indeed very essential in order to 
 forestall any tendency in the observer to make some inference, 
 whether true or false, as to what the next order shall be. Sup- 
 pose that the experimenter should determine the order arbitrarily, 
 
WEBER'S LAW 95 
 
 2. The Least Perceptible Difference. — With the dif- 
 ferential weight which in Exp. 1 gave the nearest to 
 75 per cent correct judgments, make 100 consecutive 
 trials. Record 1 for right or x for wrong in each trial. 
 
 3. The Least Perceptible Difference in the Double 
 Weight. — Put the glass used into the other one. 
 Double the differential weight. With this doubled 
 weight and doubled increment make 100 trials in the 
 same manner as in Exp. 2. Compare the per cent of 
 right cases in Exp. 2 and Exp. 3. If Weber's law 
 applies, the per cent of error should be approximately 
 equal in the two cases. 
 
 There are mathematical formulae by which we may 
 calculate from the above results what increment is 
 needed in order to yield any particular degree of cer- 
 tainty. It is customary to use 75 per cent of right 
 judgments as a norm or standard, as it lies half-way 
 between no knowledge and absolute certainty in this 
 method. Thus, if the glass in Exp. 2 weighs 200 grams 
 
 that is, as he felt it would run by chance, and suppose that he 
 had given the order "Second heavier" three times in succession, 
 would not the observer require more than an ordinary degree 
 of assurance before he would pronounce a fourth one also of the 
 same order? Yet according to chance, and in the flipping of 
 the coin, the number of times head has been up has not the 
 slightest influence on the next throw. On account of our com- 
 munity of ideas there is always a more or less subconscious tend- 
 ency present to anticipate the order of a so-called chance series 
 which is determined by one human will for another. 
 
 Another important variable is the bodily attitude taken by 
 the observer at the table. The attitude of attention is a bodily 
 attitude of muscular tension. If the observer rests against the 
 back of the chair he will make a much poorer record than if he 
 sits up with body erect and firm, bending his head gently toward 
 the lifting hand. 
 
96 WEBER'S LAW 
 
 and the differential weight is 12 grams, and this ratio 
 (6 :100) gives 72 per cent of right judgments; then, by 
 referring to a simple table,* we find that the increment 
 must be 14 grams in order to yield a certainty of 75 
 per cent right jiidginents. This computation is not 
 needed in the present case because we may here compare 
 the percentages directly. 
 
 Working with compact hard-rubber blocks, which are 
 more favorable than the glasses for fine discrimination, 
 the average constant for a good observer is about 1 :21:. 
 The ratio obtained in this test is probably considerably 
 larger, mainly for two reasons — the bulkiness of the 
 glass,t and the lack of practice of both experimenter and 
 observer. 
 
 Similar ratios may be worked out for different con- 
 ditions in this sense and for different senses. Each 
 individual has his own ratio, which is an expression of 
 his personal equation. 
 
 The principle of its application is illustrated in Fig. 
 13, which is drawn for the constant ratio 1 :24. 16, 25, 
 50, 64, etc., represent selected standards and .6, 1.0, 
 2.0, 2.6, etc., the respective increments that would be 
 just perceptible. 
 
 This illustration and the above experiment have 
 reference to sensation-difference. To be more specific, 
 
 * Sanford, "Experimental Psychologj^" p. 354 ; or Titchener, 
 "Experimental Psychology," Quantitative, Instructors' Manual, p. 
 288. 
 
 t The more compact the weiglit is the finer the discrimination 
 will be. The discrimination will be finer if a thick glass is used 
 rather than a thin one, because for the thin glass the bulk is pro- 
 portionally greater than the weight. Both glasses seem to be 
 lighter than they really are. 
 
WEBEK'S LAW 
 
 97 
 
 the law stated in the first paragraphs might be restated 
 thus : ^'To increase the sensation-difference in arithmet- 
 ical ratio, it is necessary to increase the stimulus-dif- 
 ference in geometrical ratio." There is a parallel aspect 
 of Weber's law which has reference in a more direct 
 way to sensation-magnitudes, greater than the least 
 perceptible: ''To increase the sensation in arithmetical 
 ratio, it is necessary to increase the stimulus in geo- 
 metrical ratio." This latter form of the law has great 
 practical significance in our classification of magnitudes 
 by sense-perception. 
 
 Fig. 13. 
 
 Suppose we have a thousand pebbles which range in 
 weight from 1 gram up to 100 grams and we are re- 
 quired to sort them into five piles, according to weight, 
 so divided that we shall be equally sure for each pile 
 that the sorting is right. If we could resort to the use 
 of accurate scales, the piles would range in arithmetical 
 ratio ; each pile would cover a range of 20 gTams. But 
 not so when we judge the weight by lifting. Weber's 
 law enables us to predict what the grouping should be. 
 
98 WEBER'S LAW 
 
 An excellent illustration of this second aspect of the 
 law is found in the astronomer's classification of the 
 stars. Stars are classified into a comparatively small 
 number of groups, usually fifteen, according to their 
 perceived magnitudes. Astronomers assume that this 
 classification follows Weber's law; namely, that the 
 physical magnitudes (the amounts of light emitted) do 
 not stand in a direct arithmetical ratio, but in a geomet- 
 rical ratio, in the grouping. Each group is supposed to 
 stand in a certain ratio in the following group, say 1 :10. 
 
 A psychologist attempted to verify this hypothesis. 
 He produced, in the psychological laboratory, artificial 
 stars whose physical magnitudes could be measured, and 
 then he grouped these empirically into '&ve groups on 
 the basis of perceived magnitude and ascertained their 
 average candle-power by physical measurements. The 
 results ran as follows : 
 
 Magnitude, or group I II III IV V 
 
 Average candle-poiver ....269 146 83 45 21 
 
 When one considers the crudeness of a measurement of 
 this kind, one feels that these results show a fair approx- 
 imation to the law.^ 
 
 Another type of demonstration of Weber's law may 
 
 * There is at least a very close analogy to Weber's law in any 
 practical grouping of the stars. Thus from Kapte^Ti's recent 
 work we learn that within a sphere the radius of which is 560 
 light-years there will be found: 
 
 times the light of our sun 
 
 1 star giving 
 
 from 100,000 
 
 to 10,000 
 
 26 stars " 
 
 10,000 
 
 " 1,000 
 
 1,300 " . •' 
 
 1,000 
 
 100 
 
 22,000 "• " 
 
 100 
 
 10 
 
 140,000 " 
 
 10 
 
 1 
 
 430,000 " 
 
 1 
 
 0.1 
 
 650,000 " 
 
 0.1 
 
 0.01 
 
WEBER'S LAW 99 
 
 be made in terms of discrimination-time ; that is, the 
 time that it takes to perceive a difference. It rests on 
 the postulate that if differences are equally difficult to 
 perceive, the discrimination-time for all such cases 
 should be the same. Take, for example, an increment 
 of one tenth on different weights. There is an ap- 
 paratus in the psychological laboratory which consists 
 of a system of weights and balances which may be 
 attached to an instrument that measures time in 
 hundredths of a second. To verify the law, we might 
 measure the discrimination-time for an increment of 
 1 gram on 10, 5 grams on 50, 9 grams on 90, etc. ; and, if 
 the law holds, the discrimination-times should be equal. 
 We may take a good illustration of the same type 
 from sight — the perception of the difference in the 
 length of lines. Suppose we have three sets of lines, 
 rig. 14, and we consider the middle one in each group 
 
 t-^-^ 
 
 Fig. 14. 
 
 the standard for that group. We see in the figure that 
 the longer and the shorter lines differ from the standard 
 by one fifth in all cases. Therefore, the difference 
 should be equally clear in all the cases, according to 
 Weber's law. To measure the discrimination-time, we 
 arrange the apparatus so that a compared line is ex- 
 hibited immediately after the standard line, and then 
 measure for each group the time it takes the observer to 
 perceive whether the compared line is longer or shorter 
 than the standard. If the law holds, other things being 
 
100 WEBER'S LAW 
 
 equal, this discrimination-time should be equal for all 
 the standards within a normal range so long as the 
 ratio is constant. 
 
 These three demonstrations of Weber's law — the ap- 
 plication to the least perceptible difference, the applica- 
 tion to the classification of larger differences in sense- 
 magnitudes, and the application to discrimination-time 
 — might be repeated in various respects for other senses. 
 
 We know this world in terms of four aspects of ex- 
 perience, which are the four attributes of sensation, 
 namely, quality, intensity, duration, and extensity. 
 Weber's law is primarily a law of the intensity of sensa- 
 tions, but it applies in some respects to each of the other 
 attributes. 
 
 It is generally conceded that the law applies approx- 
 imately to sensation-intensities in all the senses. We 
 have drawn our experimental illustrations from the 
 kinsesthetic sensations in the perception of weight. The 
 classification of the stars is an illustration from the 
 intensity of light.* 
 
 A clear case of the operation of Weber's laAv is found 
 in the intensity of sound.' It is perhaps equally rigid 
 for the intenstity of pressure sensations. It has been 
 demonstrated within a narrow range for taste and smell. 
 Although it has not been worked out fully for the 
 intensity of pain and temperature sensations, it prob- 
 ably applies, to some extent, there also. 
 
 * Fechner's cloud experiment is the classical illustration in 
 terms of the intensity of light, or brightness. It is to the effect 
 that if we look at a partly clouded sky and select a spot where 
 we can just detect a difference in the shading of the two clouds 
 by the naked eye and then look at this through darkening glasses 
 of different densities, the difference will remain equally clear. 
 
WEBER'S LAW 101 
 
 The operation of the law in the other sense-attributes 
 is not so clear. It has been demonstrated for visual 
 qualities (color), for arm-si^ace, eye-movements, the 
 duration of sounds, etc., but even where it applies to 
 sense-attributes other than intensity it has reference 
 •to sense-magnitude. 
 
 The most general evidence of the law is in terms of 
 the least perceptible difference, as in the above experi- 
 ,ments on weight-discrimination. Its application to 
 larger sense-magnitudes is always more doubtful. 
 
 The law can apply only within a middle or normal 
 • range of sensation-intensities in any sense. It does not 
 hold for very faint sensations, nor for excessively strong 
 sensations. 
 
 Much depends upon the method of the test. Thus, 
 the application of the law to lines. Fig. 14, is much more 
 likely to give a positive demonstration by the discrimi- 
 nation-time test than by the classification test ; indeed, 
 we should hardly expect any evidence of it by the classi- 
 fication method, because that method introduces factors 
 which may interfere with its operation. We must al- 
 ways bear in mind that every case of discrimination is a 
 complex operation depending upon scores of variables, 
 and the law could at best apply absolutely only to one 
 set of conditions. 
 
 The greatest gain in an experiment of this sort should 
 be in the revelation of the complexity and the interrela- 
 tions of mental laws even in such a simple operation as 
 the lifting of a weight. Such revelations help us to 
 analyze and understand our daily activities and should 
 result in greater efficiency. We follow Weber's law 
 
102 WEBER'S LAW 
 
 unconsciously in many of our well-regulated actions in 
 which we are guided by our senses. 
 
 Aside from the demonstration of Weber's law, these 
 experiments illustrate a common form of measurement 
 in all the senses; namely, the determination of the least, 
 perceptible difference (I. p. d.).^ The two most ele-« 
 nientary forms of measurement in all the senses are (1) 
 the threshold of sensitivity and (2) the /. j). d. or 
 threshold of discrimination. In measuring sensitivity 
 we determine the smallest quantity of any stimulus — a, 
 color, a pressure, an odor, a sound, etc. — that can be 
 sensed. In measuring discrimination w^e determine the^ 
 smallest increase (or decrease) that can be perceived 
 on any given strength of stimulus. The former is 
 chiefly a measure of the delicacy of the organism, while 
 the latter is chiefly a measure of the intellectual 
 capacity for using sense-differences. Thus, if one ob- 
 server obtained the discrimination ratio 1 :12 and the 
 other 1 :1S in the above test, we have in these ratios 
 a measure of the relative usefulness of the sense of 
 weight for the two persons. 
 
 The I. p. d. may be used as a sort of foot-rule in the 
 quantitative study of a great variety of processes. Thus, 
 with it, we may measure features of fatigue, rhythm, 
 attention, memory, mental development, race dif- 
 ferences, the effect of a stimulant, the power of emu- 
 lation, etc., provided always that we bear in mind that 
 in such cases we measure only one feature, the discrimi- 
 
 *The term "just noticeable difference" [j. n. d.) is often used 
 in place of I. p. d.; so also is the term "discrimination limen" 
 {d. L), many authors using the term "limen" for threshold. 
 
WEBER'S LAW 103 
 
 nation, and that our conclusions must not go beyond 
 this. To illustrate the reservation, suppose that the 
 experimenter sets himself the task of determining what 
 the mental effect of a cup of coffee is. Among other 
 measurements he may include the discrimination-tests 
 in the various senses and for different attributes in 
 each sense, and after a long series of measurements he 
 should be able to say: My discrimination in such and 
 such activities is heightened to such and such a degree 
 for such and such a period after drinking coffee, and 
 then there is a reaction which shows at such and such a 
 time in such and such a degree for such and such of the 
 activities. 
 
CHAPTEK IX 
 MENTAL IMAGES 
 
 For One. 
 
 The problem is to determine the capacity for vivid- 
 ness of mental images. In perception, which we have 
 studied so far, the object is present to sense. We see 
 the color, hear the sound, feel the cold point, etc. ; that 
 is, we refer the mental picture to its object. In 
 memory, imagination, and the various stages of think- 
 ing, the object is not present, but the mental picture is 
 present as in percei^tion, although usually less integral, 
 less vivid, less enduring, and less distinct. This mental 
 picture which re-presents the object is the mental 
 image.* 
 
 To illustrate the fact of imagery, recall your break- 
 fast-table as you sat down to it this morning. What is 
 it that you recall ? Is it merely the names for things 
 and qualities, or is it their images ? The whiteness of 
 the china and the linen, the brightness of the silver, the 
 form of the sugar-bowl, the taste, the odor, the temper- 
 ature, and the hardness or softness of the cereal, — how 
 
 * "Images, along with sensations, constitute the materials of 
 all intellectual operations; memory, reasoning, imagination, are 
 acts which consist of grouping and coordinating images, in ap- 
 prehending the relations already formed between them, and in 
 reuniting them into new relations." (Binet.) 
 
 104 
 
MENTAL IMAGES 1U5 
 
 do these arise in your memory ? Can you image only 
 in certain senses ? Or are all these experiences abstrac- 
 tions to you ? If they are, in what terms do you re- 
 member their names ? 
 
 If we could compare answers to such questions as 
 these, we should find the most astonishing individual 
 differences in capacity for types of imagery. One per- 
 son is eye-minded, another is ear-minded. One lives in 
 a world of vivid imagery, another lives in a dull and 
 somber world of vagaie abstractions and names for 
 things. One has an accurate, serviceable memory, 
 another has a '^miserable" memory. One has an apti- 
 tude for geometry, another for music. One has a 
 fertile, constructive imagination, another is as devoid 
 of imagination as a desert is devoid of vegetation. One 
 is sensitive and responsive, another is deliberate and 
 unmoved. 
 
 If we were blind, or should walk about with our eyes 
 closed, the world would be different to us from what it 
 is now. The congenitally blind person is not only de- 
 prived of the ability to see color, form, and motion, but 
 he is also deprived of the power to remember, imagine, 
 and think of colors and visual forms and movements. 
 His world is not a visible world. Similarly, the world 
 to the deaf person is a world without sound. Helen 
 Keller lives in a world in which there is neither light, 
 nor color, nor sound.* Her world is a world of touch, 
 muscle sensations, smell, taste, temperature, and pain. 
 
 * Helen Keller retained normal sensibility until she was nine- 
 teen months old, and she says: "A person who has ever seen will 
 retain images of light throughout life; sight and sound are, how- 
 ever, of little if any use to me." 
 
106 MENTAL IMAGES 
 
 Yet she lives a more intelligent and cultured life than 
 the average college graduate. 
 
 This shows what great and varied resources the mind 
 has. Our worlds of memory and imagination may be 
 built of vastly varied materials, although to serve the 
 same purpose. Miss Keller judges character by the 
 touch of the hand ; so also do many seeing persons. 
 Many persons have normal ears for hearing, but can 
 recall things heard only in terms of the other senses. A 
 comparatively small number of persons can remember 
 coffee in terms of taste and smell. 
 
 The differences we notice in the traits of individuals 
 are not due so much to differences in sensory endow- 
 ment as to differences in the endowment of capacity for 
 representing sensory experiences in realistic, efficient, 
 and economic imagery. Although Aristotle said that 
 one cannot think without a sensible image, it is only a 
 generation ago that the fact of mental imagery attracted 
 much attention. Taine, Sir Francis Galton, Fechner, 
 Charcot, and others found that they had vivid visual 
 imagery, and made investigations which revealed the 
 fact that such imagery is almost universal. These in- 
 vestigations led also to the discovery that some persons 
 have auditory imagery. Later, more general inquiry 
 revealed the fact that it is even possible to have images 
 in terms of each and all the senses. 
 
 The main body of this exercise is devoted to a test of 
 the capacity for vividness of imagery. 
 
 This is a distinct exercise in introspection. It is best 
 to keep the eyes closed as you introspect. If the ob- 
 ser\^er does not have strong imagery he may be lost in 
 
MENTAL IMAGES 107 
 
 the effort to create an image out of the retinal light. 
 To avoid this, it is best to think of the object as in a 
 distant place ; for example, the rose on the bush. 
 
 Sometimes the image comes in the most realistic 
 way when it comes without effort as a sort of a reverie 
 image which ]3asses the mental horizon. As a rule, it is 
 best not to direct the attention primarily to the detail 
 of the image, but rather to the effort to recall the fact ; 
 when the fact comes into consciousness the character 
 of the image may be observed. 
 
 Fix clearly in mind and use as consistently as pos- 
 sible the following scale of degrees of vividness : 
 
 0. 'No image at all. 
 
 1. Very faint. 
 
 2. Faint. 
 
 3. Fairly vivid. 
 
 4. Vivid. 
 
 5. Very vivid. 
 
 6. As vivid as in perception. 
 
 Answer the following questions by writing after the 
 number of the question the number which denotes the 
 degree of vividness characteristic of your image.* In- 
 
 * To some students this exercise will be entirely too easy ; to 
 others, equally bright, it will seem like an impossible task. The 
 reason for this difference lies in the fact that one person may 
 have such vivid imagery that it is as easy for him to answer 
 the first question as to say whether or not he sees a rose which 
 is held before his open eyes, while to another person the task 
 seems unreasonable, for with the best effort, he cannot see the 
 slightest evidence of any concrete image, nor does he know what 
 it is to have such an image. These are extreme types, between 
 which normal types range. The student who finds difficulty 
 should not be discouraged. The aim of this exercise is not to 
 develop imagery, but to test the actual normal capacity. 
 
108 MENTAL IMAGES 
 
 stead of taking the questions in the order given, 
 follow the order: I 1, II 1, III 1, IV 1, V 1, VI 1, 
 VII 1, VIII 1, I 2, II 2, III 2, IV 2, etc., I 3, II 3, 
 III 3, IV 3, etc. Introspective notes to supplement 
 the numerical answers are very desirable. 
 
 1. Visual. — 1. Can you image the color of — (a) 
 
 A red rose? (h) A green leaf? (c) A yellow 
 ribbon? (d) A blue sky? 
 
 2. Can you image the brightness of — (a) A white 
 
 teacup? (h) A black crow? (c) A gray 
 stone ? (d) The blade of a knife ? 
 
 3. Can you image the form of — (a) The rose? (h) 
 
 The leaf? (c) The teacup? (d) The knife? 
 
 4. Can you form a visual image of — (a) A moving 
 
 express train ? (h) Your sharpening of a pencil ? 
 (c) An up-and-down movement of your tongue ? 
 
 5. Can you image simultaneously — (a) A group of 
 
 colors in a bunch of sweet peas? (h) Colors, 
 forms, brightnesses, and movements in a land- 
 scape view ? 
 
 6. Can you compare in a visual image — (a) The 
 
 color of cream and the color of milk? (h) The 
 tint of one of your finger-nails with that of the 
 palm of your hand ? 
 
 7. Can you hold fairly constant for ten seconds — 
 
 (a) The color of the rose ? (h) The form of the 
 rose ? 
 II. Auditory. — 1. Can you image the sound of — 
 (a) The report of a gun? (h) The clinking of 
 glasses? (c) The ringing of church-bells? (d) 
 The hum of bees ? 
 
MENTAL IMAGES 109 
 
 2. Can YOU image the characteristic tone-quality of — 
 
 (a) A violin ? (h) A cello ? (c) A flute ? (d) 
 A cornet? 
 
 3. Can you repeat in auditory imagery the air of — 
 
 (a) Yankee Doodle? (h) America? 
 
 4. Can you form auditory images of the intensity of 
 
 a violin- tone — (a) very strong; (h) strong; 
 (c) weak; (d) very weak? 
 
 5. Can you form auditory imagery of the rhythm 
 
 of — (a) The snare-drum ? (h) The bass-drum ? 
 
 (c) ''Dixie/' or other air heard played? (d) 
 "Tell me not in mournful numbers" spoken by 
 yourself ? 
 
 III. Motor. — 1. Can you image, in motor terms, 
 yourself — (a) Rocking in a chair? (b) Walk- 
 ing down a stairway? (c) Biting a lump of 
 sugar? (d) Clenching your fist? 
 
 2. Does motor imagery arise in your mind when you 
 
 recall — (a) A waterfall? (h) A facial ex- 
 pression of fear ? (c) The bleating of sheep ? 
 
 (d) Two boys on a teeter-board ? 
 
 3. Aside from the actual inceptive movements, do 
 
 you get motor imagery when recalling — (a) A 
 very high tone? (b) A very low tone? (c) 
 Words like 'Taderewski/' ''bubble," "tete-a- 
 tete," "Hurrah !" ? 
 
 4. Can you form motor images of — (a) An inch? 
 
 (&) A yard? (c) A mile ? 
 
 5. Can you form a motor image of — (a) The weight 
 
 of a pound of butter? (b) Your speed in run- 
 ning a race ? (c) The speed of an arrow ? 
 
no MENTAL IMAGES 
 
 IV. Tactual. — 1. Can you form a tactual image 
 of the pressure of — (a) Velvet? (h) Smooth 
 glass? (c) Sandpaper? (<i) Mud? 
 
 2. Can you form tactual imagery of the following 
 impressions made in the palm of your hand — 
 (a) The size of a certain coin? (6) The form 
 of the same coin? (c) The direction of a 
 line traced by a pencil-point ? (d) The inter- 
 mittent touch of a vibrating body ? 
 
 8. Can you form tactual imagery of — (a) The flow 
 of water against the finger? (h) The sensation 
 from a pressure spot ? (c) The weight of a 
 particular coin in the hand ? 
 
 V. Olfactory. — 1. Can you image the odor of — • 
 
 (a) Coffee? (&) Camphor? (c) An onion? 
 (d) Apple-blossoms ? 
 2. Can you image odors from — (a) A meadow? (h) 
 A confectioner's shop ? 
 
 VI. GusTATOEY. — 1. Can you image the taste of — 
 (a) Sugar? (h) Salt? (c) Vinegar? (d) 
 Quinine ? 
 
 2. Can you image the taste of — (a) An apple? 
 (h) A chocolate cake ? ( c) Beefsteak ? 
 
 VII. Thermal. — 1. Can you image the coldness 
 of — (a) Ice cream? {h) A draught of cold 
 air? (c) The sensation from the stimulation of 
 a cold spot ? 
 
 2. Can you image the warmth of — (a) Hot tea ? (h) 
 A warm poker? (c) A warm bath ? (d) The 
 sensation from the stimulation of a warmth 
 spot? 
 
MENTAL IMAGES 
 
 111 
 
 VIII. Pain. — 1. Can you secure a sensory image 
 
 of the pain of — (a) The prick of a pin? (6) 
 
 Running your finger along the edge of a sharp 
 
 knife? (c) A toothache or headache? (d) 
 
 The stimulation of a pain spot ? 
 
 Compute the averages for all the answers in each 
 
 of the experiments I to VIII. Lay off a plot in pencil 
 
 as in Fig. 15, eight blocks long and six high, and number. 
 
 5 
 4 
 3 
 2 
 
 1 
 
 II HI 1/ V 
 
 Fig. 15. 
 
 VI VII VIII 
 
 as in this figure, where the vertical series represents the 
 scale of vividness from to 6, and the horizontal series 
 represents the senses I to VIII. Plot the averages with 
 ink in a curve as in Fig. 15.^ 
 
 Thus, we have arrived at a very simple and telling 
 graphic representation of the observer's capacity for 
 vividness of imagery. It is, of course, relative to this 
 
 *This model curve is purely arbitrary, and does not purport to 
 represent any particular type of observer. It is inserted merely to 
 show how to make the graphic representation of the results. It 
 shows an average of 4.4 for I, 1.8 for II, 3.8 for III, .8 for IV, etc. 
 
112 MENTAL IMAGES 
 
 particular set of questions ; a different set of questions 
 covering the same ground might change the curve. A 
 set of questions is legitimate only in so far as it covers 
 the principal types of imageable facts in a fair distribu- 
 tion of tests. 
 
 You are fully aware of the unreliability of the results. 
 They are unreliable for at least two reasons. First, 
 the power of imagery varies with numerous conditions 
 and attitudes. The method of measuring, crude as it is, 
 is fully fine enough to be commensurate with the con- 
 stancy of the fact tested. Second, the results are un- 
 reliable because you were untrained. This sort of 
 introspection is a severe test upon the power of dis- 
 criminative attention and is made particularly difficult 
 and uncertain for the beginner on account of the novelty 
 and complexity of the undertaking. Faithful practice 
 in the training of any particular type of imagery is 
 usually rewarded with rapid improvement and in- 
 creased confidence in judgments. The difficulties and 
 uncertainties are greatest where there is poverty of 
 imagery. 
 
 ( Such factors as vividness, stability, and integrity of 
 Jthe image do not necessarily vary together. An image 
 may be very vivid but flitting ; it may be complete but 
 faint. For a full study of the capacity the above ques- 
 tions miglit be repeated and answered in turn with 
 reference to each of the variables in the image. This 
 same exercise might be used for the determination of 
 such factors as the stability of the image, completeness 
 of the image, effort in producing it, etc. In such cases, 
 words representing stability, completeness, effort, etc., 
 
MENTAL IMAGES 113 
 
 would be substituted for the word vivid in the scale: 
 
 thus: 'No image, very fluctuating, fluctuating, fairly 
 stable, stable, very stable, as stable as in perception. 
 
 It is customary to speak of organic sensations and 
 organic images, but that is rather misleading; for we 
 then refer to sensation-complexes or perceptions. Thus, 
 the organic feeling of movement in pointing a finger 
 may be reduced to sensations of pressure and strain in 
 the joints, muscles, and tendons. Hunger may ordi- 
 narily be reduced to a complex of pressure, pain, strain, 
 and temperature. It is of course as much easier, as it 
 is more superficial, to say that one has an image of 
 hunger than to trace the pressure-pain-strain-temper- 
 ature elements in the composite image. 
 
 The sense of equilibrium is not included in the above 
 list, for the reason that it, more than any other sense, 
 acts automatically and therefore plays a very small role 
 in consciousness. 
 
 I^ormally the image is in the same sense as the 
 original experience ; for instance, the memory of a color 
 comes as a color image, the memory of pressure comes 
 as a pressure image, the memory or imagination of taste 
 comes as a taste image, and even when present, it is 
 often overshadowed by the image in another sense. But 
 this is not always so. One's memory of running blind- 
 folded may be recalled entirely in visual terms; one's 
 memory of the taste of coffee may come in no more 
 significant imagery than sight. 
 
 Dream-life is almost purely a life of imagery; and 
 dream images are for many persons as vivid as the per- 
 ceptions of waking life. They even transcend them, 
 
114 MENTAL IMAGES 
 
 for we often dream of more brilliant colors, more beauti- 
 ful harmonies, more graceful movements, than we ever 
 perceive in waking life. 
 
 Hallucinations are common occurrences, although but 
 few persons observe or report them. Who has not 
 heard a sound where there was no sound, smelled some- 
 thing where there was nothing to smell, seen something 
 where there was nothing visible ? These hallucination 
 images are often vivid ; their very vividness makes them 
 deceptive. 
 
 This test pertains merely to the capacity for imaging 
 in terms of the respective senses and does not necessarily 
 reveal the dominant type. Indeed, should the capacity 
 be limited to but one or two senses, or should there 
 be no capacity at all, the type would be determined, 
 but such a condition is not a common occurrence. We 
 not infrequently find a record for pain images as 
 high as that for color images, but this does not signify 
 that the w^orld is equally one of pain and of color 
 to the possessor of that curve ; for pains do not occur 
 so frequently as colors, and it is customary to trans- 
 late all imagery into the terms of one sense wdien- 
 ever possible. 
 
 There are numerous methods in vogue for determin- 
 ing the type of imagery. One of these is to proceed as 
 follows : 
 
 Write, in a column, a list of thirty words that give scope^ for 
 imagery in the different senses about as in ordinary conversation; 
 for example, dog, field, waves, beefsteak, sunset, war, springtime, 
 accident, apple-blossoms, desert. Cover the list with a card and 
 expose one word at a time. As soon as the word has been seen, 
 look away and note the imagery which comes to represent the 
 word and the object it denotes. Thus, the word dog may be 
 
MENTAL IMAGES 115 
 
 grasped in terms of visual, auditory, and motor images, and the 
 dog may be imaged as a baying hound close on the scent of a 
 fox, these aspects being experienced in terms of visual, audi- 
 tory, motor, tactual, and pain images respectively. The record 
 would then read: 
 
 Word. Word Image. Object Image. 
 
 Dog Visual-auditory-motor Visual-auditory-motor-tactual-pain. 
 
 If a list of siTch words is made fairly representative, 
 tlie records will furnish a basis for an estimate of the 
 relative frequency of the images of each sense, both in 
 word memory and object memory. These records may 
 be reduced to percentages. 
 
 To show the significance of the sense through which 
 the word is first received, the series should be repeated, 
 by having the words read aloud to the observer. For 
 most persons this will cause a radical change in the 
 imagery. 
 
 The type of imagery may also be determined 
 roughly from answers to questions like these : 
 
 Into what sense do you normally translate your sensory expe- 
 riences? In terms of what imagery do you normally remember a 
 person? A place? A date? An abstract quality? Can you se- 
 cure images in any other sense than sight without also having a 
 visual image? (This question may be adapted to the other 
 senses.) Do you visualize the situations as you read a story? 
 Do you find geometry difficult? Do you recall music readily? 
 Have you a good sense of rhythm? Are you moved by realistic 
 descriptions? Do you dream much and vividly? Is there any 
 sense in which you cannot recall having had a dream image? 
 Is your word imagery conspicuous and helpful? 
 
 Among the curious idiosyncrasies which come out in 
 a test like this is that of s^Tisesthesia. Some persons 
 invariably project numbers upon forms or skeletal 
 
116 MENTAL IMAGES 
 
 shapes which may be maintained constant thronghont 
 life. Others have colored hearing; when they hear 
 or remember a tone, it seems to have color. There 
 are numerous other forms of synsesthesia, and these 
 differ very much in force and complexity. Some 
 fairly well-marked form of it may be found in from 
 5 to 10 per cent of the peoj^le in a community. 
 The explanation is to be found in the fact that we 
 have a tendency to give fulness to perceptions and 
 images. Synsesthesia is simply a specialized form of 
 this tendency and should be regarded merely as a 
 habit.* 
 
 Reverie also gives opportunity for the flow of realistic 
 imagery. The procession of images moves on without 
 effort as though it were controlled by some external 
 machinery. Reverie and concentrated attention are 
 the antipodal types of normal experience. Our or- 
 dinary life is a blending of the two, and even the 
 most reflective student will find upon introspection 
 that reverie plays by far the larger part. The read- 
 ing of a passage, the solving of a problem, the ex- 
 amination of a situation, or any other such activity 
 as requires concentration of attention is accompanied 
 
 * Answers to questions like the following reveal the presence or 
 absence of the principal forms of syn?esthesia : "Do you think 
 of particular colors in connection with letters of the alphabet, 
 or numerals, or proper names, or musical sounds, or any other 
 unusual connection? Do you think of numerals or names of 
 months, days, or years, or of any series of words as arranged in 
 any particular shapes, like circles, squares, zigzags, or very long 
 lines? Do single numerals, letters, musical notes, etc., make you 
 think of different shapes? Do you especially like or dislike any 
 numerals, letters, etc. ? Do numerals, letters, etc., seem to you to 
 be like people ?" ( Calkins, American Journal of Psychology, VII. ) 
 
MENTAL IMAGES 117 
 
 by broad streams of reverie images. These irrele- 
 vant images constitute what we call distraction or 
 mind-wandering; they are often more vivid and 
 coercive than the images obtained from the object of 
 attention. 
 
 Califop,^\^---^' 
 
CHAPTEE X 
 
 ASSOCIATION 
 
 For Two* 
 The problem is to determine certain characteristics 
 of association; namely, rapidity, kind, reinforcement, 
 error, and persistence. 
 
 1. Rapidity. — Call out a key-word, for example 
 "star", and give O exactly 8 seconds, counting from 
 the moment of the giving of the key-word, in which to 
 speak as many disconnected words as he possibly can. 
 Let O write them down in a vertical column, beginning 
 with the key-word, while they are fresh in his memory. 
 Secure five records, using as many key-words, t Find 
 the total number of words in each column excluding the 
 key-word, and divide 8 by that number to get the aver- 
 age duration of each association. 
 
 This experiment might be called chain reaction in 
 free association. It has three objects: first, to secure 
 
 * Provide coins or disks for Exp. 4, and a paper bag and 
 weights for Exp. 5. 
 
 f Speed is the aim. O must not stop to consider the fitness, 
 significance, kind of association, or anything else which may im- 
 pede the rapidity of speaking. There is a great temptation to 
 hesitate. No series should be considered successful imless has 
 spoken at least six words in the allotted time. The only limita- 
 tion on words is that they shall be disconnected; that is, they 
 cannot be a sentence, a familiar list of words, a prepared list, or 
 any series of words which have a fixed connection or sequence. 
 
 118 
 
ASSOCIATION 119 
 
 lists of words under definite conditions for use in 
 the following experiments; second, to measure the 
 rapidity of association ; and third, to give a glimpse of 
 the existence and natural flow of associations. 
 
 The observer is convinced that the associations came 
 much faster than he could express them. It is equally 
 clear to him that he did not speak as fast as mere words 
 could be uttered; there was a continual groping to ex- 
 tract one out of the many more or less remotely avail- 
 able words. 
 
 An average observer should secure a list of about ten 
 words in 8 seconds ; the average time for each word 
 would then be .8 of a second. 
 
 Each word represents a complex process or act. The 
 average time of such acts varies very much with dif- 
 ferent conditions and individuals. We speak of one as 
 having a quick reaction-time, and another as having a 
 slow reaction-time. One is mentally alert, another 
 mentally sluggish, and still another is erratic. Such 
 individual differences can be measured in great detail 
 by reaction experiments in association.* 
 
 The more completely the observer followed the in- 
 structions and abandoned himself in the battle of 
 imagery, the more surprising some of the words were to 
 him. At first thought there may be neither sense nor 
 order in them. Yet every word came according to law. 
 These laws we shall now proceed to trace. 
 
 Associations are modes of connection between per- 
 
 * In the laboratory, chronoscopes are used which record the 
 time in hundredths or thousandths of a second. One single act 
 at a time is studied, and the conditions are so varied that thii 
 act may be separated into its component elements. 
 
120 ASSOCIATION 
 
 cepts, images, and ideas. There is difference of opinion 
 in regard to the number and kinds of association, but 
 this is largely a matter of how fine distinctions we wish 
 to make. For the present purpose it is convenient to 
 posit three kinds of association, namely, contiguity, 
 similarity, and contrast, which include all possible 
 kinds.'^' These three kinds of association are spoken of 
 as laws. The law of contiguity asserts that things 
 wdiich have occurred together in time or space tend to 
 recur together. The law of similarity asserts that 
 things which are alike tend to recall one another. The 
 similarity may be of any kind, — color, form, sound, 
 odor, motion, use, etc. The law of contrast asserts that 
 opposites tend to recall one another. There may be as 
 many modes of contrast as there are of similarity. The 
 use of this classification may be illustrated best by an 
 actual case. The following record was made by the 
 author when writing this section. The key-word was 
 
 "fig." 
 
 Fig "Fig suggested apple (simil.). Tree struggled to 
 
 appear as a separate word (eontig«), but finally 
 fused with apple and formed a compound word de- 
 Apple-tree noting three distinct images, — apple, tree, blossoms 
 (contig. ). The incongruity of apples and blossoms 
 on the same tree was not noted. The images of 
 flowers were soon accompanied by images of bees 
 (contig.), but as the images came much faster than 
 Honey I could speak the words, the image of honey (con- 
 
 tig.) was uppermost in consciousness before I 
 could begin to speak the next word. The image 
 of honey made me irresistibly conscious of the 
 
 * This view is most serviceable for the elementary analysis 
 of a concrete experience, regardless of what ultimate theory of 
 association one may have. Thorndike's discussion of association 
 in his "Elements of Psychology" would supplement this exercise 
 very well. 
 
ASSOCIATION 
 
 121 
 
 question why honey should have followed flower 
 (contig. ), and there came to me, as a reply, eon- 
 Juice sciousness of the fact that honey is the juice of 
 a flower (contig. and simil.). This bit of forbidden 
 reasoning, very complex, reminded me that the 
 Sweetness characteristic quality of flower-juice is sweetness 
 (simil.). (Our imagery is much richer than our 
 vocabulary, and our associations are often couched 
 in words coined at the moment to serve their pur- 
 pose, for instance 'flower-juice' , although they 
 may be of doubtful value for currency in speech.) 
 There followed a bombardment by a mob of images 
 which struggled for recognition as representatives 
 of sweet juices or extracts (simil.). The image of 
 sugar was distinctly in the foreground (simil.), 
 Malt but before I could speak, I thought of malt as an 
 extract which contains sugar (simil.). Then a 
 whole flock of extract-bottles in varied colors and 
 forms flew before my mental eye (simil.). They 
 had so equal recognition of attention that, for the 
 moment, I could not decide to discriminate in favor 
 of one or another in the group by mentioning it, 
 so I compromised by including them all and said 
 extract ( simil. by whole and part ) . But when I 
 heard the w^ord extract I thought T'll take 
 vanilla' (simil.), and saw myself seated on a high 
 chair consuming a soda in the front of a drug- 
 store with a fountain to the left, fruit-dishes to the 
 right, and in front of me a white-jacketed waiter 
 Clerk (clerk), with a supercilious air and limited brain 
 capacity. (This scene was all one composite image 
 w^hich was suggested by soda-water ( contig. ) . 
 The last-mentioned feature in this impression 
 brought a feeling of compunction which took the 
 Phrenologist form of the question, Mm I a phrenologist (simil. 
 and contr. ), that I profess to judge a man's 
 brain?' There followed a jumble of more or less 
 fragmentary images of long hair, a phrenological 
 chart, the word 'fake' , etc., but these overran the 
 time limit." 
 
 Extract 
 
 Vanilla 
 
 There are two particularly conspicuous tendencies in 
 this introspection. The first is that, although the ob- 
 server was free to use any part of speech, nouns were 
 used exclusively. The reason for this lies in the fact 
 that economy of speech has made the object-image the 
 
122 ASSOCIATION 
 
 most available antecedent to a speech-word. The ob- 
 jects, i.e., images of objects, seem to be the things in 
 consciousness. The other peculiarity is that there was 
 only one clear case of association by contrast. Contrast 
 is a principle which should be used only for effect, and 
 in the ordinary flow of images it is not frequent. 
 
 If one has a good grasp of images, they may be traced 
 in much greater detail. 
 
 2. Kinds of Association: Primary Laws. — Let O 
 trace the chain of associations in one of the lists he has 
 and write out, on the plan of the above specimen, an 
 introspection showing which of the three kinds of as- 
 sociation operated in the transition from image to 
 image.* Make the report even more detailed than the 
 model, and point out as many links of association as 
 possible among the images of which the words represent 
 only a few. 
 
 An introspection of this kind reveals to the observer 
 something of the richness and connectedness of such a 
 simple and apparently incoherent mental act. There 
 was no trouble in seeing why each word came ; there 
 was a reason for every word. The words do not express 
 the full chain of the processes, not even all the clearly 
 conspicuous images, but simply one here and there, for 
 the flow of images is more rapid than thought and in- 
 comparably more rapid than speech. There were rea- 
 sons for every image, though few can be tracd. And, 
 furthermore, the images did not stand out isolated and 
 
 * Some observers may prefer to make a new list in order to 
 have the chain of associations fresh in the mind. 
 
ASSOCIATION 123 
 
 stripped, but were supported by a background and 
 bridging material of more or less undifferentiated 
 imagery and non-integrated mental activity. There 
 was a reason for each element in this. 
 
 Two facts of most profound significance are there- 
 fore impressed upon the observer in this experiment: 
 all images flow according to law ; the number of primary 
 laws is surprisingly small. Similarity and contrast are 
 usually considered inseparable. Each of these also in- 
 volves an element of contiguity. This has led some to 
 say that there is only one law of association. But these 
 three phases vary so much in relative prominence that it 
 is helpful to trace the dominating aspect, as in this 
 experiment. 
 
 But the question arises, what determined which 
 particular image should come forth by the law of con- 
 tiguity when there was a vast number of possibilities of 
 the same kind ? Why does apple and not a score of 
 equally similar things follow fig? Or, in similarity, 
 why does sweetness suggest sugar and not one of the 
 many other sweet things ? Why does darkness suggest 
 black horse and not some of the many other dark things ? 
 The ansAvers to these questions are to be found in the 
 secondary laws which are laws of neural action or habit. 
 Four of these are: primacy, frequency, intensity, and 
 recency."^ Other things being equal, the first or 
 primary association will dominate ; other things being 
 equal, the most frequently repeated association will 
 dominate ; other things being equal, the most impressive 
 
 * Calkins, "Association", Monograph Supplement to the Psy 
 chological Review, No. 2, 1896. 
 
124 ASSOCIATION 
 
 or intense association will dominate ; other things being 
 equal, the most recent association will dominate. 
 
 These four secondary laws may operate within any of 
 the three primary; that is, contiguity, similarity, and 
 contrast. There is thus established a complex mecha- 
 nism of forces Avhich cooperate or counteract in various 
 ways and to various degrees. 
 
 We may think of the primary law^s as kinds of ties or 
 bonds for the image, and the secondary laws as power 
 applied to each tie. Each image, ordinarily has a large 
 number of ties. Usually all three kinds are repre- 
 sented, and each is supplied with more or less power. 
 The image brought up by the key-word above had a rich 
 supply of these ties. The next image which came to the 
 front came because it was, as it were, most effectively 
 tied up with the other. This is illustrated in the fol- 
 lowing introspection which is supplementary to the one 
 quoted above : 
 
 "Fig suggested apple because apple is the most common (freq.) 
 specimen of the kind of thing a fig is, a fruit. Apple suggested 
 tree because they have been experienced together frequently 
 (freq.). Tree suggested blossoms because I had been looking for 
 blossoms on the cherry trees this morning (rec. ). Blossoms sug- 
 gested bee because bees are frequently seen with blossoms and 
 their presence has an exciting interest (freq. and int.). Bee 
 suggested honey because bee and honey are thought of as cause 
 and effect (freq.). Honey suggested juice of a flower because 
 the image of honey had followed the image of flowers (rec). 
 Flower- juice suggested sweetness because sweetness is the prin- 
 cipal characteristic of flower-juice or honey (in ten. and freq.). 
 Sweetness suggested the mass of images of sweet things because 
 there is a tendency for the mind to think the abstract in terms 
 of the concrete (freq.). Sugar came to the front from these 
 because it is the commonest of sweet things ( freq. ) , Sugar sug- 
 gested malt because sugar was thought of as an extract and malt 
 is a common form of extract which contains sugar (freq.). Ex- 
 tract was present in the image of malt ( rec. and freq. ) . Vanilla 
 came to the front because it is one of the most familiar extracts 
 
ASSOCIATION 12.5 
 
 (freq. ). Vanilla suggested ice-cream soda on account of my 
 frequent choice of that flavor in soda ( freq. ) . Soda-water sug- 
 gested myself and the whole setting in the drugstore (prim, ami 
 freq.). Clerk was named from the many objects in the setting 
 because the image represented something living and active in 
 relation to m3^self ( inten. and freq. ) . Phrenologist was drawn 
 out from the situation of my judging brain capacity on account 
 of the strangeness and incongruity of the idea ( inten. ) . The 
 images came very much faster than words could be spoken, and 
 there was a distinct tendency to fit the word to the image which 
 was just coming into consciousness at the moment that I 
 could begin to articulate the next word. For this reason many 
 very strongly associated images were deprived of opportunity for 
 expression." 
 
 3. Reinforcement ; Secondary Laws. — Let O retrace 
 the chain of associations in the same list as in Exp. 2, 
 and write out an introspection showing, as in the above 
 specimen, where and how the four secondary laws, 
 primacy, frequency, intensity, and recency, operated, — 
 not only for these words, but for all the recognized 
 images which the words represent only in part. 
 
 The primary laws are qualitative ; they denote kinds 
 of association. The secondary laws are quantitative; 
 they denote force or magnitude of a quality. The two 
 invariably operate together. Had it not been for the 
 sake of clearness, the introspections of Exps. 2 and 3 
 should have been A\T:^itten out together, stating, for ex- 
 ample, that in a given instance the law of contiguity 
 operated in several directions, but a certain one of these 
 became dominant by the law of frequency. 
 
 The associations in the list quoted above were in a 
 light, agreeable vein. The observer accounts for this 
 on the ground of '^emotional congruity." Emotional 
 congruity is one of a number of so-called laws of as- 
 sociation which are neither primary nor secondary. 
 They might properly be described as unanalyzed com- 
 
126 ASSOCIATION 
 
 plexes of association. Thus, according to this law, one 
 thinks of good and pleasant things when one is well and 
 happy, and this in turn makes one better and happier; 
 when one is blue, the disagreeable things come to mind. 
 !N^ow, a state of happiness or a state of misery, if re- 
 duced to the constituent elements in so far as they are 
 cognitive, would probably resolve itself into a very 
 intricate complex of the above primary and secondary 
 laws, or laws of a similarly elementary order. 
 
 One of the easiest ways of getting material for the 
 study of images and their modes of connection is simply 
 to sit down and relax one's self and allow a passive flow 
 of imagery, as in reverie, for a few seconds, and then go 
 over it and retrace the connections. Another good way 
 is to analyze a specific act of remembering or thinking ; 
 for instance, let the observer recall his last boat-ride, or 
 answer the question ''What is courage ?" Each of these 
 instances can be reduced to a definite network of the 
 operations of these primary and secondary laws of 
 association."^ 
 
 4. Errors of Association — Take a dollar, two half- 
 dollars, two quarter-dollars, two nickels, and two 
 dimes f and arrange them edge to edge in a row, with 
 the dollar in the middle and the other coins ranging in 
 opposite directions away from the dollar in the order of 
 diminishing size. Let O take such a position that his 
 eyes are directly over the dollar, the row pointing toward 
 
 * Work out these two examples if time permits, 
 f Circles cut any size but varying in about the same proportion 
 as the coins may be used in place of the coins. 
 
ASSOCIATION 127 
 
 him, and, without sighting or measuring, straighten the 
 row of coins so that one side tangent to all the coins will 
 seem to be a straight line. When he is satisfied that 
 the line is as straight as he can make it, without sight- 
 ing or measuring, lay a straight-edge alongside and 
 measure in millimeters the amount of misplacement 
 of each coin. 
 
 The normal observer will arrange the coins so that 
 what seems to be a straight line is really a gracefully 
 curved line. The straight-edge touches only the dollar, 
 and the other coins retreat from it by distances inversely 
 proportional to their size. This is true only for the 
 normal and careful observer; an unfaithful observer 
 may read this paragraph before he performs the ex- 
 periment and try to correct for the error. 
 
 The explanation for this normal error lies in the fact 
 that when we make one judgment we are invariably 
 beset by a number of other, often irrelevant, judgments. 
 In this case the observer was asked to make one side 
 straight ; but he could not do that without having more 
 or less dimly in the background of consciousness a line 
 through the center of the coins and a line on the other 
 side of the coins. The presence of these associations 
 influenced his judgment on the straightness of the one 
 line in question. 
 
 Fig. 16 illustrates the same principle. The middle 
 sections of the five bars are parallel; they do not look 
 parallel because we cannot entirely dissociate direction 
 of the end lines from the direction of the middle 
 sections. 
 
 Normal life, in all its phases and all the degrees of its 
 
128 
 
 ASSOCIATION 
 
 complexity, is full of errors; the greatest number of 
 these are errors of association. The association need 
 not be a conscious one ; it may have been reduced to the 
 simplest law of neural habit. 
 
 Popularly we say ''I had something else on my mind." 
 Thus, in reading we read largely by the context; and 
 for this reason there are very few good proof-readers. 
 A good author may read a proof-sheet a half-dozen times 
 without noticing that a senseless word, not to speak of 
 an error in spelling, is flagTantly evident. The good 
 
 Fig. 16. 
 
 proof-reader has mastered, to a considerable extent, the 
 power of suppressing meaning-associations."^ 
 
 5. Irrepressibility of Association. — Inflate a large 
 paper bag and tie it up. Place this bag on one hand 
 of the observer and put coins, nails, or any other heavy 
 material into the other hand until O judges that the 
 weights in the two hands are equal. Let him change 
 hands and verify his judgments until he is satisfied. 
 Then weigh the bag and the coins separately and record 
 the results. 
 
 There is a general tendency toward harmony of 
 
 7 
 
 * In reading this last word in the copy, the author read it 
 'meaningless associations." 
 
ASSOCIATION 129 
 
 properties in nature. In the long run, large objects are 
 heavier than small objects. This observed fact has 
 crystallized under the principle of frequency into a 
 neural habit which acts without our attending to it. 
 This association is a very economic principle, for it 
 helps us to adjust our efforts to our tasks. Without 
 thinking of it, we make the proper differences in ad- 
 justment of muscles for the lifting of a peck of apples 
 and a bushel of apples. Now, when a large object like 
 the bag is extraordinarily light, the association causes 
 us to put forth too great effort in lifting it and this 
 maladjustment leads to underestimation of the weight 
 of the bag. Similarly, coins are small for their weight, 
 and the same association probably leads us to make too 
 delicate an adjustment for the lifting of these; this 
 maladjustment leads to an overestimation of the weight 
 of small objects. If we now compare the actual w^eight 
 of the bag with that of the coins, w^e find that the normal 
 observer has selected coins which weigh only from a half 
 to a tenth as much as the bag. Here is the real answer 
 to the old quibble : which is heavier, a pound of lead or a 
 pound of feathers ? That this illusion persists after 
 training and accurate knowledge of the actual weights 
 is an illustration of the fact that habits of association 
 continue irrepressibly in the face of sense and reason. 
 
 We have, in this and foregoing chapters, marshalled 
 before our mind's eyes the material in the structure of 
 our knowing processes. The materials are the percep- 
 tions, images, and ideas ;* the structure is their modes 
 
 * All mental life is activity ; perceptions, images, and ideas are 
 always processes. 
 
130 ASSOCIATION 
 
 of connection — the associations. But just as in a build- 
 ing the material is all there is, so here the perceptions, 
 images, and ideas constitute the mental states, the 
 cognitive life. Association merely denotes the ways in 
 which the materials are joined together in the mental 
 framework. 
 
 Education consists in the development of associations. 
 To the uneducated, the grain of sand does not suggest 
 the great number of geological forces that brought it 
 together ; it may not even suggest the economical uses to 
 which it might be put. 
 
CHAPTER XI 
 
 MEMOKY 
 
 For Two. 
 
 The problem is to determine certain factors in the 
 capacity for memorizing geometrical figures. Two 
 
 P K- 
 
 -T 
 
 T 
 
 d "V d T 
 
 Fig. 17. 
 
 r 
 
 styles of figures will be used. One the style shown in 
 Fig. 17, and the other the style shown in Fig. 18. Let 
 
 131 
 
132 MEMOEY 
 
 the first experimenter use the former style, and the 
 second the latter. As the illustrations in the book con- 
 tain the material which is to be memorized, each person 
 must refrain rigorously from examination of the 
 
 V 
 
 ^^y- 
 
 \ 
 
 V7 ^^^ X 
 
 ^^-. :s-. _A 
 
 \ 
 
 x 
 
 ^ ^v \ 
 
 Fig. 18. 
 
 material assigned to the other. This is imperative. 
 Both may proceed independently to prepare materials 
 for the experiment, as follows : 
 
 Set A : Select nine of the figures of your style and 
 draw them neatly by freehand in a single vertical col- 
 umn in your note-book. 
 
 Set B : Arrange the same nine figures, on another 
 page, into a regular parallelogram with three figures in 
 each row horizontally and vertically. 
 
MEMOKY 133 
 
 Set C : Eearrange the same nine figures, on another 
 page, into the same kind of a parallelogram but in a 
 'radically different order; leave no figures in the same 
 position as in B. 
 
 All the figures have certain features in common : * 
 each figure is composed of three lines ; the lines are all 
 straight; two lines are equally long, and the third is 
 half as long as these; the two long lines always adjoin 
 each other; the lines join either at the end or in the 
 middle; no line is crossed; no two figures are alike. 
 The angles in one style are right angles, and in the other 
 angles of 45° or the supplement of 45.° 
 
 1. Memorizing the Form of Figures. — Allow O to 
 see the figures in Set A exactly ten seconds, in a uni- 
 form and favorable position, and then let him reproduce 
 as many of these as he can, regardless of the order in 
 the column. Examine the reproduction to see if there 
 is any error or omission f and then cover it with some 
 opaque object. Show him the set again for ten seconds 
 and let him reproduce as before. Repeat this pro- 
 cedure until O has reproduced the form of all the 
 figures correctly, regardless of the order or position in 
 the column. 
 
 Check those that are right in each reproduction, and 
 
 * In verifying this refer only to the sets of figures you have 
 selected and constructed. 
 
 f After examining a reproduction, E can say only "Right" or 
 "Wrong". If any figures are wrong in form, must discover it 
 for himself. 
 
 X In case of excessive difficulty the experiment may be left iDCom« 
 plete, say at twelve trials. 
 
134 
 
 MEMOKY 
 
 write in tabular form the number of correct figures 
 for each trial. Plot a curve of the results, as in 
 Fig. 19, where the numbers at the bottom denote the 
 successive trials, and the numbers at the side denote the 
 number of figures that remain unlearned. 
 
 Let O record observations as to method of learning 
 the figures, groupings, disturbing factors, peculiar aids 
 
 9 
 8 
 
 \ 
 
 
 
 
 
 
 
 
 \ 
 
 
 
 
 
 
 
 
 7 
 6 
 5 
 4 
 
 3 
 o 
 
 \ 
 
 
 
 
 
 
 
 
 \ 
 
 
 
 
 
 
 
 
 \ 
 
 
 
 
 
 
 
 
 
 \ 
 
 
 
 
 
 
 
 
 \ 
 
 
 \ 
 
 
 
 
 
 7 
 
 
 
 
 
 \ 
 
 
 1 
 
 
 \ 
 
 12 3 4 5 6 7 8 
 
 
 
 
 
 Fig. 
 
 19. 
 
 
 
 
 such as the use of imagery schemes, etc. — in short, 
 anything which may aid in the interpretation of the 
 curve. 
 
 One of the fundamental requirements for an experi- 
 ment, as we have seen, is that the problem shall be re- 
 duced to its elements ; only one element at a time may 
 be varied, and all other elements and conditions must 
 
MEMOEY 135 
 
 be kept constant. This is an ideal which is never fully 
 attained, yet the value of an experiment may often be 
 measured or tested by this criterion. 
 
 This experiment is an illustration of a fair control of 
 conditions in a memory test. The observer started with 
 a full and adequate knowledge of certain specifications 
 as to the number, the length, the straightness, and non- 
 crossing of the lines, the adjacency of the lines, the 
 place of joining, the magnitude of the angle, the number 
 of figures, and the absence of repetition. These are all 
 features in the memorizing of the form of the figures. 
 They could be learned by accurate discrimination in 
 repeated observation, but to have left them unmentioned 
 in the present experiment would have complicated it 
 and made it practically worthless. The experiment 
 begins with the supposition that these are known ; hence 
 they are eliminated from the memory task which is 
 before the observer.* 
 
 With all these factors under control, the problem was 
 reduced to the specific task of learning the forin of the 
 figures. Other desirable features, such as the order of 
 the figures, were excluded. 
 
 Then followed the control of conditions for learning 
 and recording. The exposure of the figures was made 
 definite, — ten seconds at a time. The time of retention 
 was made definite ; the observer reproduced immedi- 
 ately. The means of verifying were limited; the ob- 
 
 * Suppose the observer had been required to learn by observa- 
 tion that every figure has three lines, and that no two figures 
 are alike, and to learn by very close discrimination that the lines 
 do not vary in length by small steps, that the angles are uniform, 
 that the place of the joint is limited, etc. He would then have 
 faced a very different problem from the present one. 
 
136 MEMORY 
 
 server had no access to the records of his foregoing 
 trials. The experimenter's approval or disapproval was 
 uniform ; the experimenter gave no clue as to which or 
 how many were wrong. The records were all preserved, 
 making it possible to trace certain peculiarities in the 
 learning process objectively. 
 
 Yet the introspective notes show that several con- 
 ditions which might have been controlled were not con- 
 trolled. For example, the observer might have been 
 instructed as to how to proceed most effectively in mode 
 of impression, grouping, classification, associating, using 
 concrete imagery, etc. He might have been warned of 
 certain avoidable difiiculties. In technical experiments 
 such factors must also be isolated and controlled. 
 There are two reasons for not attempting it here: in 
 the natural development of a problem these factors 
 come out in introspection first and are then taken into 
 consideration, one after another, as they are revealed ; 
 they are too intricate to control in the time allotted for 
 an elementary experiment. The careful observer has 
 seen the force of many of them and has mentioned them 
 in his introspections. 
 
 Closely related to these are many individual and 
 temporary conditions which never can be controlled en- 
 tirely. Among such are the fluctuations of attention, 
 peculiar associations, temperamental disqualification for 
 the task, imagery types, habits of memorizing, etc. 
 
 Thus we see in a general way how far we have suc- 
 ceeded in complying with the requirements for analysis 
 of the problem and control of its elements. The recog- 
 nition of difiiculties is the first step toward progress. 
 
MEMOEY 137 
 
 This experiment should serve two purposes: it should 
 give a glimpse of the complexity of the conditions that 
 enter into a memory test, and it should leave the im- 
 pression that with patience and skill the complex situa- 
 tion may be reduced to more elementary ones which can 
 be isolated and controlled. 
 
 2. Memorizing the Position of the Figures. — Allow 
 O to see the figures in Set B in ten-second exposures and 
 proceed as in Exp. 1, except that the task here is to 
 memorize the positions, the forms being known from 
 Exp. 1. 
 
 Check, tabulate, plot curve, and write introspections 
 as in Exp. 1. 
 
 This experiment builds upon the foregoing. The ob- 
 server acquired a definite degree of certainty in the 
 memory of the form of the figures in Exp. 1 ; he was 
 just barely able to reproduce all the forms from memory. 
 These figures, whose form was known, were redis- 
 tributed and the task was to memorize their present 
 positions. 
 
 This task was made difficult by the similarity of the 
 figures and their relative lack of immediate associations 
 or names. The figures were '^stripped" in this 
 way to secure relatively simple and homogeneous 
 material which should enable the observer to follow 
 the development of his method and to record his intro- 
 spections. 
 
 Probably the most striking fact the observer learned 
 was that he could not ^'handle" the figures without en- 
 riching them with associations in concrete imageryc 
 
138 MEMOKY 
 
 lie faced the same kind of difficulty as he would face in 
 trying to remember individually a dozen hailstones, all 
 j^erceptibly different in shape. 
 
 The observers may be divided, on the basis of these 
 two experiments, into two types: those who go about it 
 by some sort of rote method, and those who develop 
 imagery which gives them something tangible. Both 
 of these types have various subtypes, as may be seen in 
 the introspections. In general we may say that those of 
 the first type found the first experiment very difficult 
 and the second even worse ; while those of the second 
 type soon mastered the first experiment and profited 
 very much by it in the second. An important exception 
 may be noted later. 
 
 It is a well-known fact that memorizing is facilitated 
 by giving meaning to the new material. This is illus- 
 trated in the remembering of poetry, a landscape, a face, 
 an invention, a work of art, etc. Such objects are ex- 
 ceedingly rich in meaning; we cannot think of them at 
 all except in terms of certain meanings. Such material 
 is not suitable for experimental study because it is too 
 complex; there are too many possibilities and uncer- 
 tainties. 
 
 Nonsense syllables, as buk, miv, pok, dal, etc., have 
 been used extensively on account of their supposed lack 
 of meaning. But work with such syllables soon reveals 
 the fact that one cannot memorize ten of them without 
 reading into them curious, varied, and efficient associa- 
 tions or meanings. The present figures are undoubtedly 
 much freer from natural associations, yet one cannot 
 regard them without ^'feeling into them" (German, 
 
MEMORY 139 
 
 limeinf illilen) motor, visual, tactual, or other forms of 
 imagery and perceiving analogies of various sorts. 
 
 Let us notice some of the means at the command of 
 the observer of the second, the ingenious, type. He 
 may prepare for the test by fixating clearly an image 
 of the plot of positions and then number these mentally. 
 He may make one of the specifications the basis for a 
 starting-point in the grasping of a figure. Thus^ knoiK=^ — 
 ing that there is only one short line in each figure, he 
 may classify the figures with reference to the position 
 of the short line, or with reference to the type of figure 
 formed by the other two lines. He may fix in each trial 
 a group of similar figures, the easiest figures, the most 
 difiicult figures, the figures in one line, etc., and then 
 proceed systematically by concentrating on as many as 
 he can master in one exposure. He may, if he has a 
 fertile imagination, give fantastic descriptive names to 
 the figures, or make the situation dramatic* He may 
 classify the figures into the T and F types and then 
 remember them as the one or the other upturned, 
 leaning to the right, leaning forward, top and middle 
 lines interchanged, etc. He will fix the gToup grasped 
 deliberately in the reproduction so that there shall be 
 no danger of losing any part of it when he gets other 
 groups in mind. He will adhere vigorously to the 
 principle adopted, and not mix methods. 
 
 The curve of learning is probably of the same general 
 shape here as in Exp. 1. 
 
 *Thus, in the first line of forms in Fig. 18 he may see this 
 episode : The folding chair gives away ( 1 ) , the man makes a dive 
 (2), he puts the chair into a position for comfort (3), but soon 
 finds it on the floor (4). 
 
140 MEMOKY 
 
 3. Memorizing the Position of the Figures after 
 Redistribution. — Allow O to see the figures in Set C in 
 ten-second exposures and proceed as in Exp. 2. 
 
 Check, tabulate, plot curve, and Avrite introspections 
 as in Exp. 2. 
 
 The object of this experiment is to determine to what 
 extent and in what respect the observer has profited bj 
 the foregoing training. The extent of improvement is 
 shown by a comparison of the curves. The character 
 of the cause of improvement is shown in the intro- 
 spections. 
 
 Observers of the first type find this experiment, like 
 the two foregoing ones, difficult, and show but little if 
 any progress ; wdiile observers of the second type make 
 improvement and feel the task growing easier. 
 
 Those who made improvement have probably re- 
 corded that they acquired some power or insight as to 
 means of grasping the figures in the first two experi- 
 ments. They also probably acknowledge having ben- 
 efited by one or more of the suggestions in the dis- 
 cussion of Exp. 2. But the greatest gain undoubtedly 
 depends upon the fact that the observer could here 
 place the figures in terms of their position in Set B, 
 which he remembers. Thus, he may have observed at 
 once that the first is now the seventh, the seventh is 
 now the fourth, the second is now the fifth, etc. 
 
 In any or all of the experiments a person with natural 
 ability may fail to make good progress for several rea- 
 sons. He may have imdertaken to use some means 
 which are not suited to him. He may change methods 
 and thus lose both by the discarding and by the resulting 
 
MEMOKY 141 
 
 confusion. These and many like causes may account 
 for the levels and even rises in the curve at any stage. 
 They are, of course, stated in the introspections, and 
 the idiosyncrasies of the curve are to be explained 
 principally by them. 
 
 In foregoing chapters we have learned something 
 about the significance of individual differences in sensi- 
 bility, discrimination, imagery, and association. There 
 are even greater differences in memory types. One 
 person has good memory for names, another for faces, 
 another for poetry, another for geometrical figures, etc. 
 Here we have tested one narrow type of memory. The 
 observer's other memories may or may not be like it. 
 
 This experiment suggests that improvement in mem- 
 ory consists largely in learning how to observe. This 
 fact has great pedagogical and psychological signif- 
 icance. It makes psychological analysis relatively sim- 
 ple, and gives promise that a pedagogy of memory 
 may be based upon a psychology of improvement in 
 memory. 
 
 There are three general types of methods employed 
 in experiments on memory : the method of reproduction, 
 the method of identification, and the method of intro- 
 spection of the memory image. The above experiments 
 have illustrated the first. The second might be illus- 
 trated by experiments on the memory for the size of 
 circles. A standard circle is shown ; after a given time- 
 interval a compared circle which is either equal to the 
 standard or slightly different in diameter is presented, 
 and the observer is required to say whether it is equal, 
 larger, or smaller. By varying the diameter of the com- 
 
142 MEMORY 
 
 pared circles in small steps and making a large number 
 of trials it is possible to get a measure of the observer's 
 space-memory in terms of the error made. The third 
 method is really not a method of measurement, but a 
 method of controlling introspection. The observer sets 
 himself constant conditions for observation and then ob- 
 serves in repeated trials the character of the imagery 
 and other factors, much in the same way as in the above 
 introspections.^ 
 
 Memory is not a suitable title for an experimental 
 problem because the term is too comprehensive. It 
 is customary to speak of four elements in memory: 
 impression, retention, recollection, and recognition. 
 These are in turn very broad terms. Thus, we may 
 have impressions through the different senses, imagina- 
 tion, reasoning, and feeling, and all sorts of combina- 
 tions of these. AVithin one sense, the impression may 
 have reference to different attributes ; namely, quality, 
 intensity, duration, and extensity or space. 
 
 The experiment must be limited to one factor at a 
 time, as we have seen. It may be a study, e.g., of the 
 
 * Kuhlmann, American Journal of Psychology, October, 1907, 
 suggests problems from this third point of view, as follows: 
 "This general aim is threefold. First, the analysis of the mem- 
 ory consciousness into its elements. What different kinds of 
 mental imagery, what organic sensations and affective states 
 occur in the mind from the beginning to the end of the process 
 of the recall of a given thing? Secondly, the determination of 
 the function in the memory consciousness of each of these ele- 
 ments. What is the order in which they appear, of what use is 
 each in attaining the end that is desired, to wit, the reinstate- 
 ment of the imagery that is wanted and the recognition of this 
 imagery as correct or not? Thirdly, since the end product of a 
 recall process is often a memory illusion, a prominent question 
 in memory analysis is that of the nature and causes of these 
 memory illusions." 
 
MEMOEY 143 
 
 materials of impression such as tones, spoken numbers, 
 noises, colors, distances, etc. ; it may be a study of the 
 modes of impression, such as rote, logical analysis, 
 forced association, etc. ; or it may be a study of the effect 
 of repetition, length of retention, mental occupation, 
 etc. The pursuit of any of these problems will do much 
 to enrich one's conception of the orderliness, the beauty, 
 and the worth of the life of re-presentation. 
 
chapter xii 
 appekceptio:n^ 
 
 For Two. 
 Apperception is the meaning-aspect of experience. 
 It is the grasping of a new experience in terms of previ- 
 ous experience in such a way as to give it meaning and 
 clearness and to make it serviceable. Some authors 
 reduce it to ''clearest perception/' others identify it 
 with '^attention activity/' and still others look upon it 
 as a classifying or ''pigeonholing" process. It is well to 
 keep these theories in mind. But apperception is not a 
 process in itself, such as perception, memory, or feel- 
 ing; it rather designates the fusion of the presentative 
 with the representative and the relating processes and 
 all their affective and conative tendencies, in the 
 moment of a new experience."^ 
 
 1. The Meaning-tendency. — Place a drop of ink on 
 a clean sheet in the note-book, place a sheet of paper over 
 it and press gently so that the ink forms an irregular 
 blot. Make three such blots in each note-book. Let 
 
 * Presentation includes sensation and perception ; representa- 
 tion includes memory and imagination; and elaboration or the 
 relating processes include conception, judgment, and reasoning. 
 Affection has reference to feeling, and conation to will and action. 
 
 144 
 
APPERCEPTION 145 
 
 each student write for each of these six * "gobolinks" 
 a secret list (not in the note-book) of three different 
 things it might represent, giving them in the order in 
 which they are thought of, but counting only such as 
 are apt.f 
 
 When these lists have been completed, without co- 
 operation or consultation, write the two sets of answers 
 from the lists under the respective dots and observe (1) 
 that the objects suggested may be very radically dif- 
 ferent, (2) that the meaning given is related to the ob- 
 server's interests, recent experience, habits, etc., and 
 (3) that the actual physical blot seems to change with 
 the change in meaning. 
 
 The objects suggested may be widely different ; but 
 when one observer sees the other's list he is ordinarily 
 able to see the same interpretations although he had not 
 seen the slightest hint of them before. 
 
 If we had hundreds of records of this kind, it would 
 be interesting to compare them and observe how they 
 reflect the observer's interests, recent experiences, 
 habits, temperament, mental capacity, knowledge, etc. 
 
 It is most significant that the actual physical blot 
 seems to change radically as we pass from one interpre- 
 tation to another. 
 
 The object in using the ink-blots is, of course, clear ; 
 there is no intentional design in them and they are free 
 from fixed associations. They should not represent 
 anything, yet they do suggest things in terms of past 
 experience to every alert mind. The person who ap- 
 
 * Three in each note-book, 
 
 f Do not stare at the figures or search for details. 
 
146 APPEKCEPTION 
 
 plies himself to the study of these supposedly meaning- 
 less objects in a free and artistic mood gets a glimpse of 
 that tendency in human nature which justifies the poet 
 in saying 
 
 ". . . not the slightest leaf but trembling teems 
 With golden visions and romantic dreams." 
 
 The analogy between the human eye and the photo- 
 graphic camera is instructive. There is the dark 
 chamber, the sensitive film, the lens with mechanism 
 which adjusts for clearness, distance, and size, the iris 
 diaphragm, and the cap. The camera-maker simply 
 imitates nature. But if this analogy suggests to us that 
 the human eye is nothing but a living camera, it is very 
 misleading. The camera copies the object ; the human 
 eye, ^^the mind's eye," interprets the object. 
 
 All perception is inceptive interpretation. Among 
 different persons viewing the same point in a landscape 
 under exactly similar outward conditions, the botanist 
 sees the cause for the shape of the overhanging tree, the 
 artist sees effective shadows for the setting of a sketch, 
 the carpenter sees a good location for a cottage, the 
 farmer sees the rich clover going to waste, and the 
 summer girl sees the location for a romance.* 
 
 "We see things not as they are but as we are." (Patrick.) 
 
 And let a man recall what he has seen in a familiar 
 landscape as a child, as a ball-player, as a lover, as a 
 
 * Speaking of a certain ink-blot, one writer says : "To the 
 hunter it is a beaver or a woodchuck; to the naturalist, a hedge- 
 hog or a flounder, according as his mind has been most directed 
 to land animals or fish; to the mason, a trowel; to the keeper 
 of pets, an Angora cat." (Colgrove.) 
 
APPERCEPTION 147 
 
 real-estate investor, as a naturalist — in happy moods or 
 in gray moods, in company or alone. Xo matter how 
 constant the outward features, he has always seen in the 
 landscape just what it meant to hmi in the light of his 
 knoAvledge, needs, and tendencies of the moment. 
 
 All interpretation is partial. It is confined to the 
 limits of the sense-organs, the time, opportunity, and 
 inclination for detailed scrutiny, habits of inference, the 
 purpose in mind, the store of knowledge about it, etc. 
 These facts are so universal that we scarcely take 
 cognizance of them. Before the psychologist was in- 
 terested in the doctrine of apperception, schoolboys de- 
 lighted in reciting the happy story of the six blind men 
 of Indostan who went to see the elephant. The es- 
 sential lines suffice for quotation : 
 
 First blind man, falling against the elephant's side: 
 "God bless me! but this elephant 
 Is very like a wall." 
 
 Second blind man, feeling the tusk: 
 
 "This wonder of an elephant 
 Is very like a spear." 
 
 Third blind man, grasping the squirming trunk: 
 "I see", quoth he, "the elephant 
 Is very like a snake." 
 
 The fourth blind man, clasping the knee: 
 
 " 'Tis clear enough, the elephant 
 Is very like a tree." 
 
 The fifth blind man, catching the ear: 
 
 "This marvel of an elephant 
 Is very like a fan." 
 
148 APPERCEPTION 
 
 The sixth, seizing the swinging tail : 
 
 "I see", quoth he, "the elephant 
 Is very like a rope." 
 
 "And so these men of Indostan 
 Disputed loud and long, 
 Each in his own opinion 
 Exceeding stiff and strong. 
 Though each was partly in the right, 
 And all were in the wrong." 
 
 The interpretation is personal ; it is an act for itself. 
 We can never fully perceive anything without falling 
 into a cluster of associations which are peculiar to our- 
 selves. How does the salad taste ? That depends upon 
 the season, how much one has eaten, one's preference 
 for certain dressing, the stage of dyspepsia, and the 
 attitude toward the hostess and the cook. What do you 
 see in this picture ? The reflection of something in 
 yourself. It is a happy freak of nature that so many 
 men sincerely marry the ''best woman on earth," and 
 that their children are the most wonderful children in 
 the community. 
 
 Our normal interpretation is always purposive. As 
 a rule, we attend to sense impressions only in such a 
 manner as to get the needed meaning out of them. We 
 instinctively do this in the most economic way. As we 
 grow in experience we can get along with less and less of 
 the outward impression, the sensory cue. A good 
 reader will easily see only the significant words on a 
 page ; prepositions, articles, and adverbs are often sup- 
 plied from the context. When we discover that it is 
 John Smith who is approaching, we have attained to 
 certain marks of identification which suffice to give us 
 the desired information. It may be that we have seen 
 
APPERCEPTION 149 
 
 his beard, his profile, the swagger of his walk, his 
 sombrero hat, or merely a vague something in the place 
 which we knew Mr. Smith to be ; we may have heard his 
 greeting, or only the sound of his footsteps. When we 
 see a horse we do not ordinarily examine if it has four 
 legs. Many intelligent persons do not know how many 
 legs a fly has, although they have observed flies with 
 decided interest, from the point of view of comfort, a 
 thousand times. 
 
 Perception is of "^definite and probable things.'' The 
 sound of the approaching footsteps comes out from the 
 chaos of noises around and becomes something definite. 
 
 Furthermore, pictorial representations to the eye are 
 "mere suggestions." An artist can draw a human face, 
 full of expression, with half a dozen lines. The speedy 
 crayon artist can delight his audience with character 
 sketches that remind one of moving pictures. The 
 depth, the distance, the relief, the solidity, and the size 
 in a drawing have hardly any correspondence to real 
 life. Drawung is an exceedingly abbreviated code of 
 signals to the eye. Hence we have formed a habit of 
 approaching all graphic representations with a generous 
 constructive imagination. 
 
 2. Bias. — Eecord what Fig. 20 represents to you, and 
 observe the operation of the principles mentioned in 
 Exp. 1. 
 
 Which of the two possible views shall present itself 
 first depends largely upon wdiich side of the figure one 
 attempts to read meaning into. The face is of greater 
 significance than the back of the head. One person 
 
150 APPEECEPTION 
 
 sees a rabbit, another sees a duck. Fortunately in this 
 case one can accept the view of the other when it is 
 pointed out. 
 
 The thing to be emphasized is that when the object is 
 a rabbit it is a rabbit, and when it is a duck it is a duck. 
 Yet here the object consists in a rigid and clear figure on 
 the paper. Xow, when the objective marks are not so 
 rigid, as in vague sensations, indistinct images, partial 
 generalization; and when the interpretation is an ex- 
 pression of feeling or the realization of a longing, what 
 an enormous range in the possibilities of interpretation 
 
 Fig. 20. (After Jastrow.) 
 is opened ! There is abundant opportunity for bias, 
 prejudice, and old-fogy ism. 
 
 Regarding the kaleidoscopic appearances under the 
 microscope when new features are under discussion, one 
 says rabbit and another says duck. In giving testimony 
 on the incidents of a wreck, one witness maintains rab- 
 bit and another maintains duck. Is the world going- to 
 the dogs? One ssijs rabbit, another says duck. Con- 
 sidering the beauty of a painting, one says rabbit, an- 
 other says duck. Considering the future life, one says 
 rabbit, another says duck. 
 
 Like the blind men of Indostan, each can remain 
 
APPERCEPTION 151 
 
 sincere, honest, and unshaken in his convictions because 
 he is satisfied with the view he has obtained and does 
 not give the other side an opportunity to develop. One 
 approaches his object with the expectation of rabbit, 
 another with the expectation of duck. This expecta- 
 tion can in turn be traced to environment, temperament, 
 training, desire, etc. Bias is the satisfaction with a 
 partial view. Our experiment contains a simple and 
 rigid illustration. The more complex the situation is, 
 the more danger there is of warp, twist, prepossession, 
 
 o o o o o 
 
 o o o o o 
 
 o o o o o 
 
 o o o o o 
 
 o o o o o 
 
 Fig. 21. 
 
 bigotry, quirk, crotchet, whim, and other forms of 
 obliquity which may result from falling into a rut. 
 
 To become educated is to acquire the ability to put 
 oneself into the place of another. 
 
 3. Subjective Grouping. — The circles in Fig. 21 are 
 all alike and they are grouped symmetrically. Group 
 them subjectively by voluntary attention in turn as fol- 
 
152 
 
 APPEKCEPTION 
 
 lows: (1) five horizontal lines, (2) five vertical lines, 
 (3) two diagonal lines, and (4) an outside large square 
 wdth an inside small square and a circle in the center. 
 Record how these subjective gi'oupings affect the ap- 
 parent size, clearness, and spacing of the circles. 
 
 This experiment further emphasizes the fact that the 
 actual physical object seems to change as Ave ascribe 
 different meanings to it. This figure in its plainness 
 and rigidity puts the principle to a most critical test. 
 The subjective grouping unquestionably changes the ap- 
 parent spacing, clearness, and size of the circles. 
 
 The same principle is illustrated in Fig. 22. Xow it 
 is a star ; now it is a polygon with accessory points ; now 
 
 Fig. 22. 
 
 it is a figure with two sides parallel and ends feathered. 
 In each case the lines on the page look different. 
 
 4. Reversible Perspective, a. The Reversal — Look 
 for a few moments at Figs. 23, 24, and 25 in turn 
 and observe that these figures are unstable; they are 
 seen clearly and satisfactorily in a given aspect at one 
 moment, but all at once they suddenly lop over and 
 
APPERCEPTION 
 
 153 
 
 present a radically different relief."^ Record the num- 
 ber of blocks in Fig. 24. 
 
 This experiment is introduced in order to illustrate 
 how it is possible to take a given case of apperception 
 and trace it to underlying fundamental motives. There 
 is a reason for every actual apperception of an object or 
 event, no matter how bizarre it may be. It is the 
 
 Fig. 24. 
 
 business of psychology to trace such motives in order to 
 explain mental life. 
 
 These figures are not drawn in true relief; they are 
 made ambiguous so that either of two radically dif- 
 ferent views may appear. Why should they not be 
 
 * Looking at figures with one eye favors the reversal ; so does 
 also holding the figure at a distance. 
 
154 APPERCEPTION 
 
 seen as they really are — plane figures on the surface of 
 the page ? The answer is to be found in a tendency 
 whose history can be traced. Nearly all objects in which 
 we are interested have volume and relief; relief can 
 be only suggested in a drawing; hence we have formed 
 deep-rooted habits of interpreting objects as having re- 
 lief, no matter how imperfect the device for represent- 
 ing it in the drawing. 
 
 Here again it is significant that when one particular 
 view is obtained it is entirely adequate; there is no 
 
 Fig. 25. (After Walliu.) 
 
 ambiguity in the experience. Indeed, some observers 
 find difficulty in obtaining any reversal. Yet, presto! 
 there is an instantaneous and complete reorganization of 
 the figure right under the eye, as if by some magic 
 wand. As soon as the reversal has once taken place, the 
 figure continues to oscillate irresistibly. The reason 
 it may not have reversed soon after the first trial is that 
 the observer did not know what to expect to see. Now 
 
APPEKCEPTION 155 
 
 that the two views have been seen and are equally clear 
 and convincing, expectant attention favors the change. 
 
 h. The Normal Bate of Fluctuation. — Call the first 
 relief that appears ''One" and the second "Two." Let 
 O look continuously at Fig. 23 and call out "One" or 
 "Two" as the respective changes take place. Start 
 when the second-hand of your watch is at 60 and record 
 the position of the hand at each signal for two minutes. 
 Record the approximate duration of each relief in the 
 successive appearances.^ Observe Figs. 24 and 25 in 
 the same manner. 
 
 The observer has now^ completely overcome his bias. 
 He has been liberated from the attitude in which he 
 asserted that there were only six blocks and now takes a 
 more generous and enlightened view of the situation. 
 He now realizes that there are greater resources in the 
 figures than he had first credited them Avith, and per- 
 haps draws a sweeping moral as to the operation of the 
 same principles in his ordinary interpretation of people, 
 events, theories, ideals, etc. After one has once grasped 
 the truth, it will not down, but lights the way for further 
 penetration. 
 
 c. The Fastest Rate of Fluctuation. — Proceed with 
 Fig. 23 as in Exp. 4 h, but let O force the rate of change 
 as much as possible. Record the number of changes 
 and O's introspection of the effort to force the rate. 
 
 d. The Sloicest Rate of Fluctuation. — Proceed as in 
 Exp. 4 c, but let O struggle to maintain the figure in a 
 stable view. 
 
 * If no reversal takes place in the two minutes, it is because 
 did not get sufficiently familiar with the two views in Exp. 4 a. 
 
156 
 
 APPERCEPTION 
 
 The results differ with ingenuity and chance clues of 
 the observer. For some the effect of the effort is to in- 
 crease the rate of the fluctuation in both experiments ; 
 for others there may be some appreciable success both in 
 the increase and the decrease of the rate ; still others 
 may discover the secret of the reversal and be able to 
 hold or reverse at pleasure. What this secret is we shall 
 discover in the next experiment. 
 
 e. Control of the Reversal. — Observe that Fig. 26 
 may appear to represent a glass jar one moment a& seen 
 
 from above, and another as seen from below. 
 Fixate the eyes in successive trials, upon the points in 
 the edges marked A, B, R, and 8 respectively, and ob- 
 serve that the figure remains stable so long as you retain 
 a steady fixation of one of these points, and that the 
 relief is always the same for a given point. Record for 
 each point whether the top or the bottom view prevails. 
 The secret then lies in allow^ing a certain point in 
 the figure to catch and hold the eye. Fig. 26 is favor- 
 able for the demonstration of this because it is large 
 
APPERCEPTION 157 
 
 and simple enough to enable one to control the regard. 
 It is difficult to verify this principle on the smaller 
 figures which have finer patterns over which the eye 
 involuntarily wanders from one point of regard to 
 another. 
 
 The general law observed is that the point which first 
 catches the eye or tends to hold its regard is perceived 
 as a near j^art of the object. This fixes the view. 
 
 Why should the part which first catches the eye be 
 judged near ? It is a habit. Whenever we look at 
 objects, economy bids us look first at the near side, other 
 things being equal ; this has resulted in the tendency of 
 assuming that the first part seen is the near part of the 
 object. 
 
 Why should the point upon which we maintain regard 
 be judged near? It is a habit. Whenever we try to 
 see a whole complex object there is a tendency to ac- 
 commodate for a point near the center of the surface, 
 and this is, as a rule, near us; the uniformity of this 
 experience has resulted in the tendency of assuming 
 that when we regard a fairly central point in a complex 
 figure, this point is a near part of the object. 
 
CHAPTER XIII 
 
 ATTENTION 
 
 For Tioo* 
 
 In reading this paragraph your attention moves 
 from word to word, following close npon the movement 
 of the point of regard, and you are probably aw^are of 
 this movement of attention as an expression of personal 
 activity, as an advancing wave in the tide of your feel- 
 ing of interest, and as a complex of sensory impressions 
 of bodily condition and processes of adjustment. These 
 are the most direct ways in which w^e become aware of 
 it; but attention is not an activity in itself, it is not 
 essentially a feeling of interest, nor is it essentially 
 awareness of the processes of bodily accommodation. 
 Attention is the focus of consciousness as a w^hole, the 
 state or form of concentration of the seeing, thinking, 
 remembering, feeling, doing, etc., at a given moment. 
 Attention is to consciousness as the point of regard is to 
 the field of vision, the focal point. 
 
 1. Rhythm of Attention. — When O is seated with 
 eyes closed, in a quiet room, hold an open watch at such 
 a distance from his ear that he can barely hear it. At 
 a signal let him direct his attention as steadily as 
 
 * This experiment must be performed in comparative quiet, 
 which is usually best obtained in the evening. 
 
 158 
 
ATTENTION 159 
 
 possible upon the hearing of the sound for one minute 
 and, with a pencil in hand, point upward when he hears 
 the sound and downward when he does not hear it.^ 
 Following the second-hand on the watch, tap time 
 quietly in the note-book, making a dotted line, thus, 
 
 , one dot per second ; adopt tw^o levels and trace 
 
 on the upper when O points upward, and on the lower 
 wdien he points downward, like this, 
 
 Preserve and nmnber the curves as permanent 
 records. Make a table showing the number of periods 
 and the length of each period in seconds (a) for ''Sound 
 heard" and (h) for ''Sound not heard.'' Make five 
 trials. 
 
 This experiment demonstrates that attention fluc- 
 tuates and is periodic. For reasons of biological 
 economy, consciousness cannot remain focused upon a 
 single unchanging object for more than a moment at a 
 time ; the focus, i.e., the attention, is intermittent. 
 
 A liminal stimulus was chosen because it is easier to 
 observe the changes in that than in strong stimuli, 
 although the principle of fluctuation applies to both, in- 
 deed perhaps to all objects of consciousness. And the 
 sense of hearing was chosen because the stimulus can 
 be most satisfactorily controlled for that sense. In 
 
 * If the fluctuation does not occur, the watch is either too 
 near or too far away; find such a distance that it will be heard 
 about half of the time. 
 
 A common source of failure in a beginner is that he expects 
 to hear the tick at one moment as well as at another and there- 
 fore fails to observe that he does not actually hear it but merely 
 imagines that he hears it part of the time. An attentive ob- 
 server may be able to record the missing of a single tick or two. 
 
 If any wave in a curve is due to outside disturbance, discard 
 that record and try it over again. 
 
160 
 
 ATTENTION 
 
 sight, toucli, and smell the test is complicated by the 
 rapid changes of adaptation and fatigue. The most 
 satisfactory stimulus is a constant tone of medium pitch. 
 The waves of attention are not smooth. If we could 
 get a detailed record of attention to a constant stimulus 
 such as a sustained tone, a gray surface, or a uniform 
 pressure, it would probably take a form something like 
 the white surface in Fig. 27, which might represent the 
 distribution of attention for about ten seconds schemat- 
 
 FiG. 27. 
 
 ically.* Both crests and troughs are rugged. In the 
 
 case of a tone, for example, the result of a very faint 
 
 tone might be represented at the level a-a\ where the 
 
 tone is heard very faintly and only for a relatively^ short 
 
 period; the result for a stronger stimulus might be 
 
 represented at the level h-h', where the tone is clearer 
 
 and stronger and the periods of duration are relatively 
 
 longer ; while the result for a strong stimulus might be 
 
 represented at the level c-c', which indicates that the 
 
 observer has the impression of being aware of the tone 
 
 * For attention this is merely a hypothetical diagram ; actually 
 it is a photograph of the manometric tlame for a vowel. 
 
ATTENTION 161 
 
 all the time but that there is a rhythmic fluctuation in 
 its clearness and strength."^ 
 
 Probably all mental activity — sensation, discrimina- 
 tion, feeling, memory, will, etc. — is rhythmic. The two 
 waves in Fig. 27 are made up of smaller waves, and 
 these in turn of still smaller ones. Measurements on 
 long periods of attention show that there may be waves 
 as long as an hour ; smaller waves, reckoned in minutes, 
 may be traced inside of these ; and within the ' 'minute- 
 waves" we find the so-called ''second-waves." Our con- 
 ception of the flow of attention, or the fluctuation in the 
 capacity for a certain conscious activity, is then this: 
 There are inflnitely short ripplets of attention, hardly 
 perceptible ; these form the surface of ripples, which in 
 turn form the surface of wavelets ; and these wavelets in 
 turn form the surface of waves, and so on. Thus, all 
 attention is rhythmic, and there is rhythm within 
 rhythm from the infinitesimally short to the very long, 
 even daily and annual periodicities. 
 
 The length of the attention-wave (second-wave) 
 varies with numerous conditions, such as kind and 
 strength of stimulus, practice, temperament, psycho- 
 physical condition, effort, etc. The shortest fluctua- 
 tions are probably too rapid to be detected, and ordi- 
 narily a single crest of attention cannot be maintained 
 for more than ten or twelve seconds. For conditions 
 
 * It is evident that the ratio of the length of the crests to the 
 length of the troughs in the above experiment depended upon 
 the strength of the stimulus adopted. When a stimulus is com- 
 paratively weak the troughs are long and the crests short; 
 whereas the order is reversed when the stimulus is comparatively 
 strong. 
 
162 ATTENTION 
 
 like those of the present experiment an average of from 
 six to eight seconds for a complete wave is about normal. 
 The periodicity has come into existence because it is 
 effective, economic, and agreeable.* To illustrate these 
 three features, let us aid our constructive imagination 
 by Fig. 28. The vertical bar represents something that 
 we can be conscious of, e.g., a tone which is not heard 
 because not attended to, and that, as we turn to listen 
 to it, our attention may flow in any one of the forms 
 ttj h, or c, which represent surfaces of equal magnitude. 
 Now if it takes the form a, the object will be in con- 
 
 FiG. 28. 
 sciousness continuously, but only in small part; if it 
 takes the form c, the object will be comprehended com- 
 pletely as it passes through consciousness ; h represents 
 a mean between these two extremes. As nothing would 
 be gained by holding the tone in consciousness longer 
 than c does, c is the most effective form. 
 
 Then, c gives consciousness a period of rest propor- 
 tional in length to the degTee of concentration. As c 
 accomplishes four times as effective work as a with a 
 given quantity of energy and still allows a good period 
 of complete rest before the next wave, it follows that c 
 represents the most economic form of expenditure. 
 
 * The old philosophers had a sort of poetic dream that all 
 nature is rhythmical; and the more we discover of nature's 
 ways the more we see of periodicity. Electricity furnishes a 
 good example: the alternating current is far more effective and 
 economic than the direct. 
 
ATTENTION 163 
 
 When, as in this case, the object of consciousness is 
 constant, when it can be divided into natural groups by 
 attention itself, or when the object is itself periodic, 
 as in music, poetry, or rhythmic movements, the atten- 
 tion-waves adapt themselves to the rhythm so that the 
 essentials of the group are grasped during the crest of 
 the attention-wave and each momentary effort is well 
 timed and is followed by a period of rest. Applying 
 this, then, to the three wave-forms in the figure, we see 
 that as c affords the greatest feeling of ease and com- 
 pleteness in the grasp, permits rest, and tends to make 
 the process automatic, it is the most agreeable.* 
 
 The psychological explanation for our enjoyment of 
 rhythm in all sorts of mental activity is to be found 
 largely in this basal fact of a natural, biological rhythm 
 of attention. 
 
 What are the immediate psychophysical causes and 
 conditions of these wave-forms ? Numerous investi- 
 gators are at work on that problem at the present time, 
 but it is too early to draw any general conclusion, and 
 details would take us too far into technicalities. It is 
 probable that we shall be able to trace the waves into 
 their constituent elements, both central and peripheral. 
 
 Language forces us to use terms which might signify 
 
 the adoption of one or another of the extreme theories 
 
 of attention. This should not mislead us into thinking 
 
 that we know what the ultimate nature of consciousness 
 
 or attention is. 
 
 * There is an analogy in the learning of a game. The beginner 
 is conscious of every step in the process and usually fails; 
 whereas the expert times his effort and uses it only at crucial 
 points. The secret of the Japanese wrestling feat jiu-jitsu lies 
 in the instantaneity of the act. 
 
164 ATTENTION 
 
 2. Division of Attention. — Time O for thirty seconds 
 and let him count aloud as fast as he can from one np 
 and at the same time write numbers in an independent 
 series as fast as he can from one np ; thus, 1, 2, 
 3, etc. Kote errors made in the counting. Let O 
 record the number reached in counting and writing 
 respectively, the errors noted in counting and in writ- 
 ing, and any influence of one series upon the other that 
 he can remember or observe. Make five trials. 
 
 The observer failed in the effort to divide attention 
 and direct it upon both processes at the same time. He 
 noticed an irresistible tendency to allow the attention to 
 oscillate from one process to the other. In so far as 
 the two processes actually went on simultaneously, one 
 was automatic, i.e., went on without attention. Among 
 the conspicuous errors are probably speaking a number 
 due in writing, writing a number due in speaking, and 
 partial combination of a number in one series with a 
 number in the other. 
 
 Strictly we can attend to only one process at a time. 
 When two or more mental processes are supposed to be 
 carried on simultaneously, either the attention oscillates 
 so rapidly from one to the other that they seem simul- 
 taneous, or all but one of the processes are automatic. 
 Usually these two principles cooperate.* 
 
 * James quotes Paullian: "I multiply 421,312,212 by 2; the 
 operation takes six seconds; the recitation of four verses also 
 takes six seconds. But the two operations done at once take 
 only six seconds, so that there is no loss of time from combining 
 them." Here the reciting must have been entirely automatic and 
 habitual in connection with the multiplying. We should not 
 think that the reciting required more attention than ordinary, 
 unchecked, happy whistling would. 
 
ATTENTION 165 
 
 Still we must remember that attention is a matter of 
 degree of concentration. I may see the whole land- 
 scape before me, but see nothing in particular. The 
 process upon which attention is actually directed is in 
 the focus of consciousness, while the other processes 
 must be more or less out of focus, if consciousness is 
 focused at all. All that we do skillfully and nearly all 
 that we do well is done without much attention. 
 Several such processes can go on simultaneously to ad- 
 vantage because they are more or less automatic and 
 demand attention only at crucial points which attention 
 can reach in its oscillations. In the development of 
 habit such points are reduced to a minimum.^ 
 
 3. The Scope of Attention. — Lay a sheet of paper 
 on the table and tap at a uniform rate with the point of 
 a pencil as rapidly as you can on the sheet. Make from 
 three to twelve taps, and require O to say, without 
 counting them, how many taps he heard. Record O's 
 estimate and the true number as shown by the num- 
 ber of dots on the paper. Make ten trials. Before 
 showing the results to O record his statement of how 
 many taps he feels sure that he can estimate correctly 
 within a single span of attention like this. 
 
 The above test, though crude, serves to illustrate the 
 principle that the range, scope, or span of attention is 
 limited. The observer's estimate was probably correct 
 
 * In transcribing rough notes into a finished paragraph on 
 the typewriter, reading, thinking, and fingering are three proc- 
 esses which run parallel, thereby favoring oscillation of attention 
 where necessary. Yet the best work is done when the writer is 
 oblivious of notes or fingering and is completely absorbed in the 
 flow of the thought. 
 
166 ATTENTION 
 
 up to about five taps, but when a group had more than 
 that number of taps the estimate was more or less of a 
 guess on the ''mass." 
 
 The experiment is usually performed as a sight test 
 with elaborate apparatus. Letters, numerals, dots, 
 lines, etc., are shown in groups in exposures which are 
 so short as to prevent eye-movement. In a 0.05-second 
 exposure one can normally grasp with certainty from 
 three to six similar and simple objects, such as letters. 
 If the objects are psychologically more complex, fewer 
 are grasped. If the simple objects are united into larger 
 units, e.g., the letters are united into short words, one 
 can grasp almost as many of the larger units, provided 
 they are familiar; one can grasp about three times as 
 many letters when they form words as when they do not 
 form words. It is about as easy to grasp one's full 
 name as to grasp the initials. In short, the span de- 
 pends upon the coherence of the elements which are 
 grasped together. ^ 
 
 Interest and practice are the main sources of strong 
 grasp of attention. The artist perceives the color 
 
 * The capacity for grasping facts by large units increases with 
 mental development. Take the case of writing: the child first 
 begins on the penmanship stage and is conscious of "position" 
 and parts of letters; he then passes to the spelling stage and is 
 conscious of letters as the elements of words; later he enters 
 the grammar stage and is conscious of words in the construction 
 of the sentence; this leads to the rhetoric stage, in which he is 
 conscious of the construction of the paragraph from phrases, 
 clauses, and sentences; and finallj^, if he really becomes an 
 effective writer, ho reaches the logical stage and the writing is 
 grasped in terms of ideas which take the form of paragraphs. 
 As he reaches each higher stage, the units of the lower stage must 
 more or less "take care of themselves". Few adults reach the 
 highest level. 
 
ATTENTION 167 
 
 scheme of a painting at a glance ; and many a woman 
 sees intricate details in a rival's toilette in but a 
 moment's observation. 
 
 4. Intensifying Effect of Attention. — Suspend two 
 watches, one to the right and the other to the left of the 
 head, at such distances that each can be just distinctly 
 heard. With eyes closed, direct your attention alter- 
 nately to one and the other and observe whether the 
 tick seems louder in the one to which you attend. 
 
 The sensation to which the attention is directed 
 probably becomes stronger. If we strike a chord on the 
 piano and hold the keys down while the tones ring off, 
 "it is possible, by successive attentions, to construct a 
 melody from the separate tones, while the whole chord 
 sounds on as an accompaniment" (Titchener). Some 
 psychologists think that the same may be illustrated in 
 weak sensations in other senses, e.g., color and touch.* 
 But this intensifying effect is limited to comparatively 
 weak stimuli. Strong tones, colors, and pressures are 
 not intensified by attention. An overtone, but not its 
 fundamental, is intensified by attention. 
 
 In a similar manner attention increases the apparent 
 duration of comparatively short mental processes. 
 
 A further closely related characteristic of the process 
 attended to is that it seems to precede other processes 
 which occur simultaneously with it but are not attended 
 
 * This is the principal element in the explanation of "the feeling 
 of being stared at". Many persons report distinct experiences 
 of feeling that a person somewhere behind is staring at them; 
 they are conscious of prominent tactual sensations in the neck. 
 These sensations are normally always present if attended to; the 
 expectant attention intensifies them. 
 
168 ATTENTION 
 
 to. The usual form of the experiment illustrative 
 of this law is to present simultaneously two 
 stimuli while the observer notes that according to the 
 direction of the attention, he can make the one or the 
 other appear to come first. One can make either the 
 bell-stroke or the click of the metronome arise first, 
 although in a good instrument they really sound at the 
 same instant. 
 
 This explains a celebrated experiment which proves 
 that we cannot attend to auditory and visual stimuli at 
 the same time. The experiment is an imitation of the 
 recording of the transit of a star by an astronomer. A 
 sound and a visual impression occur together, but the 
 observer invariably records one as having occurred be- 
 fore the other. What the order shall be is determined 
 by the type of imagery the observer represents.* 
 
 5. Clearness and Detail. — Look at Fig. 29 and 
 answer the question. Observe the apparent changes 
 in the lines of the figure the moment you solve the 
 puzzle. 
 
 Attention makes the image of an object clearer and 
 more meaningful. This is the most striking and 
 fundamental characteristic of attention. Fig. 29 is 
 usually seen first as a disagreeable face and then as 
 
 * About a hundred years ago two astronomers who compared 
 notes found that there was a large constant difference in their 
 observations on the transit. Investigation revealed the fact that 
 one of them was a visualizer and the other an audile; one at- 
 tended first to the visual impression and the other attended first 
 to the auditory impression. The difference between the observa- 
 tions of the two astronomers was alwaj's the algebraic sum of their 
 errors. This discovery marks the beginning of the study of the 
 so-called "personal equation". 
 
ATTENTION 
 
 169 
 
 something entirely different, agreeable, and clear. The 
 details which are clear and dominant when we apper- 
 ceive one view tend to vanish in the background when 
 we apperceive the other. 
 
 It is, however, important to make a distinction be- 
 tween clearness and intensity. Faint stimuli become 
 
 Fig. 29. 
 
 both more intense and clear, while medium and strong 
 stimuli, as a rule, gain only clearness through attention. 
 
 6. Distraction of Attention: Mind- Wandering. — 
 
 Select fifteen consecutive lines from a paragraph and 
 count how many a's there are in the selection. Count 
 as fast and accurately as possible and apply yourself to 
 the task as exclusively as possible. Immediately after 
 
170 ATTENTION 
 
 the counting, retrace the selection and write out a full, 
 frank, and specific account of the irrelevant impressions, 
 memories, thoughts, feelings, and impulses which came 
 more or less into the focus of attention against your best 
 effort. 
 
 Unwavering attention is a fiction. There are great 
 individual differences in the power of application of at- 
 tention, but no mentally alert student can apply himself 
 so closely even to this simple task but that he will have 
 a long and intricate list of mind-wanderings to report. 
 Indeed, the mind wanders so much for all persons that 
 a scant report in this experiment would be indicative of 
 lack of power of observation rather than a high degree 
 of concentration. Like many other processes, such as 
 after-images, double images, etc., which ordinarily are 
 not desirable, these mind-wanderings are not easy to 
 trace without some practice. 
 
 The great scholar who held the egg in his hand wdiile 
 he boiled his watch, and the other one who dropped his 
 watch down the well in place of a stone when he wished 
 roughly to measure its depth, were really thinking about 
 things vastly more important than eggs and watches. 
 There are two kinds of absent-mindedness : the one 
 which comes from extreme absorption in something else 
 (the philosophical), and the one which comes from 
 inability to apply oneself to anything (the scatter- 
 brain). 
 
 The conditions of distraction, the effect of various 
 types of training, the relative value of different types of 
 attention, the advantages and disadvantages of distrac- 
 tion, such are some of the numerous problems connected 
 
ATTENTION 171 
 
 with this topic which await solutiou in the experimental 
 psychology of education. 
 
 7. Sense Processes in Attention. — Observe by intro- 
 spection, in repeated trials, and record the sensory and 
 motor tendencies which are characteristic of each of the 
 following attitudes of attention : 
 
 (a) The attitude of listening as in Exp. 4. 
 (&) The effort to see clearly the irregularities in 
 the period at the end of this sentence. 
 
 (c) Resting a finger upon the point of a pin or 
 sharp penknife and observing the fluctuation 
 in the sensation of pain from the pricking. 
 
 (d) Thinking the names of the five. largest towns 
 in your State, eyes closed. 
 
 (e) Imagining a baseball flying directly toward 
 your face. 
 
 All attitudes of attention have certain tendencies in 
 common, and each attitude probably has peculiar tend- 
 encies which give characteristic sensory impressions.* 
 
 * Pillsbury in his work on "Attention" sums up his chapter 
 on the motor accompaniments of attention as follows : ( 1 ) The 
 muscles of the sense-organs contract so as to give the greatest 
 efficiency. (2) The voluntary muscles of the limbs and the 
 trunk tend to make contractions which have been useful in sim- 
 ilar situations of previous experience. (3) There is a tendency 
 to contract certain muscles regardless of the nature of the stimu- 
 lus. (4) The processes of respiration and circulation are pro- 
 foundly affected. (5) The bodily processes accompany attention; 
 they do not precede it. 
 
 It is these motor processes that one has sensory impressions of 
 in the state of attention. 
 
CHAPTER XIV 
 NOEMAL ILLUSI0:N^S 
 
 For One. 
 
 The problem is to measure certain normal illusions 
 in visual perception of space. The observer must bear 
 the following principles clearly in mind : 
 
 a. These illusions are normal ; if they do not appear 
 in the record, that is proof of either incompetence or 
 abnormality in space estimation.* 
 
 h. These experiments involve a clear distinction 
 between Avhat loohs right and what is right. We shall 
 here devote attention to the way things look, not what 
 they really are. The observer is asked to make ad- 
 justments so that they look right according to his very 
 best ability, but to make any allowance on the basis of a 
 guess or knowledge of the possible direction and magTii- 
 tude of the illusion is forbidden. The value of these 
 experiments depends upon the power of self-possession 
 in observing this distinction, and its chief training value 
 also lies in this. The assignment of this experiment is 
 an expression of confidence in the ability and integrity 
 of the observer. 
 
 c. The observer must perform all the experiments 
 
 * Barring rare cases of special training in certain types of 
 illusion. 
 
 J7? 
 
Plate I. 
 
on ot space 
 
 r.I: 'I roro r-ac^ ^ '■i -;H'i-ial 1 r:i.ir\iiu! in certtt 
 .1 3TAJ*^I 
 
NORMAL ILLUSIONS 173 
 
 before checking any or verifying the accuracy of his 
 judgment hy any means ivliatever."^ 
 
 d. The book should lie upon the table in a normal 
 position for reading, except when otherwise specified, 
 and the observer should maintain the same position with 
 reference to it throughout the series of experiments. 
 This will prevent sighting. 
 
 1. The Arc Terminal Illusion, a. One Horizontal 
 Distance. — Place three silver dollars or other coinSj-j- 
 edge to edge, in a straight row on the table. Remove 
 the middle coin and place it to the right, in the same 
 line, in such a position that the distance between the 
 adjacent edges of the moved coin and the coin now in 
 the middle shall be equal to the original distance across 
 the three coins. Measure and record the distance be- 
 tween the middle and right-end coins, but do not meas- 
 ure the standard or verify by it. 
 
 h. Tivo Vertical Distances. — Place the three coins 
 edge to edge as before ; push the middle one straight out 
 forward into such a position that the distance from this 
 coin to each of the other coins shall look equal to the 
 original distance across the three coins. Record the 
 two variable distances only. 
 
 In the following experiments geometrical figures are 
 made variable by combining some figure in PL I on the 
 
 * If, by any adventure or slip in self-command, the observer 
 should gain objective knowledge of the validity of his judg- 
 ment or aid in the estimation, this must be recorded, as it is sure 
 to influence the following experiments. 
 
 f In the absence of coins, use three disks cut from paper. 
 
174 NORMAL ILLUSIONS 
 
 tissue-paper with some figure in PL II or PL III. Tear 
 the tissue-paper off at the perforation and use it with 
 the printed face down. As printed numbers or letters 
 in the plate would be disturbing elements, w^e may 
 simply agree upon the following designation of the 
 figures in the plates : 
 
 PL II: A, the feathered figure at the top; B, the second figure 
 from the top; C, the slanting bar with the three dots; D, the 
 forked figure at the bottom. 
 
 PL III : A, the large double figure in the upper left-hand 
 corner; B, the slanting, crossed bar with its dot above; C, the 
 cylinder top; D, the parallel lines; and E, the horizontal line. 
 
 2. The Angle-line Terminal Illusion: Lengthening 
 and Shortening Effects. — Place the tissue-paper over 
 PL II so that the apex of the angle of the figure on the 
 tissue-paper lies over the base-line of Fig. A and points 
 toward the left. Bisect the base-line by placing the 
 apex of the angle so that it looks to be at the middle of 
 the line. Measure and record the left section only. 
 
 3. The Angle-line Terminal Illusion: Shifting Ef- 
 fect. — Bisect the base-line of Pig. A, PL II, as above, 
 but use one of the dots on the tissue-paper instead of 
 the apex of the angle figure to mark the middle point. 
 Measure and record the left section only. 
 
 4. The Secondary- figure Terminal Illusion: Attrac- 
 tion of Regard in Length. — Place the long line of the 
 tissue-paper to the right of Fig. B, PL II, by the side of 
 the book ; * cover one end with a piece of thick paper 
 
 * To measure in the book, mark the distance with some sharp 
 point on the edge of a sheet of paper and then measure that on 
 the millimeter scale. 
 
Plate II. 
 
NORMAL ILLUSIONS 177 
 
 and adjust this paper until the exposed part of the 
 >.issiie-paper line looks equal to the middle line of Fig. 
 B. Measure and record the varied line only. 
 
 5. The Attraction of Regard in Direction. — Place 
 the tissue-paper over Fig. C, PI. II, so that the short 
 line on the tissue-paper coincides with the line of the 
 three dots, then slide the tissue-paper upward and to- 
 ward the left, within the same line marked by the dots, 
 until the upper end of the moved line looks to be where 
 the lower line would strike if continued upward in its 
 present direction as a straight line. Measure and re- 
 cord the distance between the right dot and the right 
 end of the moved line only. 
 
 6. The Oppel Illusion: The Bending Effect, a. 
 Upper Line. — Place one of the two dots on the tissue- 
 paper on the joint of Fig. D, PL II, and turn the tissue- 
 paper so that the other dot shall indicate what direction 
 the lower left line would take if continued upward to 
 the right as a straight line. Sighting is, of course, for- 
 bidden. Measure the distance between the movable dot 
 and the end of the line above it only. 
 
 h. Lower Line. — Make the same kind of a measure- 
 ment for the upper left line. 
 
 7. The Poggendorff Illasion: The Breaking Ef- 
 fect. — Place one of the dots on the tissue-paper over the 
 right vertical line of Fig. Ay PL III ; indicate with this 
 dot the point at which the £hort slanting line at the left 
 would strike if continued is a straight line across the 
 
178 NORMAL ILLUSIONS 
 
 space between the two verticals. Measure and record 
 the distance from the top of the line to the dot only. 
 
 8. The Zollner Illusion: The Leaning Effect. — 
 Place one end of the short line on the tissue-paper end 
 to end with the top of the slanting base-line of Fig. B, 
 PI. Ill, and adjust the upper end of the movable line 
 until it seems to make a straight and continuous line 
 with the base-lin?. Beware of sighting! Measure and 
 record the distance between the upper end of this line 
 and the dot lying over toward the left. 
 
 9. The T-Illusion. — Place the long line on the tissue- 
 paper over Pig. E, PI. Ill, so that it crosses it at right 
 angles at the middle ; place a sheet of thick white paper 
 over the tissue-paper so that its upper edge is close to 
 and parallel with the lower edge of the line of Fig. E ; 
 draw the tissue-paper up or down until the vertical line 
 thus formed above the middle of the horizontal appears 
 to be equal to the horizontal in length. Measure and 
 record the length of the varied line only. 
 
 10. The Illusion of the Vertical. — Proceed in the 
 same manner and with the same means as in Exp. 9, 
 except that you erect the vertical at one end of the line 
 in Fig. E, instead of at its middle. 
 
 11. The Illusion of Interrupted Space, a. Hori- 
 zontal. — Place the bar figure on the tissue-paper over 
 Fig. D, PI. Ill, so that the bars coincide and adjust up 
 and down until the whole figure looks square. Measure 
 and record the vertical dimension only. 
 
A 
 
 Plate III. 
 
NORMAL ILLUSIONS 181 
 
 h. Vertical. — Turn the whole figure through 90° and 
 make sidewise adjustments until the whole figure looks 
 square. Measure the varied dimension only. 
 
 12. The Illusion of Length in the Cylinder, -a. 
 Vertical. — Lay the tissue-paper over Fig. C, PL III, so 
 that the cylinder base on the tissue-paper telescopes with 
 the cylinder top in the book ; adjust up and down until 
 the length of the cylinder appears to be equal to its 
 width. Measure the vertical distance between the top 
 and bottom at the middle. 
 
 h. Horizontal.' — Repeat the same measurement with 
 the cylinder in the horizontal position. 
 
 If the observer has shown fidelity and self-control and 
 has been honest enough in these experiments not to 
 sight or check-measure, he has passed a good test of 
 character and may be recommended for a position of 
 trust. The records also constitute a measure of the 
 power of discrimination in visual perception of space. 
 
 The first lesson one learns in the study of sense-per- 
 ception is that ''the senses deceive". The second lesson 
 is that ''there is system in the deception" ; being warned 
 of the presence of danger, we may become the masters 
 of our senses and avert the deception. Both these les- 
 sons are contained in the above experiments, which are 
 intended to show that there are certain universal 
 motives for illusion and that it is possible to determine 
 their approximate force and thus become able to make 
 due allowance for them. 
 
 Now, let the obser\^r turn back to the figures and 
 records and reproduce the setting for each figure (1) 
 
182^ NOEMAL ILLUSIONS 
 
 according to the record, (2) according to the standard 
 measurement given below, and (3) according to the 
 average record given below. In stating the magnitude 
 of the normal illusions, it will be given with reference 
 to a normal adult male wlio is a reliable observer and 
 is not acquainted with the illusion. The illusion varies 
 with age, sex, knowledge of the illusion, power of con- 
 centration, etc. Thus, one of the laws of illusion is 
 that knowledge of the nature and force of the illusion 
 decreases it, often by as much as one half its force; 
 hence the illusion measurement in the first record 
 should now seem too large. 
 
 The standard distance in Exp. 1 is 114 millimeters 
 for dollars or disks. The average normal observer 
 makes the distance about 100 millimeters in 1 a, which 
 means an illusion of 12 per cent. The error is much 
 greater in 1 & ; normally it amounts to more than 20 per 
 cent. 
 
 This form of the terminal illusion is very common in 
 ordinary perception. The simplest form* of it is where 
 we compare the distance between two more or less round 
 bodies with the diameter of one, as in Fig. 30.* Of 
 course the illusion does not rest upon the comparison. 
 The diameter of the figure is underestimated and the 
 distance between the two figures is overestimated, inde- 
 pendently of the comparison, as may be determined by 
 measuring each in terms of a plain line. We need only 
 
 * Fig. 30. This is a copy of a small section of wall-paper. 
 The aim of the artist has been to produce the effect of the ratio 
 1:1, which is the impression obtained by the average observer, 
 but the distance between the figures is actually 10 per cent 
 smaller than the distance across one figure. 
 
NOKMAL ILLUSIONS 
 
 183 
 
 look intelligently at our wall-papers, carpets, bed-covers, 
 table-linen, and patterns in dress goods to find evidence 
 of this illusion. The commonest effects sought by 
 artists are approximately the ratios 1:1 and 1 :1.6. 
 Find designs which give these effects to the eye when the 
 terminals of the distance are arc-formed, and measure 
 them, and you will find that the artist has made allow- 
 ance for the illusion, usually 8 to 12 per cent. The 
 designer of patterns makes free-hand sketches by eye 
 
 Fig. 30, 
 
 estimate and thus naturally makes the proper allowance 
 for the illusion. Where distances of this kind are made 
 equal they do not look equal. 
 
 In Exp. 2 the true distance is 34 millimeters. The 
 force of the illusion is approximately the same as in 
 Exp. la; that is, the measured section is made about 
 12 per cent too short. This is a double figure, because 
 one section has the lengthening effect and the other has 
 the shortening effect. It combines two complementary 
 
184 NOKMAL ILLUSIONS 
 
 illusions. Each of these might be measured separately 
 in terms of a plain line. The left end has the lengthen- 
 ing effect and the right end has the shortening effect. 
 The figure is also called ''full-fledged" because it has a 
 full set of end lines ; a single line would produce the 
 illusion, though not so forcibly. 
 
 This illusion is very common in objects around us, as 
 in trees, fences, and lawn-patches, as well as in designs 
 and structural effects, in fact in all sorts of objects in 
 which a linear distance is marked off at one or both ends 
 by one or more end lines. 
 
 In Exp. 3 the true distance is again 34 millimeters, 
 but the measured section is usually made from 3 to 6 
 per cent too short. This means that the center of the 
 base-line is shifted to the left by that amount. 
 
 When we bear in mind that it is not necessary that' 
 all the end lines should be present, we can realize how 
 commonly the conditions for the shifting effect are 
 present in nature and art. The twigs on a limb seem 
 farther up than they are. The middle point between 
 two branches, one above the other, is not where it seems 
 to be. The cross-line on the letter A seems lower than 
 it really is. 
 
 In Exp. 4 the true length is 52 millimeters, but the 
 varied line is probably made from 4 to 8 per cent too 
 long. This again is a very common situation in all 
 that we see. Teclmicallj^ we say the perception of a 
 primary stimulus is influenced by secondary stimuli. 
 The visual length of an object, Avhatever it may be, 
 varies with the presence of other objects near its ends. 
 
 The first four experiments deal with the terminal 
 
NORMAL ILLUSIONS 186 
 
 illusion of which the angle-line figure^ generally known 
 as the Miiller-Lyer figure, is the most familiar type. 
 They all illustrate the principle that the appearance of 
 a linear distance is modified by the presence of terminal 
 forms. These forms may be grouped roughly into three 
 classes ; namely, the arc, the angle-line, and the detached 
 or secondary figures. The last named are not terminals 
 in the strict sense, as the line is clear-cut in itself, but 
 psychologically they operate as terminals, for we cannot 
 look at the middle line without having our ' 'regard" at- 
 tracted to the end lines. 
 
 The terminal illusion effects may also be grouped into 
 three classes: the lengthening, the shortening, and the 
 shifting. The lengthening effect is illustrated in Exps. 
 1, 2, and 4, and is the result of outward-pointing arcs, 
 angle-lines, or secondary features. The shortening 
 effect is illustrated in Exps. 1 and 2 (the right half) 
 and is the result of the inward-pointing terminal. The 
 shifting effect is illustrated in Exp. 3 and is due to the 
 fact that the angle-lines point in the same direction. 
 
 The strength of the terminal illusion varies with a 
 vast number of conditions in the object, such as the 
 length of the terminals, the angle of the terminals, the 
 number of terminals, the body of the terminals, the 
 relative size of the figures, the vagueness of the ter- 
 minals, adjacent objects, complexity of the figure, mean- 
 ing of the figure or object, time of exposure, etc. As a 
 rule the illusion is decidedly stronger in natural ob- 
 jects than in geometrical figures. It varies also with 
 subjective conditions, such as power of visualizing, 
 training, concentration of attention, mode of regarding, 
 
186 NOEMAL ILLUSIONS 
 
 knowledge or suspicion of its existence, etc."^ Each and 
 all such variables may be made the object of experi- 
 ment. Indeed certain laws have been w^orked out by 
 measurements upon every factor here named. 
 
 The same illusion obtains for the sense of touch. 
 
 The first four experiments illustrate a certain type 
 of illusion of length ; the next four illustrate illusions of 
 direction. The two groups find a natural transition in 
 that Exp. 4, the last in the former gTOup, and Exp. 5, 
 the first in the present gTOup, are both conspicuous il- 
 lustrations of so-called ''attraction of regard". This 
 term is used in both the physical and the mental sense : 
 the physical eye and the "mind's eye" are both at- 
 tracted. That is a principle w^hich runs through both 
 groups. 
 
 In Exp. 5 the true measurement is 11 millimeters. 
 The observer probably made it about 10 millimeters; 
 that is, the adjustable line was not pushed far enough 
 forw^ard. This deflection of the apparent projection 
 of the lower line w^as caused by the attraction of the 
 upper line. How often do we judge direction of a line 
 without the presence at one side of some other line or 
 object ? 
 
 In Exp. 6 a the dot is placed too high by about 2 
 millimeters ; the true measure is 13 millimeters. In 
 Exp. 6 h the dot is placed too low by about 3 milli- 
 meters; the true measure is 26 millimeters. If the 
 low^er left line were actually drawn straight in extension 
 by a ruler, a close observer would see an apparent bend 
 
 * These illustrations are typical of variables in the other eight 
 iypes of illusion also. 
 
NORMAL- ILLUSIONS 
 
 187 
 
 at the joint. Figures 31 and 32 are rather striking 
 illustrations of the Oppel type of small-angle illusion.* 
 
 In Exp. 7 the dot is placed from 6 to 10 millimeters 
 too low, often more than this. The true measure is 21 
 millimeters. 
 
 In Exp. 8 the measurement usually shows a deflection 
 of 2 millimeters from the straight line. The Zollner 
 effect is illustrated in Eig. 33. 
 
 The figiires in Exps. 6, 7, and 8 may be considered 
 examples of the ''small-angle illusion" ; not that the 
 
 Fig. 31. 
 
 small angle is an essential condition for the illusion, nor 
 that it is an explanation, but because it is the principal 
 
 * Fig. 31. The two horizontal lines are straight and parallel, but 
 they look bent on account of the cumulative effect of the Oppel 
 illusion. 
 
 Fig. 32. The circle and the inscribed square are perfect; but 
 if the square is seen square, the circle looks indented. If the 
 circle is seen as a circle, the sides of the square look curved 
 inward. 
 
 Fig. 33. The Zollner pattern. The columns seem to topple or 
 lean by pairs, although they are parallel. The Poggendorff effect 
 makes the short transversals seem discontinuous or broken. 
 There is also a false perspective; the columns seem to form 
 9,lternate ridges or troughs. 
 
188 
 
 NOKMAL ILLUSIONS 
 
 feature which they have in common. The small angle 
 is overestimated in all these cases. The effects of the 
 
 Fig. 32. 
 
 three cases may be called, respectively, the bending 
 effect, the breaking effect, and the leaning effect. 
 
 These figures represent situations that are not un- 
 common in nature, industry, and art. When a straight 
 
NOKMAL ILLUSIONS 189 
 
 line crosses concentric circles, the Oppel effect is at its 
 best. Whenever a line strikes another at a small angle, 
 this angle looks larger than it really is and this results 
 in an apparent bend, deflection, or break of the line. 
 AVherever a line or a long object is crossed by other 
 lines or objects at a small angle, it suffers a deflection. 
 
 The builders of the Parthenon were well aware of 
 what is now called the Oppel effect, and made correc- 
 tions for it by making lines that should look straight 
 curve just enough to correct for the illusion. 
 
 In Exp. 9 we have an illusion which is exceedingly 
 variable and seems to depend particularly upon the 
 discriminating effort one puts forth. The variable is 
 frequently made from 20 to 30 per cent too short. The 
 standard is 34.5 millimeters. The illusion can reach 
 this alarming force because it is the result of the co- 
 operation of several motives for illusion. Where can 
 one turn without seeing examples of it ? Observe a 
 capital T and then measure the proportions. The com- 
 parison of the height and the arm-reach of a man stand- 
 ing with arms outstretched is a good illustration. 
 
 In Exp. 10 we have the well-known illusion of the 
 vertical. A good observer, who is aware of the illusion, 
 will make the variable line from 5 to 8 per cent too 
 short. The standard is 34.5 millimeters. 
 
 In Exp. 11 there is an illustration of the overestima- 
 tion of filled as compared with empty space. The vari- 
 able dimension is made about right in the vertical posi- 
 tion and from 10 to 15 per cent too short in the hori- 
 zontal. This result is due, in the latter case, to the co- 
 operation of this illusion with the illusion of the ver- 
 
190 NOKMAL ILLUSIONS 
 
 tical, and in the former case, to the opposition of these 
 two approximately equal motives for illusion. 
 
 In Exp. 12 a the vertical length is probably made 
 more than 20 per cent too short. This is due to the co- 
 operation of at least four motives for illusion. When 
 the measurement is made in the horizontal position, 
 Exp. 12 by three of these motives are counteracted by 
 the illusion of the vertical and the illusion is probably 
 reduced nearly one half. 
 
 The length of a barrel, the depth of a teacup, and the 
 height of a tank are overestimated on these principles. 
 If a person is asked to estimate the height of a silk hat 
 in comparison with the diameter of the crown, he will 
 overestimate the height by more than 20 per cent. 
 
 Each experiment represents a very large field for il- 
 lusion. There are normal illusions in all the senses and 
 within each attribute of each sense. Thus, in sight, we 
 have illusions of color, space, movement, duration, and 
 intensity, and each of these covers numerous types. 
 
CHAPTER XV 
 AFFECTIVE^TONE 
 
 For Two. 
 
 1. Color Preferences — Each of the eighteen colors 
 supplied in the book envelope is to be compared with 
 every other for the purpose of securing systematic ex- 
 pressions of preference.* 
 
 In each note-book cross-rule a page into nineteen 
 spaces in the horizontal direction and nineteen in the 
 vertical. Insert vertical and horizontal headings as 
 in the table beloAV, which gives numerical order to the 
 six colors and their respective tints and shades. 
 
 Lay a white paper in such a position on a board or 
 book that it shall be at right angles to O's line of vision, 
 in good light and comfortable position for him. Present 
 two colors at a time, placing them systematically about 
 an inch apart on the white paper, and require O to 
 decide which of the two is more pleasing or less dis- 
 pleasing. The decision should be immediate and 
 intuitive, and free from associations. f The table shows 
 
 * This experiment is based on Titehener, "Experimental Psy- 
 chology, Qualitative," Ch. XXI. 
 
 f Avoid theorizing or catering to what ought to be or what 
 would give the best showing as an expression of culture, etc. 
 Let it be a naive and sincere expression of preference entirely 
 independent of the use of the colors. 
 
 191 
 
192 
 
 AFFECTIVE TONE 
 
 the order in which the comparisons should be made ; thus, 
 1 and 2, 1 and 3, 2 and 3, 2 and 4, 3 and 4, 3 and 5, etc. 
 Let O call the order of colors to be presented, following 
 the order shown in the table, and keep the record of his 
 preferences in the prepared blank, simply inserting the 
 
 
 
 1 
 
 2 
 
 3 
 
 4 
 
 5 
 
 6 
 
 7 
 
 8 
 
 9 
 
 10 
 
 11 
 
 12 
 
 13 
 
 14 
 
 15 
 
 16 
 
 17 
 
 
 
 Rt 
 
 R 
 
 Rs 
 
 OS 
 
 O 
 
 oti 
 
 l^t 
 
 Y 
 
 Ys 
 
 Gs 
 
 G 
 
 Gt 
 
 Bt 
 
 B 
 
 Bs 
 
 Vs 
 
 V 
 
 2 
 
 R 
 
 1 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 3 
 
 Rs 
 
 2 
 
 3 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 4 
 
 OS 
 
 34 
 
 4 
 
 5 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 5 
 
 O 
 
 35 
 
 36 
 
 6 
 
 7 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 6 
 
 Ot 
 
 63 
 
 37 
 
 38 
 
 8 
 
 9 
 
 
 
 
 
 
 
 
 
 
 
 
 
 7 
 
 \t 
 
 64 
 
 65 
 
 39 
 
 40 
 
 10 
 
 11 
 
 
 
 
 
 
 
 
 
 
 
 
 8 
 
 1: 
 
 88 
 
 66 
 
 67 
 
 41 
 
 42 
 
 12 
 
 13 
 
 
 
 
 
 
 
 
 
 
 
 9 
 
 iLS 
 
 89 
 
 90 
 
 68 
 
 69 
 
 43 
 
 44 
 
 14 
 
 15 
 
 
 
 
 
 
 
 
 
 
 10 
 
 Gs 
 
 109 
 
 91 
 
 92 
 
 70 
 
 71 
 
 45 
 
 46 
 
 16 
 
 17 
 
 
 
 
 
 
 
 
 
 11 
 
 G 
 
 110 
 
 111 
 
 93 
 
 94 
 
 72 
 
 73 
 
 47 
 
 48 
 
 18 
 
 19 
 
 
 
 
 
 
 
 
 12 
 
 Gt 
 
 126 
 
 112 
 
 113 
 
 95 
 
 96 
 
 74 
 
 75 
 
 49 
 
 50 
 
 20 
 
 21 
 
 
 
 
 
 
 
 13 
 
 Bt 
 
 127 
 
 128 
 
 114 
 
 115 
 
 97 
 
 98 
 
 76 
 
 77 
 
 51 
 
 52 
 
 22 
 
 23 
 
 
 
 
 
 
 14 
 
 B 
 
 139 
 
 129 
 
 130 
 
 116 
 
 117 
 
 99 
 
 100 
 
 7b 
 
 79 
 
 53 
 
 54 
 
 24 
 
 25 
 
 
 
 
 
 15 
 
 Us 
 
 140 
 
 141 
 
 131 
 
 132 
 
 118 
 
 119 
 
 101 
 
 102 
 
 80 
 
 81 
 
 55 
 
 56 
 
 26 
 
 27 
 
 
 
 
 16 
 
 Vs 
 
 148 
 
 142 
 
 143 
 
 133 
 
 134 
 
 120 
 
 121 
 
 103 
 
 104 
 
 82 
 
 83 
 
 57 
 
 58 
 
 28 
 
 29 
 
 
 
 17 
 
 V 
 
 149 
 
 150 
 
 144 
 
 145 
 
 135 
 
 136 
 
 122 
 
 123 
 
 105 
 
 106 
 
 84 
 
 85 
 
 59 
 
 60 
 
 30 
 
 31 
 
 
 18 
 
 vt 
 
 153 
 
 151 
 
 152 
 
 146 
 
 147 
 
 137 
 
 lae 
 
 124 
 
 125 
 
 107 
 
 108 
 
 86 
 
 87 
 
 61 
 
 62 
 
 32 
 
 33 
 
 number of the color which he prefers in the square 
 which forms the intersection of the spaces that run to 
 the two numbers he called. Foot up the results in the 
 table so as to show the total number of times that each 
 color was preferred. 
 
AFFECTIVE TONE 193 
 
 To express the results graphically, take a sheet of 
 cross-section paper, or cross-rule one like the above table 
 blank ; transfer the headings of the table to the base-line 
 and number the horizontal lines from one to eighteen, 
 counting the base-line zero ; make a dot in each vertical 
 column on the horizontal line which denotes the number 
 of times the respective colors were preferred, and con- 
 nect these dots with one bold line, which will then be 
 the curve of color preference. 
 
 It is customary to speak of agreeableness or disagree- 
 ableness of experiences as their affective tone. Our 
 affective responsiveness is a matter of taste. It is well 
 known that we have our likes and dislikes for colors, 
 and that our tastes may differ radically. 
 
 Here we have worked out a detailed expression of the 
 observer's taste for color under the present conditions. 
 It would vary for the same observer under other condi- 
 tions, and some of the doubtful cases might be changed 
 in another trial, but' that throws no discredit upon the 
 experiment which depicts the observer's type. 
 
 Individual differences are marked. One type pre- 
 fers the pure colors, another the tints, another the 
 shades ; one type prefers the soft, artistic tints and 
 shades as opposed to the bright hues; another type has 
 one or more favorite hues, tints, or shades, etc. The 
 curves give good profiles of each type. 
 
 Such measures can, of course, be used effectively for 
 individual psychology. Science, literature, and art 
 are interested in race comparisons and in knowing the 
 culture history of color preferences from the anthro- 
 pological point of view. The teacher is interested in 
 
194 AFFECTIVE TONE 
 
 knowing the color sclienie of the child's temperament. 
 Most of us pass through important changes in color 
 preferences as we pass from childhood into mature age. 
 And, as a mode of teaching the significance of color 
 values, the method could be used effectively. 
 
 On the other hand, the psychologist takes only a 
 secondary interest in such directly practical uses. The 
 chief value of experimental methods of studying affec- 
 tive life lies in the insight they favor and the aid they 
 give in the study of the unfoldment and explanation of 
 the laws of its behavior. This particular exj^eriment 
 reveals nothing in regard to the reasons for color pref- 
 erences, unless it be that the introspection may give 
 some suggestion. But it is by patient and ingenious 
 employment of methods like this under controlled and 
 variable conditions that we shall evolve the real ex- 
 planation of color preferences. 
 
 We know now, in general, that the affective value of 
 color depends upon the specific physiological action 
 of each color, the purpose the color serves, and habits of 
 association. Our experiment, which shows the actual 
 preferences, then naturallj^ suggests three corresponding 
 lines of research in answer to the question, Why is one 
 color preferred to another ? 
 
 There is a tendency in ?esthetics at the present time 
 to look for physiological explanation of modes of agTce- 
 ableness and disagreeableness. What are the character- 
 istic physiological actions of each color? In attempt- 
 ing to answer that question, the experimenter profitably 
 starts from analogies of known effects upon low^er forms 
 of animal life and plant life. Fruits and flowers grown 
 
AFFECTIVE TONE 195 
 
 in experimental greenhouses each covered by a different 
 color of glass show great differences in growth and de- 
 velopment. The red light acts like a fertilizer on the 
 soil, while blue and violet light check growth and 
 produce a sort of dormant condition in the plants. 
 Finsen's discovery of the curative value of the ultra- 
 violet rays rests upon the principle that these rays kill 
 certain disease-germs in the human tissue. The same 
 rays, however, favor the development of various larvae, 
 tadpoles, etc. Color rays strike the most sensitive form 
 of living tissue, the nervous system, through the eye. 
 Ordinarily we become conscious of these affective dif- 
 ferences in effect only in attitudes, general aware- 
 ness of ill-being or well-being. One color is excit- 
 ing, another is soothing, one is fatiguing, another is 
 restful, etc. Shall the explanation of such a physi- 
 ological action be given in large part in terms of 
 chemistry ? 
 
 The second question would search into the signif- 
 icance of the uses of colors. Take red, for example. 
 Red is the symbol of joyous emotion. It is the symbol 
 of sacred rights, of royal power, of victory, of pledged 
 sincerity, and of love. It is the first color to interest 
 primitive man. Words for red are the first color terms 
 to develop in nearly all primitive communities ; a tribe 
 may have half a dozen synonyms for red before it has 
 any name for blue or green. Children seem to repeat 
 the tendencies of the race. Red is the primitive color 
 for decoration; men and women smear themselves with 
 red ochre and paint their utensils and implements in 
 brilliant reds. Red is the dominating tone of color in 
 
196 AFFECTIVE TONE 
 
 religious rites, at the wedding, and at the conclave. It 
 is conspicuously absent in mourning. Children, if un- 
 influenced, tend to use red more than any other color. 
 In abnormal sensitiveness it is red that jars most. 
 The hysteric is conscious, at times, of nothing but red. 
 Likes and dislikes for it are strong. The red flag is the 
 rallying-point for the anarchist. It is the symbol of 
 excitement in epidemics. In brief, red is the color of 
 ripe fruit, it is the color of the flame, and of blood. 
 
 Aside from the physiological conditions and the uses 
 of colors there is a third type of problems which pertain 
 more specifically to the explanation of the habits of 
 association. To what extent can color preferences be 
 cultivated ? What is the biological explanation for the 
 survival of certain types of color preferences ? What is 
 the reason for the order of development of color 
 preference in the race ? In the child ? The present 
 tendency is toward the so-called artistic colors ; is that a 
 permanent characteristic of developed mental life ? 
 
 Let us notice some instances of the use of the method 
 of this experiment in the study of other affective values. 
 
 The matching of color is an important item in dress, 
 in the finishing and furnishing of a room, in art, and in 
 many industries. The psychologist must lay a founda- 
 tion for canons of color harmony by working out the 
 fundamental laws of affective value of color combina- 
 tions independently of their use. It has never been 
 done thoroughly. The thing to do is to select a suitable 
 series of colors and grays and treat a match of any two 
 of these as the unit of the experiment ; thus, the agree- 
 ableness of a red matched with a green may be compared 
 
AFFECTIVE TONE 197 
 
 with a match of red with a dark orange shade. 
 Each color (or gray) must be matched with every other 
 color, and each match must be compared with every 
 other match. From a well-established curve of such 
 results the laws of color harmony might be stated. But 
 when these laws are to be applied in art and industries, 
 the individual variation, accessory influences, etc., must 
 be taken into account, and the problem grows more 
 complicated. 
 
 The curve Fig. 34 (from Wundt) expresses the 
 results of some experiments by a cruder method, show- 
 
 Dark-btue 
 
 Bright-red 
 
 Red 
 
 Orange 
 
 Ir'/U/tt 
 
 Fig 34 
 
 ing the affective curves of matches with red. Height 
 above the base-line represents degree of agreeableness of 
 the match of red with a given color, whereas depth 
 below shows degree of disagreeableness of a combina- 
 tion. Thus, red makes pleasing combinations with 
 other colors in the order dark blue, green, bright red, 
 dark red, and displeasing combinations with violet and 
 orange. The greatest agreeableness is approximately at 
 the greatest opposition (complementary color), and 
 there is a general depression into disagreeableness on 
 each side of this crest. 
 
198 
 
 AFFECTIVE TONE 
 
 In selecting our stationery, in designing a table-top, 
 in platting our flower-garden — in short, wherever a 
 rectangular surface is designed to be pleasing in propor- 
 tions, we may look to empirical psychological laws for 
 guidance. The relative agreeableness or disagreeable- 
 ness of different proportions of a parallelogram is ex- 
 pressed in Fig. 35 (from Wundt, based on Witmer). A 
 series of white cards of equal height but varying length 
 have been compared by a method allied to the one we 
 have used. The length of cards in proportion to their 
 
 Fig. 35. 
 
 height is laid off on the base-line. Elevation above that 
 line indicates relative agreeableness of such proportions, 
 and depression means corresponding disagreeableness. 
 Thus, the most pleasing ratio centers around 1 :1.6, 
 which is known as the golden section or golden cut.* 
 
 * The golden section for the rectangle is that in which the 
 short side is to the long side as the long side is to the sum of 
 the long and the short sides. This proportion may be applied to 
 various forms such as crosses and complex designs. A study of 
 jewelrj^ stationery, monuments, etc.. reveals a most remarkable 
 adherence to these proportions. The commonest cross is in that 
 proportion; the upper section of the upright is to the lower sec- 
 tion as the lower section is to the whole upright. It has been 
 pointed out that many of the forms of nature are shaped in this 
 proportion. Tables, lapboards, and mountings for apparatus 
 made according to the golden section, in the writer's laboratory, 
 give a pleasing effect. 
 
AFFECTIVE TONE 199 
 
 The square is decidedly disagreeable, but the apparent 
 square * is agreeable, although not so agreeable as the 
 golden section. A parallelogram that is a little longer 
 than the apparent square is disagreeable. 
 
 The method may be used with equally good effect in 
 hearing. Music depends upon the agreeableness of 
 certain tone-intervals. Different nations have different 
 scales, and there is a process of gradual evolution of 
 musical scales. Some of the intervals are ''natural", 
 other intervals are more or less arbitrary. There is an 
 instrument called a tone-variator with which we can 
 produce any desired interval. Suppose that we divide 
 one octave into one hundred equal steps and ahvays use 
 the fundamental as one of the two tones. By compar- 
 ing each of "the hundred intervals in such a series wdth 
 every interval in the series, we may establish a curve of 
 the relative agTceableness of these intervals. Such a 
 curve will contain a large number of waves of different 
 amplitude, the crests indicating consonant tones and the 
 troughs dissonant. What light would such a curve 
 throw upon our conventional musical scale ? It would, 
 of course, reveal the natural intervals and show the 
 order of their preference, and then it would show other 
 desirable intervals in the order that they are agreeable. 
 It w^ould show how arbitrary certain parts of our scale 
 are. 
 
 These stimuli are not of any rousing emotional tone. 
 If we should take smell and taste stimuli, we should 
 realize more fully the fact that we are dealing with 
 emotional factors. 
 
 * Due to the illusion of the vertical. 
 
200 AFFECTIVE TONE 
 
 At this point we must impress the warning that there 
 is danger of making these measurements seem too 
 simple and too immediately serviceable. Emotional 
 life is more individualized than cognitive life. We can- 
 not set up the curve of one individual as the norm for 
 aV others, nor can we take the average of a large number 
 of curves and exj^ect one individual to fit that. The 
 conclusions must also be rigorously limited to the condi- 
 tions under which they are taken. Thus, the agreeable- 
 ness of a tone-interval depends upon its sequence, the 
 harmony of the colors depends upon the background, the 
 agreeableness of taste depends upon its relation to other 
 tastes, etc. 
 
 But these are matters which may in turn be made 
 the object of study. It is possible to determine sta- 
 tistically the degree of variability among individuals 
 in affective responses. Instead of covering them 
 over, measurement reveals individual differences. Be- 
 fore a curve is used we must know its coefficient of 
 variability. 
 
 There are two general types of method that may be 
 employed in studying feeling : the method of impression 
 and the method of expression. The above is a method 
 of impression. That is, the experiment simply favors 
 accurate formation and recording of impressions. Im- 
 pression methods may, of course, be used in a great 
 variety of ways. In the expression methods some ob- 
 jective bodily expression of feeling is measured. 
 Among these are' effects upon the bodily strength, in- 
 voluntary movements, volume of certain parts of the 
 body, circulation, breathing, secretions, etc. Exp. 2 
 
AFFECTIVE TONE 201 
 
 will illustrate, in a crude way, the characteristic expres- 
 sions in involuntary movements. 
 
 2. Affective Expressions in Involuntary Move- 
 ments. — The object of the experiment is to determine 
 what direction the involuntary movements of the 
 balanced hand shall take in smelling an agreeable or a 
 disagreeable odor. 
 
 Invite some one who knows nothing about this kind 
 of experiments to act as observer, as the response is 
 influenced by a knowledge of the condition of the ex- 
 periment."^ 
 
 Select some substances that have decidedly agreeable 
 or disagreeable odor such as perfumes, flowers, ammonia, 
 and vinegar. t Keep these in an adjoining room. 
 
 Blindfold the observer and ask him to stand erect and 
 firm and hold his hand about a foot in front of his face. 
 Direct him to say whether an odor is agreeable or dis- 
 agreeable to him when he smells it. 
 
 'Now let one of the experimenters hold one of the 
 odoriferous substances under the observer's nostrils 
 three seconds, so that he gets a good whiff of the odor. 
 Let the other experimenter take an advantageous posi- 
 tion for observation of the movements of the hand and 
 
 * When everything is ready, it should not take more than 
 five minutes to perform the experiment. Proceed with the alert- 
 ness of a photographer and take the invited observer unawares. 
 Tell him that you wish to test his feelings of agreeableness and 
 disagreeableness for odors, and give no intimation by word or 
 sign about your interest in his movements. You must keep his 
 attention away from his hand. 
 
 t One of each kind will do if decided, but it is very advan- 
 tageous to have a good assortment. Care must be taken that 
 the agreeable odor is not too strong. 
 
202 AFFECTIVE TONE 
 
 trace on paper the approximate direction and magnitude 
 of the movement which is made the moment the ob- 
 server perceives the odor. Kecord with this the odor 
 nsed and the observer's statement abont it. Make 
 about five trials with agreeable and -Q-ve with disagree- 
 able odors. 
 
 Agreeable odors have a tendency to cause the hand 
 to reach out away from the body, while disagreeable 
 odors have a tendency to cause a flexion of the arm mov- 
 ing the hand toward the body. 
 
 These movements are unconscious rudimentary re- 
 actions which do not serve any purpose. They are re- 
 flexes which repeat in miniature the general tendencies 
 of action which have as a rule been beneficial. The 
 principle might be stated more freely as follows : When 
 the stimulus is felt as agreeable the hand makes the 
 inceptive movement to get more of it; while, if the 
 stimulus is felt as disagreeable, the hand makes the in- 
 ceptive fending movement for the purpose of getting 
 it away. This tendency shows itself not only in the 
 hand but in the whole attitude. One is the attitude of 
 attraction; the other is the attitude of aversion or re- 
 jection. The direction of the movement may be changed 
 by a slight change in the mode of stimulation. 
 
 To make this test accurately, one should use an auto- 
 matograph, which may be made very simply. It con- 
 sists of a small board suspended from the ceiling as a 
 suitable free support for the hand. A small weighted 
 pencil is placed inside a tube through the board so that 
 it traces the movements of the board upon a sheet of 
 paper laid upon a pane of glass. This is exactly the 
 
AFFECTIVE TONE 203 
 
 same principle as that used in so-called spirit-writing 
 by Planchette or Ouijaboard. These latter instruments 
 convey messages which may be entirely unconscious and 
 involuntary on the part of the writer and still possess 
 coherence and relevancy. The odor experiment above 
 is just as truly spirit-writing as these messages, only 
 it is very much simpler than the mediumistic per- 
 formances. 
 
 The expression of affective tone in strength tests may 
 be demonstrated very simply. The person experi- 
 mented upon is required to pull against a spring which 
 has a mechanism for graphic tracing of the force of the 
 pull. He is required to pull as hard as he can for 
 fifteen seconds ; five seconds after he has started to pull, 
 he is given a whiff of odor (or stimulus through any 
 other sense) and, if the odor is agreeable, the tracing- 
 point will rise, showing an increase in the strength of 
 pull, whereas, if the odor is disagreeable, the tracing- 
 point will fall, indicating a certain amount of falling 
 off in the strength of pull. 
 
 We are stronger when we are under the influence of 
 agreeable stimuli than when under disagreeable stimuli. 
 The modern manufacturer takes advantage of this 
 principle. He gives his workmen encouragement and 
 agreeable surroundings, and finds that they are stronger 
 for it. 
 
 We can tell by the attitude and expression of the face 
 of a man whether he is happy or sad, proud or humble, 
 courageous or cowardly, etc. These differences may be 
 stated in terms of muscular tension, circulation, breath- 
 ings relative changes in the volume of the periphery and 
 
204 AFFECTIVE TONE 
 
 the brain, etc. But very little work of permanent value 
 has been done in this field of investigation. 
 
 There are several reasons for the present dearth of 
 experimental studies in feeling. The processes are 
 extremely elusive : when we turn in upon our anger to 
 study it, the anger disappears. The feelings are not 
 correlated directly with traceable objective conditions 
 as sensations are. The feelings are so diffused and com- 
 plex that it is difficult to obtain and control simple con- 
 ditions. The term feeling is used in more than a score 
 of sanctioned meanings. Theories of feeling are notori- 
 ously numerous. 
 
 The order of experiment must always be from the 
 simple to the complex. It would be interesting to ex- 
 periment on love, hatred, fright, ecstasy, etc., but hardly 
 convenient, or discreet at the present stage. Yet we 
 may answer many of the fundamental questions of com- 
 plex and strong emotion by systematic study of the 
 simpler forms. 
 
CHAPTER XYI 
 KEACTIOIsr-TIME 
 
 For the Whole Class* 
 ^^QuiCK as thought" is often taken to mean infinitely 
 short time, or no time at all. Yet thinking is a distress- 
 ingly slow process with some of ns. A century and a 
 half ago a distinguished physiologist estimated that the 
 speed of the nerve-impulse was about 57,600,000,000 
 feet per second ; a century later it was measured and 
 found to be, in round numbers, 100 feet per second. It 
 was for some time thought to have a speed comparable 
 with the speed of the electric current, but the electric 
 current would flash half the distance around the globe 
 at the equator while a nerve-impulse passes from foot to 
 head in man. The conceptions of the time of mental 
 
 * If the class is large, it may be divided into sections of 
 about twelve to fifteen. Select a conductor, a timer, and a re- 
 corder for each section a week in advance, and let them train 
 themselves so that they are prepared to conduct the experiment 
 efficiently and economically. The conductor shall have general 
 command; the timer shall take the time with a stop-watch; the 
 recorder shall take full notes. The conductor and the recorder 
 cannot be in the chain. If no stop-watch is available, the timer 
 must also be out of the chain so that he can time by counting 
 the ticks of a watch, usually fifths of a second. He can then 
 count by groups of ten-fifths, but may adapt the method of 
 counting to the length of the chain. 
 
 The experiment may be performed in one hour if proper prep- 
 arations have been made and the reading of the explanatory 
 parts is postponed until the experiments have been completed. 
 
 205 
 
206 REACTION-TIME 
 
 processes have undergone equally great revision within 
 the same period. We now measure the duration of 
 mental processes, and these measurements give the 
 mental processes concreteness and a natural setting. 
 They not only furnish the time of the mental act, but also 
 serve to isolate the selected process and make it tangible 
 for the purpose of psychological analysis and synthesis. 
 
 The term reaction-time is used to denote these 
 measurements because it is customary to arrange the 
 experiment so that the termination of the act is marked 
 by a reaction."^ 
 
 To enable the whole class to participate, and to avoid 
 the use of elaborate apparatus, we shall adopt the chain- 
 reaction method. The class forms a chain and a given 
 signal is passed as rapidly as possible from one to the 
 next until it has completed the round. The total time 
 for the chain is divided by the number of participants, 
 which apportions the average individual time required 
 
 * *'A great variety of actions may be viewed as responses to 
 stimuli. There is a flash of light, and we wink; a burning cinder 
 falls upon the hand, and we draw it away; a bell rings, and the 
 engineer starts his train, or the servant opens the door, or we 
 go down to dinner; the clock strikes, and we stop work, or go to 
 keep an appointment. Again, in such an occupation as copying, 
 every letter or word seen acts as a stimulus, to which the written 
 letter or word is the response; in piano-playing, and the guidance 
 of complicated machinery, we see more elaborate instances of 
 similar processes. The printer distributing "pi", the post- 
 office clerk sorting the mails, are illustrations of quick forms 
 of reaction, in which the different letters of the alphabet or the 
 different addresses of the mail matter act as the stimuli, and 
 the placing them in their appropriate places follows as the re- 
 sponse. In many games, such as tennis or cricket, the various 
 waj's in which the balls are seen to come to the striker are the 
 stimuli, for each variation of which there is a precise and com- 
 plex form of response in the mode of returning the ball." (Jaa- 
 trow, "The Time-relations of Mental Phenomena.") 
 
KEACTION-TIME 207 
 
 for the act. It is essential that all should understand 
 clearly what the act is and what attitude to take. Exp. 
 1 will represent simple reactions; all the following ex- 
 periments represent complex reactions. It is in the 
 latter that we measure the time of mental processes ac- 
 cording to the plan here adopted. 
 
 1. Simple Reaction, a. Visual — The signal shall 
 be the quick downward movement of a pencil, and this 
 signal shall be passed as rapidly as possible from one to 
 another. Let the class form a circle and face away from 
 the center. At the conductor's command ^'Ready!", 
 each one shall raise a pencil into plain view of the per- 
 son to his right ; and, about three seconds after the con- 
 ductor's warning ^'Xow!", the timer shall simultane- 
 ously start the stop-watch and give the signal to the 
 person at his right, who shall in turn give it to the one 
 at his right, and so on, the signal being passed as 
 rapidly as possible until it reaches the timer again; 
 and he, instead of passing it on, shall stop the stop- 
 watch. 
 
 In this and each of the following experiments make 
 five successive trials ; compute the average of the five 
 trials and divide by the number of participants. 
 
 h. Auditory. — The signal shall be the exclamation 
 "Up !". Let all keep their eyes closed. In other 
 respects proceed as in Exp. 1 a. 
 
 c. Tactual. — The signal shall be a tap on the right 
 shoulder. Let each one turn 90° to the right and, at 
 the conductor's command ^'Ready !", place the tip of the 
 index-finger of the right hand so that it all but touches 
 
208 KEACTION-TIME 
 
 the right shoulder of the person in front of him. Let 
 all keep their eyes closed. In other respects proceed 
 as in Exp. 1 a. 
 
 The method of measurement here used is crude. The 
 time-measurement is not fine or exact enough; the 
 signal-response is too indefinite ; each participant labors 
 under different conditions; there is little opportunity 
 for introspection; the practice is inadequate and there 
 are many other shortcomings. Yet the experiment 
 serves very well to bring out the experience of time- 
 relations. 
 
 In the laboratory the exact experiments are made with 
 chronoscopes or chronographs which measure small in- 
 tervals of time accurately. A single observer is isolated 
 in an observation-room from which all disturbing stimuli 
 may be excluded. The signal and the response are 
 simplified and made more exact. The observer is 
 trained, numerous trials are made, the variability 
 of the records is computed, the reaction is fraction- 
 ated * for the purpose of the introspection, and the 
 conditions may be controlled and regulated in great 
 detail. 
 
 These "simple reactions" may be reduced to their 
 component parts and, under certain conditions, the time 
 of each of these components may be measured. The 
 complexity of the process becomes apparent wdien we 
 attempt to trace the physical and the mental steps in the 
 act as in the following outline. 
 
 * That is, the observer introspects one aspect of the reaction in 
 one set of experiments and then repeats the experiment and 
 introspects another aspect, etc. 
 
EEACTION-TIME 209 
 
 THE PHYSICAL PROCESS THE MENTAL PROCESS 
 
 1. The response of the sense- 1. The idea of the signal in 
 organ * and the transmission expectant attention. 
 
 of the nerve- impulse to the 
 cortex of the brain. 
 
 2. The progress of this im- 2. The perception of the sig- 
 pulse through the cortex. nal, the association of the sig- 
 nal with the response, and the 
 fiat of the will to respond. 
 
 3. The transmission of the 3. The idea of the movement 
 nerve-impulse to the muscles, followed by sensation of the 
 the response of the muscles, movement. 
 
 and the transmission of sen- 
 sory impulse from the muscles 
 to the cortex. 
 
 The very incompleteness and arbitrariness of this out- 
 line serves to bring out the complexity of the act. These 
 three steps are all complex, both on the physical and the 
 mental sides. The real reaction consists in the second 
 step, in which there is a direct correlation between the 
 mental and the neural process. So far as the mental 
 act is concerned, the first step is merely a preparation 
 and the third step is merely a consequence of the reac- 
 tion. Of the total act, the reaction proper (the second 
 step) occupies but a small portion of the time. There 
 are neural processes in the cortex which correspond to 
 all three steps on the mental side. 
 
 Here, then, we have not measured the time of the 
 mental act of reaction, but the time of a unique set of 
 physical and mental processes in which the conscious 
 
 *The transmission of the sound-waves through the ear and 
 their conversion into a nerve-impulse; the overcoming of the 
 inertia of the retina; or the overcoming of the inertia of the 
 tactual sense-organ. 
 
210 REACTION-TIME 
 
 reaction is the essential element. The simple reaction 
 becomes simpler and shorter, as well as more uniform 
 and irresistible, with practice ; and it tends to be less and 
 less emphatic in consciousness until it becomes practi- 
 tally automatic. All this is implied in and character- 
 istic of the acquisition of skill in any sort of activity. 
 Skill means a quick, uniform, appropriate, and but 
 faintly conscious act. 
 
 Life is a series of reactions. Therefore, in selecting 
 some of these for experimentation, w^e may have great 
 variety in conditions. Among the principal variables 
 in simple reactions are the following: the nature of the 
 impression or signal, the strength of the stimulus, the 
 mode of reaction, the direction of attention, expectation, 
 distraction, degree of concentration, practice, fatigue, 
 individual differences, mental and physical state of 
 health, the influence of stimulants, the influence of 
 mental encouragement or discouragement, etc. 
 
 Take one of these, the direction of attention. We 
 find three characteristic types of simple reaction with 
 reference to this: the sensory, in which attention is 
 directed to the stimulus ; the motor, in which attention is 
 directed to the response ; and the central, in which at- 
 tention is not focused upon either stimulus or response 
 exclusively, but is allowed to oscillate or take a sort of 
 middle ground. The motor is the quickest and most 
 effective form, and there is a tendency to pass from the 
 other types to this with practice. It may become so 
 simple as to be purely a cerebral reflex. 
 
 Or take practice. Practice shortens the reaction-time 
 so rapidly that it becomes a disturbing factor in the 
 
■ REACTION-TIME 211 
 
 present experiments. The gain by practice in Exp. 1 c 
 may so reduce the time in Exp. 2 that the additional 
 factor there involved may not show appreciably in the 
 time. It is customary to distribute the practice evenly 
 among trials which are to be compared. If time had 
 permitted it, that should have been done in the present 
 experiments. 
 
 2. Discrimination. — The signal shall be a tap, as in 
 Exp. 1 c, but it may be given on either shoulder, and the 
 person touched shall respond as soon as he knows wdiich 
 shoulder was touched, but he must determine before- 
 hand which side he shall touch ; i.e., the signal shall not 
 determine what the response shall be, but the response 
 shall not be given until the signal has been distinguished 
 as a right-side or a left-side signal. Let each one hold 
 the tip of a finger close to each shoulder of the person in 
 front of him. In other respects proceed as in Exp. 1 c. 
 
 This act involves the simple reaction to touch plus 
 discrimination ; to get the discrimination-time, subtract 
 the time in Exp. 1 c from the time in this experiment. 
 
 3. Choice. — The signal shall be a tap on either 
 shoulder, as in Exp. 2, but the response must be made on 
 the same side as the signal is received, i.e., the person 
 touched must select one of two possible responses ac- 
 cording to directions after he has received the signal. 
 In other respects proceed as in Exp. 2. 
 
 This act involves the reaction after discrimination, as 
 in Exp. 2, plus the selective choice ; to get the time of 
 the choice, subtract the time in Exp. 2 from this. 
 
 Discrimination and choice are common acts in life. 
 
212 REACTION-TIME 
 
 The exj^eriments might have been varied as to the num- 
 ber of distinctions or choices, the degTee of similarity of 
 the impressions, the specific nature of the impressions, 
 foreknowledge of the conditions, adaptation to the 
 individual, etc. 
 
 Discrimination and choice are clearly mental proc- 
 esses. Exps. 2 and 3 illustrate how we may isolate one 
 process after another for the measurement of its dura- 
 tion, for introspection, and for the building up of a 
 complex mental act of which the elements are known 
 and under control. 
 
 4. Cognition. — The signal shall be a word, and the 
 response shall be another word, predetermined, but 
 spoken only as soon as the signal-word has been 
 ''cognized". Each response becomes the sigiial for the 
 next person. In other respects proceed as in Exp. 1 a. 
 
 This act involves reaction after cognition ; to get the 
 cognition-time, subtract the simple reaction to sound 
 (1 h) from this. 
 
 5. Free Association. — The signal shall be a word, 
 and the response shall be another word — the first word 
 which comes to mind upon hearing the signal. Be sure 
 to call out the first word which can possibly be drawn 
 from the imagery suggested by the signal- word ; do not 
 stop to reason or discriminate.* The response becomes 
 the signal for the next, and so on. In other respects 
 proceed as in Exp. 4. 
 
 * As in the experiments on the laws of association, it is all- 
 important that the response shall be immediate and unreflective. 
 
KEACTION-TIME 213 
 
 This act involves simple reaction, cognition, and free 
 association ; to get the time of the free association, sub- 
 tract the time in Exp. 4 from this. 
 
 6. Restricted Association: Memory. — The signal 
 shall be a word, and the response shall be another word 
 which begins with the final letter of the signal. The 
 response becomes the signal for the next, and so on. In 
 other respects proceed as in Exp. 4. 
 
 This act involves simple reaction, cognition, and a 
 partially restricted association; to get the time of this 
 association, subtract the time in Exp. 4 from this. 
 
 7. Judgment. — The signal shall be the naming of two 
 edibles, and the response shall be the naming of the one 
 of these two which is preferred and one other edible 
 thought of beforehand. The response becomes the 
 signal for the next, and so on. In other respects proceed 
 as in Exp. 4. 
 
 To get the time of judgment proper, measure the 
 time of simple reaction after cognition when the signal 
 and the response each consist of two words, as above, and 
 subtract that time from the above gross time. 
 
 What have we measured in these complex reactions ? 
 We have measured the time of certain purely mental 
 acts of discrimination, choice, cognition, association, 
 memory, and judgment. 
 
 But here a warning and qualification is necessary. 
 Complex mental acts are not made up of simple acts, 
 each butting end to end against one another in time. 
 The total process is ordinarily a fusion in which, how- 
 
214 KEACTION-TIME 
 
 ever, we may trace essential elements or movements. 
 Thus, although the mode of signaling and the mode of 
 response were identical in Exps. 1 and 2, it is not 
 legitimate to assume that the act of discrimination was 
 sandwiched in between these without modifying them, 
 or that the discrimination folloAved step 2 in the simple 
 reaction without modifying that step. The act of dis- 
 crimination gradually fused, on the one hand, with the 
 act of perception of the signal and, on the other hand, 
 with the response. The perception-discrimination- 
 response became one act. 
 
 The process of elimination which we have followed 
 therefore does some violence to fact, and many authori- 
 ties prefer not to use it. For the purpose of most 
 psychological measurements the time of the total com- 
 plex act is quite as serviceable as the time of an isolated 
 portion of the act. But to measure the time of a mental 
 process strictly, it is necessary to use the method of 
 elimination. And it is justified provided we make no 
 superficial assumptions as to rigid demarcations between 
 mental components of an act and adapt the method to 
 the purpose in hand. Even allowing for a reasonable 
 amount of fusion or overlapping, the time-measurement 
 cannot be far from right. In stating a measurement, 
 the fusion is taken for gi^anted. But it is literally indis- 
 putable, e.g., that a given act of discrimination united 
 with a simple reaction lengthens the time by .06 sec. 
 
 Someone may contend that these are all purely 
 physiological processes that we have measured. Para- 
 doxical though it may seem, we may admit the correct- 
 ness of the contention. Modem psychology rests upon 
 
EE ACTION-TIME 215 
 
 the hypothesis that there is a neural process parallel to 
 every mental process. There is great diversity of 
 opinion as to the nature of the connection, but as to the 
 fact of correlation all are agreed. If we are capable of 
 thinking of these processes in terms of neural action, it 
 is certainly correct and legitimate to do so. Instead of 
 speaking of the mental acts of choice, memory, and judg- 
 ment, we are at liberty to speak of these acts in terms of 
 their neural concomitants. But what do we know about 
 those ? Express the fact of judgment in terms of neural 
 action if you can ! Try to get any sort of crude concep- 
 tion of it and you fail. The thing we have experienced, 
 the thing we know most concretely, is the mental act. 
 The fact of a neural concomitant is a good hypothesis, 
 but we have no direct knowledge of the nature of that 
 neural process. We know infinitely more of the mental 
 than of the physical: and the mental is the object of 
 interest and use, the physical being merely a condition ; 
 hence we prefer to speak in terms of the mental. 
 
 All the mental processes here studied are correlated 
 with the neural process mentioned in step 2 of the out- 
 line of simple reaction ; there is only a difference in com- 
 plexity. But cerebral physiology and physiological 
 psychology have very little to tell us in the way of 
 differentiation or description of these central processes. 
 
 There are three factors in the customary numerical 
 records of reaction-measurements which are often of 
 equal if not greater significance than the average time of 
 the act. These are the mean variation, the number 
 and kind of errors, and the ^^mode.'' The mean varia- 
 tion is a measure of the reliability of the measurement 
 
216 KEACTION-TIME 
 
 and the imiformity of the act, and the errors are a 
 measure of the quality of the work done. The mode is 
 that record around which the other records tend to 
 bunch ; it may or may not be the average. If a series of 
 records has more than one mode, that indicates that 
 there is some disturbing factor in the measurement. 
 The four factors taken together may measure changes 
 in capacity for quickness, uniformity, and reliability of 
 action. 
 
 Knowledge of the time of a mental process is in itself 
 of little value. The value of mental chronometry lies 
 in its being a means of comparison. But the time- 
 measurement becomes a sort of scale or foot-rule which 
 may be employed in a great variety of ways. It has 
 probably been used more than any other mode of 
 measurement of its class in psychology. Indeed, in the 
 early period of experimental psychology, persons would 
 ask if experimental psychology had anything but reac- 
 tion-experiments to offer. 
 
 It may be employed to measure certain changes in 
 capacity, such as the effect upon mental capacity of 
 drugs, different types of exercise, rest, practice, fatigue, 
 effort, mental encouragement, health, ideational type, 
 etc. One method of studying fatigue may serve to 
 illustrate this class of applications. The experiment 
 may be so arranged that an individual engages in a chain 
 of reactions. Each response brings out the sig-nal for 
 the next. He must work at maximum speed and with- 
 out interruption for a long period, say one, two, or three 
 hours. The reaction is the work which fatigues, and 
 the continuous graphic record of the whole series of re- 
 
REACTION-TIME 21 V 
 
 action-times contains the measure of capacity for this 
 particular work under various stages of fatigue. The 
 average time in a given minute is the measure of the 
 alertness, the mean variation of the reaction-times dur- 
 ing the same period is a measure of the power of applica- 
 tion, and the record of the number and kind of errors is 
 a measure of the quality of the work done. 
 
 It may be used in the comparison of groups of indi- 
 viduals for statistical, anthropological, educational, com- 
 mercial, and other purposes. It then shows the mini- 
 mum time, the variability, and the quality of any act on 
 which we may make the comparison. Do women 
 ordinarily form quicker judgments than men in a given 
 situation ? In either case, which is the more likely to 
 be right? How does readiness in form-discrimination 
 vary with age, sex, intelligence, race, type of high-school 
 training, etc. ? What element in form is it that gives 
 one sprinter the advantage over another in the start? 
 Which of several candidates has the best natural ability 
 for bank-teller? Such are some of the questions that 
 may be solved by appropriate reaction-measurements. 
 
 It may be used as a measure of discernible differences 
 in any of the senses ; e.g., to determine which one of two 
 or more grays differs most from a given standard gray. 
 It has been of good service in determining the relative 
 legibility of different kinds of printing-type. It may 
 be used as a means of determining individual peculiar- 
 ities in imagery, in working out laws of association and 
 memory, in studying manifestations of the subconscious, 
 etc. The controlled conditions which it demands are 
 most favorable to a close and intimate view of the inter- 
 
218 REACTION-TIME 
 
 relations of elements in a complex act. And it is not 
 without value as a rigid discipline in practical exercises 
 for the development of keenness in perception, memory, 
 reasoning, and action. 
 
 Historically, interest in the reaction-measurement has 
 passed through several phases. It began over a hundred 
 years ago in the study of the personal equation of 
 astronomers. Then the physiologists became interested 
 in the measurement of the speed of the nerve-impulse 
 by this method. This roused the psychologists to the 
 measurement of the time of mental processes. At the 
 present time the interest of the psychologists centers 
 upon its use as an aid in the analysis and synthesis of 
 action. 
 
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