UC-NRLF B 4 305 335 CHAPTERS IN GENERAL PSYCHOLOGY BY STEVENSON SMITH PROFESSOR OF PSYCHOLOGY IN THE UNIVERSITY OF WASHINGTON AND EDWIN GUTHRIE ASSISTANT PROFESSOR OF PSYCHOLOGY IN THE UNIVERSITY OF WASHINGTON Revised Edition 1921 University of Washington Pvess 'Seattle CHAPTERS IN GENERAL PSYCHOLOGY BY STEVENSON SMITH PROFESSOR OF PSYCHOLOGY IN THE UNIVERSITY OF WASHINGTON AND EDWIN GUTHRIE ASSISTANT PROFESSOR OF PSYCHOLOGY IN THE UNIVERSITY OF WASHINGTON Revised Edition 1921 University of "Washington Press Seattle EDUC. PSYCH. LIBRARY CONTENTS I The Elements oe Behavior 5 Behavior dependent on bodily structure 6 Classes of sense organs 8 The exteroceptors 9 The interoceptors 19 The proprioceptors 20 The nervous system 21 Regulatory character of responses 27 Delayed utility of responses 27 Apparent absense of utility of some responses 28 Orientation, locomotion, and intervention 28 Internal responses 30 The action of a stimulus-response mechanism 32 Weber's law 34 The interaction of stimulus response mechanisms 36 Compromise responses 38 II Instinct 39 Classification of instincts according to utilities 40 Individual differences 46 III Learning 49 Positive adaptation 49 Negative adaptation 52 Transitory changes of threshold during a single practice period 55 The conditioned response 57 Facilitating effect of conditioning stimuli 62 Neural basis of the conditioned response 63 The serial response 65 The effects of practice on the serial response 68 Forgetting 72 Whole and part learning 75 Results of the distribution of practice 76 Trial and error 76 The shortening of a trial and error series into a final habit response 79 Imitation 87 IV The Behavior oe Babies 90 V Perception 103 Perception and speech 106 Compromise responses in perception 112 (3) CONTENTS Perceptions from simultaneous stimuli 112 Space perception 113 Visual space perception 114 Visual perception of objects 118 Auditory space perception 119 Auditory perception of objects 120 Olfactory perception 121 Kinaesthetic and static perception 123 Touch perception 124 Time perception 124 Judgment 126 Conviction and belief 130 VI Human Motives 132 The delayed reaction 132 Preparatory and consummatory responses 135 The wish __.„ 137 Attention 137 Volition 138 Drive 141 Sublimation 144 Conflict 146 Overcorrection ' 147 Play 148 VII Social Psychology 152 Fellow man as a constant situation 152 Other prevalent situations 153 Formation of habits in common 155 The spread of tradition 160 Opinion spreads from mouth to mouth 163 Human institutions 164 VIII Consciousness 166 Consciousness and the nervous system 167 Sensation 168 Emotion and affection 171 After-images 171 Association of ideas 173 Imagination 175 Attention 176 Perception 177 The unconscious 177 List of authors- 179 4 CHAPTER 1 THE ELEMENTS OF BEHAVIOR Psychology takes the common sense view that any ani- mal is a physical object in a world of physical objects. It as- sumes that all these objects act upon each other in the ways described by physics, chemistry and physiology. It considers man's behavior as a physical event which can be analyzed into bodily movements. In this sense man's behavior is mechanical and his body is a machine. Any attempt to construct a machine that would respond as elaborately and appropriately as do animals to the world of surrounding objects must certainly fail. This is not because the behavior of animals involves new and mysterious forces lacking elsewhere in nature but because their structure is too complex to be duplicated. It must not be supposed that thinking is denied by physi- ological psychology. A. behavioristic description of man's mind in no way contradicts the common sense assumption that men are conscious. We shall first find out what man does, and under what circumstances he does it, because this is open to observation and may be stated exactly. With this science of behavior as a groundwork, we shall later undertake an account of consciousness. All that we can observe in our fellow man is his behavior. He moves his body and its appendages as he goes from place to place or as he rearranges the objects about him. In con- versation he contracts the necessary muscles and is heard to speak. In emotional expression he blushes, his pulse is altered, his hands grow cold, his liver gives up its sugar, and we see shame, anger, or anxiety. His thoughts, as such, are known to no one but himself. Any physical object is at all times being acted upon by forces which affect it in various ways. The stone lying in 6 ELEMENTS OF BEHAVIOR the road is moved about by the impact of rain, warmed and expanded by the sun, and scratched by the wheels of passing vehicles. Its responses to these forces are simple and easily predicted because of the simplicity of its structure. If we consider not only the stone in the road but also the gopher who sits beside it, we find the same forces acting. The light reflected from surrounding objects falls on both alike, both are struck by the rain or warmed by the sun, but. the result of the action of these forces on the gopher is behav- ior quite different from the behavior of the stone. The light rays reflected from the approaching vehicle cause him to scurry away and those reflected from food cause him to approach. The impact of rain may move him toward the source of impact rather than away from it. Though, like the stone, he is a physical object, he is not merely buffeted about by his environment. Behavior Dependent on Bodiey Structure The difference between the behavior of animals and the behavior of inanimate objects depends upon the fact that animals possess specialized structures. The most important of these structures are the sense organs (receptors), the mus- cles and glands (effectors), and the nervous system. The sense organs are placed in parts of the body where they are exposed to the action of physical forces. Because the various kinds of sense organs differ from each other in structure, some are provoked to action by one kind of physical force and some by another. The physical forces which arouse the sense organs to action are called stimuli. Light has an effect upon the eye which it does not have upon the ear or upon the skin. Gases emanating from a flower act only upon the olfactory sense organs. The stimulus which commonly arouses the sense organ to its characteristic func- tion is called the adequate stimulus. Many sense organs may be stimulated by pressure or an electric current in addition to their more frequently received stimuli. ELEMENTS OF BEHAVIOR 7 The physical forces which stimulate the sense organs differ in kind. Light, sound, heat, impact, gravity, are a few of these and each acts upon some sense organ or another. All stimuli may vary in intensity, and their effect upon sense organs may vary correspondingly. Sense organs are connected with distant muscles and glands by nerve structures. Along these nerve structures pass nervous impulses which result from the stimulation of the sense organs and which, on reaching muscles and glands, may cause muscular contraction or glandular secretion. It follows that any response to a stimulus can occur only when there is a conduction pathway established between the sense organ receiving the stimulus and the muscles concerned in the re- sponse. Such a pathway is called a neural arc. The nervous system contains millions of nerve cells called neurones. These are microscopic in cross-section but are oc- casionally as much as two feet or more in length. Each neu- rone consists of a cell body from which extend branching processes which may lie adjacent to other cells. The points of contact so established offer varying - resistance to the pas- sage of nervous impulses from one cell to another. A con- nection between two neurones which permits the passage of a nervous impulse is called a synapse. The repeated passage of an impulse through a synapse is supposed to increase the con- ductivity of the synapse. Some synapses are present at birth, some occur in the maturation of the nervous system, whereas others are formed in the course of learning. The great number of neurones and the complexity of their connections account for the fact that an impulse leaving a particular sense organ may find its way to one group of muscles at one time and to another group of muscles at another time. The muscles and glands are the effectors or organs of response. They are so situated and so connected by nervous structures that their responses are coordinated and meet 8 ELEMENTS OF BEHAVIOR suitably most situations. They are so connected with sense organs that their action is appropriate to the stimulus. The nervous impulse which is originated by placing something in the baby's hand finds its way to the muscles which cause the fingers of that hand to grip the object. Without such estab- lished pathways of conduction, behavior would be inappro- priate. A significant characteristic of all sense organs is that they are most sensitive to situations which affect the life pro- cesses of the animal. This is accomplished in two ways, first by the position of the sense organs in the body, and second by their structure and by the nature of their adequate stimuli. For example, the eyes are so placed in the front of the body as to receive stimuli from objects which the animal is approach- ing. Placed at the rear they would be less useful. The tongue has a strategic position, as all food must pass its inspection before being swallowed, and the sense organs of taste are affected as are no other parts of the body by chemical stimuli, which are indicative of the food value of any substances taken into the mouth. Classes or Sense Organs Sense organs are divided into three kinds according to their location in the body, the exteroceptors, the interoceptors, and the proprioceptors. 1 Those on the outer surface of the body which respond to external stimuli are called extero- ceptors. These are the sense organs in the skin which respond to touch, temperature, and destructive stimuli, and along with these the sense organs in the eyes, ears, and nose. The eyes, ears, and nose are also called distance receptors because they respond to stimuli whose origin is commonly at a distance, a classification recognized by as early a writer as Aristotle. 2 In addition to the external surface there is the surface of the enteric tract which consists of the mouth, pharynx, oeso- phagus^ stomach and intestines. This surface is also provided 1 Sherrington, The Integrativt lotion of the Nervous System, Lecture 9. 2 Aristotle, de eensu, 43Gb. ELEMENTS OF BEHAVIOR 9 with sense organs and these are called interoceptors. When parts of the external world are taken into the enteric tract as food the interoceptors are stimulated by them and the animal's behavior is adjusted to their presence. The mouse which is outside a cat stimulates the cat's exteroceptors and the cat responds in a conspicuous and characteristic way. Once the mouse is transferred to the cat's enteric tract, the cat's reac- tions are less obvious but none the less important. Movements of rejecting food, of swallowing and of peristalsis, the secre- tion of digestive fluids, and much of the animal's observable behavior result directly from the stimulation of interoceptors. Sense organs occur not only on the outer and the inner surfaces' of the animal but are found also deeply imbedded in the body tissue. These deeply imbedded sense organs are called proprioceptors. Among the contractile muscle fibers are sit- uated receptors which are stimulated by muscle tension. Other receptors in the tendons receive stimuli in a similar way. The walls of bloodvessels are also supplied with sense organs so that circulatory changes affect the animal's behavior. In the head are located the semicircular canals and the organs of static sense, which are stimulated by the movement or by the position of the animal. The proprioceptors are all important in making possible the coordination of bodily movements. 3 The Exteroceptors The most highly developed of the exteroceptors are the distance receptors, namely the organs of vision, hearing, and smell. 4 The Bye. Anyone having an acquaintance with the cam- era will find it easy to understand the mechanism of the eye. Light passes into the eye through a diaphragm called the iris, just inside the anterior wall of the eye, which is called the cornea. Behind the iris is the lens and behind the lens, on the 3 On the classes of sense organs and their functions see Sherrington, Integrative Action of the Nervous System, Lecture 9. 4 For a more detailed account of the structure and function of sense organs and nervous system see Ladd and Woodworth, Elements of Physiological Psychology. 10 ELEMENTS OF BEHAVIOR inner surface of the eye's globe-like wall, is the sensitive retina. The internal cavity of the eye is filled with a transparent mass. That in front of the lens is called the aqueous humor and that behind the lens, the vitreous humor. As we view our own eye in the mirror we see at the center a black spot, the pupil, surrounded by a pigmented ring, the iris. The pupil is a hole in the iris and appears black because it is an opening into the unlighted interior of the eye. It is the color of the iris to which we refer when we speak of brown eyes or blue eyes. Out- side the circle of the iris is the white sclerotic, continuous with the cornea, which with the cornea constitutes the external wall of the eye. (See Figure 1.) Figure 1 — Schematic diagram of a section through the eye. By means of six external muscles the eyeball is moved about in its socket, and in this way a person looks up or down, to the right or the left, converges the two eyes in fixating a near object or so directs them that the axes of vision are ELEMENTS OF BEHAVIOR 11 almost parallel in fixating a distant object. To some extent the eye maybe rotated about the axis of vision. (See Figure 2.) Figure 2 — Diagram of the position of the external muscles which move the eye ball. The iris is a doughnut shaped muscle containing for the most part circular muscle fibres. When these fibres contract, the hole in the center, the pupil, becomes smaller. When the radiating fibres which it contains contract, the pupil becomes larger . For near vision and when stimulated by bright light the pupil becomes smaller. For distant vision and in dim light the pupil becomes larger. The crystalline lens is suspended all around its margin by the suspensory ligament which connects it with another doughnut shaped muscle called the ciliary muscle. When the circular fibres of this muscle contract, the tension on the sus- pensory ligament is decreased and, due to its own elasticity, the lens becomes more convex. In this shape it focuses rays of light from near by objects so that the images of these objects are clearly defined on the retina and the images of distant objects are blurred. When the circular fibres of the ciliary muscle are relaxed and the radial fibres contracted, the sus- pensory ligament is under greater tension so that the lens becomes less convex and the images of distant objects are clearly defined on the retina, the images of nearby objects 12 ELEMENTS OF BEHAVIOR being blurred. When the eyelids are closed and the eye is at rest the circular fibres are relaxed and the lens - takes on this less convex shape, that is, the eye is accommodated for distant vision. Accommodation for near vision, then, involves a smaller hole in both the iris and the ciliary muscle and this is brought about by the contraction of the circular fibres in each. For this reason accommodation for near vision, due to the stimula- tion of sense organs in these muscles, gives us a sensation of muscle strain. In distant vision and dim light, where the circular fibres are relaxed, such sensations are practically absent. The adequate stimuli to the eye are ether vibrations whose frequency is more than 450 billion vibrations per second and less than 790 billion. Lights of different color have different vibration frequencies and intense lights have a greater ampli- tude of vibration than have dim lights. White sunlight con- tains a mixture of rays of all possible vibration frequencies to which the eye is sensitive. Light emanating from a source such as the sun or a candle either enters the eye directly or impinges upon the surfaces of objects, from which it is re- flected into the eye. Light passing through the cornea, the aqueous humor, the lens, and the vitreous humor reaches the retina. In the retina are found chemical substances, which change their composition when acted upon by light, and cell structures, some of which are affected by these chemical changes. Ex- actly what takes place in the retina is not known, but we have reason to believe that the pattern of the image focussed upon the retina sets up various changes in the photo-chemical sub- stances and that these changes affect adjacent cell structures. This is the stimulation which gives rise to nervous impulses. Apart from supporting tissue, the cell structure of the retina is made up of nerve-cell bodies whose long processes, or axones, constitute the optic nerve ; of other nerve cells whose ELEMENTS OF BEHAVIOR 13 function it is to connect adjacent parts and layers of the retina ; and of the rods and cones which may be regarded as the actual sense organs for vision. (See Figure 3.) The rods respond to dim light, whereas the cones respond only to in- tense light. Colored light and white light affect the rods in the same way, no color vision resulting from such stimulation. 5 lOireeTion I J, of li^hT | Geus Bipolar CeUs Figure 3 — Schematic representation of a section through the retina, showing the position of rods and cones, the layer of connecting neurones, and the direc- tion of fibres of the optic nerve. On the other hand the cones give a specialized response to white light and to lights of different colors and it is by means of the cones that we distinguish one color from another. The rods are lacking in the fovea, or that portion of the retina which is directly opposite the pupil. At night when an image of a faint star falls upon the fovea, where there are no rods, it cannot be seen, but it becomes visible when we glance to one side and so cause its image to be displaced toward the periphery, which is so well supplied with these sense organs 5 For the various theories of color vision see Ladd and Woodworth, pages 340ff. 14 ELEMENTS OF BEHAVIOR for dim light. The fovea is richly supplied with cones and is the so-called area of distinct vision. The image of the print which is being read falls upon the fovea and the print could not be read as well if its image were to fall upon the peri- pheral, or outer, margin of the retina. The extreme periphery contains only rods, and for this reason any object casting its image there appears to be without color. When the eye has been exposed to intense light the rods become fatigued and do not function in twilight until after a period of rest. For this reason, if we enter a darkened thea- tre in the daytime we grope blindly for the seat, but if we have come in from the dimly lighted street at night we find our way about without difficulty. In the dark-room it may require a stimulus 8,000 times as great to elicit a response from a light fatigued eye as is required to secure a response from the thoroughly rested eye. This is true, of course, only of parts of the retina where rods are found. The unfatigued eye is sometimes ambiguously called a dark-adapted eye. Ordinarily both eyes are used in vision, and are so directed toward a part of any object which is looked at that the right eye image and the left eye image fall on correspond- ing areas of the two retinae. When this occurs the two images appear as one, and are said to fuse. When the two images fall on non-corresponding parts of the two retinae the object is seen double. In order that the images from a near object may fall on corresponding parts of the two retinae the eyes must be so moved that the lines of vision converge. To secure fusion of the images of a distant object the eyes must be so directed that their axes of vision are almost parallel. (See Figure 4.) An important fact is that vision enables animals to res- pond to objects at a distance. The Bar. The external ear contains a passage leading into the middle ear and separated from it by the tympanic ELEMENTS OE BEHAVIOR 15 Figure 4— Diagram showing the greater convergence required in fixating near objects. The extent of this convergence is a cue to the perception of distance and depth. membrane. When air vibrations impinge upon this mem- brane it oscillates back and forth and causes movement in a series of three small bones situated in the middle ear. The movement of these bones in turn is transmitted to the fluid in the cochlea, which is a part of the inner ear. Thus vibra- tions are set up in this fluid which have the same rate as the air vibrations outside. The endings of a part of the auditory nerve are situated along the base of a row of rods and hair cells which project into the fluid, contained in the cochlea. (See Figures 5 and 6.) It is not certain whether the auditory nerve endings are stimulated by the vibration of this project- ing row or by the vibration of the membrane at the base of the row. The adequate stimuli to the ear are vibrations in the surrounding medium, usually in the atmosphere. These are condensation and rarefaction vibrations and their rate varies from something more than 16 per second to about 50,000 per second. Sound emanates from a vibrating object such as a bell or the vocal cords of an animal and the vibrations are taken up by the atmosphere and conveyed to the tympanic membrane. This enables an animal to respond to objects at a distance. 16 ELEMENTS OF BEHAVIOR oil* ampi Figure 5 — Drawing from a model of the inner ear, showing the cochlea, in which are the sense organs of hearing; the utricle and saccule, the organs of static sense; and the semicircular canals. Figure 6 — Schematic section through one of the coils of the cochlea, showing the basilar membrane and the organ of Corti. The Nose. In the wall of a recess which opens upon the air passages of the nose are found the sense organs for odor. The actual sense organs for odor are long nerve cells embedded ELEMENTS OF BEHAVIOR 17 between epithelial cells and with long processes extending to the surface of the mucous membrane. In the other direction nerve fibres extend from these cells to the brain. (See Figure 7.) Figure 7 — Section throuyh the olfactory membrane showing olfactory cells and supporting cells. The adequate stimuli to the olfactory sense organs are gases and possibly finely divided particles in the atmosphere. These emanate from objects, especially volatile substances, and upon reaching the nose are inhaled past the olfactory area. This makes it possible for the animal to respond to objects at a distance, although the stimulus may be slow in reaching the animal and gives but little indication of the direction of its source. Organs of Touch. There are two kinds of sense organs for touch. On parts of the body where hair is absent, such as the lips and the palm of the hand, are found touch corpus- cles which enclose a core of cells and nerve fibres. On the hairy surfaces the nerve fibres are found coiled about the roots of the hairs. The touch corpuscles (shown in Figure 8) end or nfui-onfc Sensory neuron* Figure 8 — Touch corpuscle from the palm of the human finger, (after Ranvier). 18 ELEMENTS OF BEHAVIOR are plentiful in some areas of the skin such as lips, tongue, and finger tips, and sparsely distributed in other areas. The adequate stimulus for touch is deforming pressure upon the skin adjacent to a corpuscle or to the "windward" of a hair, or pressure upon the hair itself, which stimulates the nerve ending at its roots. Warmth Organs. The warmth sense organs are prob- ably distinct from the cold sense organs. This is borne out by the fact that spots on the skin sensitve to warmth are much fewer than spots sensitive to cold. There are on the average two or three such warmth spots to the square centimeter of skin surface. The organ is probably a cylindrical end bulb found rather deeply imbedded in the skin. The adequate stimulus for warmth is anything which increases within certain limits the temperature of the sense organ. This may be done by the contact of the skin with objects whose temperature is higher than that of the sense organ at the time, by radiant heat emanating from objects at a distance, and by the dilatation of neighboring blood vessels. Dilatation may be produced by the application to the skin of such substances as mustard or pepper. Cold Organs. The sense organs for cold probably have the form of end bulbs, lying nearer the surface of the skin than do the warmth organs. The spots sensitive to cold aver- age between 10 and 15 per square centimeter of skin surface. The adequate stimulus for cold is anything which reduces within certain limits the temperature of the sense organ. This may be done by the contact of the skin with objects whose temperature is lower than that of the sense organ at the time, by skin evaporation, by heat radiation from the skin, and by the constriction of neighboring blood vessels. Certain sub- stances, such as menthol, stimulate the cold organ either by direct action or possibly by causing bloodvessel constriction. A cold spot may be stimulated by a pointed hot rod of a temper- ELEMENTS OF BEHAVIOR 19 ature 45 to 50 degrees C. (The temperature of the blood is 37 degrees C.) This is called the paradoxical cold stimulus. Pain Organs. Certain free nerve endings which are found distributed over most of the body surface are probably sense organs for pain. Pain is also elicited by the stimulation of parts of the body other than the skin surface and possibly results from the intense stimulation of sense organs not pri- marily concerned with pain. The adequate stimuli to the pain organs are mechanical, thermal, and chemical, and must be of much greater intensity than those which are necessary to arouse the organs of touch and temperature. The prolongation of these intense stimuli is usually injurious to the animal. The; Interoceptors Taste Organs. The receptors for taste are situated on the upper surface and the margin of the tongue, a few occuring on the uvula, the epiglottis, and the larynx. They are in the form of end bulbs penetrated by the sensory nerve ending and hav- ing a minute opening on the external surface. They are grouped together in certain of the papillae of the tongue, which are easily observed as small eminences. The adequate stimuli for taste may be divided into four classes : sweet, sour, salt, and bitter substances, and there are probably four corresponding kinds of taste organs. In order to stimulate the organs the substance must be soluble. Many substances such as peppermint, onion, cantaloupe, or cheese are popularly regarded as having characteristic tastes, but these are for the most part odors. When the nose is carefully packed, so that no respired air reaches the olfactory surface, it is impossible to distinguish clam bouillon from beef bouillon, black coffee from quinine solution, honey from molasses, or lemon juice from vinegar. These substances are then responded to as though they were merely salt, bitter, sweet, or sour. 20 ELEMENTS OF BEHAVIOR Other Interoceptors. Sense organs are found throughout the mucous membrane of the alimentary tract. Due to their isolated position less is known concerning their action than is known of the function of sense organs more accessible to ex- perimentation. They are more sparsely distributed than are organs on the skin and, though some respond to pressure and temperature, they are most affected by chemical stimuli. Their adequate stimuli are food substances, internal se- cretions, and the movements of the enteric tract. Thirst re- sults from dryness of the pharynx, and hunger from a vigor- ous peristaltic movement of the empty stomach which occurs at intervals of about one minute. The Proprioceptors Semicircular Canals. These organs, though not auditory in function, are contained in three communicating cavities con- stituting a part of the inner ear. (See Figure 5). The cavi- ties are, roughly speaking, ringlike in form, each one being set at right angles to the other two. Cells with hairlike processes project into the fluid which the cavities contain. When the head is rotated in any plane the contained fluid in at least one of these canals, due to inertia, lags behind the walls of the cavity. Because of this, the projecting hair processes are bent to one side and the adjacent nerve fibres are stimulated. This action may be understood by thinking of a bucket filled with water into which projects moss which is attached to the wooden surface. When the bucket is rotated the water lags behind and the moss is bent. If the bucket is kept twirling for a short time the water takes up its motion and continues to move when the bucket is stopped, thus reversing the direction of the moss. The semicircular canals act in a similar way, so that when a person has been whirled for a time in a revolving chair and suddenly stopped he responds as though he were being turned in the opposite direction. ELEMENTS OF BEHAVIOR 21 The adequate stimulus to these sense organs is rotary- movement of the head. Static Organs. On each side of the head adjacent to the semicircular canals and contained in bony cavities are two small membraneous sacs, the utricle and saccule. (See Fig- ure 5). Within them is a gelatinous mass into which project sensory hair cells. Among the hairs are found small particles of calcium carbonate, called otoliths. The pressure of the otolith weighted mass upon the hair cells varies with the posi- tion and movement of the head. The adequate stimulus to these organs is the position of the hea'd with reference to gravity, or motion of the head in any direction. Muscle and Tendon Sense Organs. (Kinesthetic organs) . In the muscles are found sensory "spindles" made up of modi- fied muscle fibres and free nerve endings. Similar organs are found in the walls of bloodvessels and in the tendons. The adequate stimulus for these organs is the mechanical pressure and state of strain in muscles and tendons which re- sults from any bodily movement. The; Nervous System A stimulus starts a chain of events and a response ter- minates it. Between stimulus and response many things occur in the nervous system. The principle has already been stated that a response can not result from a stimulus unless there is a pathway of nervous conduction between receptor and effector. The whole nervous system is an intricate arrangement of such pathways. The brain is contained in the skull, and the spinal cord is contained in the vertebral column. The brain and spinal cord constitute the central nervous system. Sensory nerves lead from the sense organs to the spinal cord and brain. Motor nerves leave the brain and the spinal cord and lead to skeletal muscles. These sensory and motor nerves constitute the peri- 22 ELEMENTS OF BEHAVIOR pJieral nervous system. In addition to the central and peri- pheral nervous systems there is the autonomic nervous system. This system serves the involuntary muscles and the glands. The muscles which it affects are distinct in kind from the skel- etal or voluntary muscles, being "unstriped" in appearance and slow in their action. Through the autonomic system the cen- tral nervous system is connected with such effectors as sweat glands, salivary glands, tear glands, adrenal glands, liver, spleen, stomach, intestine, rectum, bladder, genitals, heart, and blood vessels. The autonomic has much the same function as the peripheral nervous system. The relation of the three sys- tems may be seen from Figure 9. Autonomic peripheral Figure 9 — Schematic representation of the relations of the autonomic and the peripheral nervous systems to the central nervous system. The Spinal Cord. A cross section of the spinal cord shows an outer white area and an inner gray area whose shape varies at different levels of the cord but preserves a general resemblance to the letter H. (See Figure 10). The outer white area is composed of longitudinal columns of nerve fibres en- cased in their white medullary sheaths. The inner gray area is made up of two posterior and two anterior horns with an ELEMENTS OF BEHAVIOR 23 isthmus of connecting or commisural fibres. Its gray appear- ance is due to the presence of nerve cell bodies lacking the white medullary sheath which gives their color to the outer columns. L l roof AnTfccior Figure 10 — Schematic section of the spinal cord. The dotted area in the center is gray, due to the presence of nerve cell bodies and unmedullated fibres. The outer area is made up of columns of longitudinal fibres. Areas of motor fibres are marked M., and areas of sensory fibres are marked S. Other areas are mainly connecting fibres. The Brain. The cerebral hemispheres constitute the larg- est part of the human brain. The cross section of one of these hemispheres shows an outer layer of gray matter which is called the cerebral cortex. This is made up of un-medullated cell bodies and nerve fibres. A large part of the interior of the brain is seen to be composed of white medullated tracts, al- though there are distributed in this area numerous patches of gray matter. Neural Arcs. A sensory or afferent neurone starts at a sense organ and terminates in the spinal cord. Its branched processes, extending upward and downward, form a part of the sensory columns of the cord, and from these columns its processes enter the ventral horn at various levels. Connecting neurones, sometimes called association or internuncial neu- rones, carry impulses from the sensory systems to motor sys- tems. Every neural arc contains at least one such connecting 24 ELEMENTS OF BEHAVIOR "eurone interposed between its sensnrv « OftndyiTes m spinal cord Figure U-Scheaatic rep r ese„ t a,i„ n „ f sensorv Fkmre 12— ' Ste '" -» anterior horn of the WwT* ^ ^ C ° rtex to th e Cerent w „,o„„ lcad t „ the n c ^ ^^ h °™ motor or ELEMENTS OF BEHAVIOR 25 Figure 13 — Scheme of motor pathways from a sense organ in the skin to a muscle. Arrows indicate possible courses taken by a nervous impulse. The neurones are shown enlarged out of all proportion to the size of the brain and cord. (After Starr.) When an impulse passes from a sense organ to a muscle by way of a sensory neurone, connecting neurones in the spinal cord, and a motor neurone, its pathway is called a reflex arc. 26 ELEMENTS OF BEHAVIOR (See Figure 13). Such reflex arcs are usually instinctive mechanisms. A frog with its brain removed responds to many stimuli by means of these reflex arcs. Regulatory Character of Responses A significant characteristic of responses is that in general they meet successfully the situations which contribute the stimuli that call them forth. For example, a foreign object in the nose calls forth a sneeze response which removes the irri- tating object. The visual stimulus of a fleeing mouse causes the cat to make movements that result in the mouse's capture, just as the mouse, receiving the visual stimulus of a cat, is im- pelled to make movements of flight. A baby will grasp the per- son who holds him if the support is suddenly released. Stumb- ling results in extending the hands, and this protects the more vital parts of the body from injury. A baby cries when he is hungry, cold, frightened, or in pain. This serves to bring his nurse to the spot. We might contrast this mutual regulation in human beings with the be- havior of such a simple animal as the frog. Frogs never come to each other's rescue, even though they have pain and danger calls. The only call which summons the frog's fellow is the mating call. A familiar response of the dog is his scratching reflex. If stimulated with a pin point behind the right shoulder the dog makes rapid oscillatory movements with the right hind leg, the utility of which movement is obvious. If the same stimulation be applied a short distance above the tail at a spot which the scratching foot cannot reach, the tongue makes re- flex licking movements even though the dog does not attack the spot with his mouth. This stimulation of any part of the body brings into play regulatory responses which usually meet the situation appropriately. The stimuli accepted by the distance receptors result in ELEMENTS OF BEHAVIOR 27 responses which adjust the animal to the good or evil which is about to befall it. In their simplest form these responses turn the animal toward or away from the stimulus, or increase or decrease the distance separating object and animal. Decayed Utility or Responses The utility of a response is often not evident until a long time after it is given. The lapse of time occuring between the response and the advantage which the animal reaps from it often makes the response seem a matter of prudent deliber- ation on the part of the animal, when this is really not the case. All responses of lower animals are evoked by present situa- tions, even when the future situations to which they adjust the animal are far distant. This adjustment to the future may in particular cases be fruitless, as the probable event may never transpire, but the response occurs regardless of this un- certainty. These probable events are the situations in the en- vironment of the species which recur periodically, such as night, or high tide, or winter, or new laid eggs. The brooding- hen does not forsee the consequences of her act, but is merely responding to the eggs, the nest, and the physiological changes in her own body. The situation which causes the squirrel to store food in October is not the inevitable scarcity of nuts during the following winter, but rather the surplus food supply in the autumn. Some anticipatory reactions of animals are of use only to others, and an animal often dies before the utility of his act is manifest. A conspicuous example of this is the behavior of the solitary wasp in catching and storing food for an offspring whose birth she does not ordinarily survive. The biological utility of the mating and nest building of birds is the birth and shelter of the offspring. The bird re- sponds, however, to the situation at the time with as little re- gard for the future as man has when he coughs or sneezes in response to foreign objects in the throat and nose. 28 ELEMENTS OF BEHAVIOR Apparent Absence op Utility of Some Responses Although we may usually expect to find some use served by every response, there are many cases of inappropriate re- actions. For example, the instinct which leads a dog to run barking beside the front wheels of an automobile seems to serve no useful purpose either to dog or driver. If we remem- ber, however, that the dog is the descendent of the wolf and that the wolf in killing his prey must depend upon the pack for assistance, it is clear that there was a time when this reaction was of service. By these movements that are so annoying to us in the dog, the single wolf, fleeter than his fellows, over- takes and turns back his prey so that the whole pack take part in the killing. The absence of utility in the dog's case is due only to the fact that he lives in artificial conditions. Many of man's inappropriate responses which are spoken of as immoral have at some period in the history of the race been a necessary means to his survival. Living in a complex civilization makes- many of our orig- inal reaction tendencies inappropriate. Our proneness to anger toward telephone operators, or toward the automobile which resists our efforts to start it, is of no use to us. Our natural equipment does not include appropriate responses to these situ- ations. Loudness of voice and violent action are the innate responses to situations not wholly dissimilar to an irritating operator or to a recalcitrant machine, so these are the re- sponses given by the unregenerate. When a man steps in front of us in the line waiting for theatre tickets our adrenal re- sponse, promoting as it does the clotting of the blood, prepares us for actual bloodshed although this is usually needless as we may never come to blows. Orientation, Locomotion, and Intervention A response to stimulation is often a turning toward or away from certain objects. These objects are usually them- selves the source of the stimulus which causes the turning. ELEMENTS OF BEHAVIOR 29 The altered position generally serves one of two purposes. It may put the animal in a position to employ mouth or legs to advantage, as when a startled animal takes up an attitude of defense or prepares for flight. It may change the direction of the animal's sense organs with reference to the provoking stimulus or with reference to other stimuli usually associated with this. For example the horse cocks his ear toward the un- usual sound, thus bringing the sense organ further into play. The herd wheel in the direction from which danger may be expected in response to the danger cry of the leader. Taking up a posture which permits the appropriate action of receptors or effectors, or which withdraws receptors from stimulation, is called orientation. Many of an animal's movements, such as walking, run- ning, jumping, swimming, crawling or flying, serve to impel him from place to place. Movements which cause a change of location of the animal as a whole are called locomotion. Responses of orientation and locomotion frequently occur simultaneously. If a cow is standing by the roadside facing us as we approach in a vehicle, she merely maintains her orien- tation with respect to the vehicle, by slowly turning her head as we pass. If, on the other hand, we approach her on the flank her head turns toward the road in response to the sound, but she is also actuated to flight. In order to keep her eye on the vehicle and at the same time to move forward, she wheels slowly and crosses the road ahead of us. What seems to be a mere perversity in the cow is explained as a combination of these two action systems. Orientation and locomotion change the position of the animal with reference to objects in the environment, but do not change the position of surrounding objects with reference to each other. Responses which serve to redistribute the parts of the outside world will be called intervention. Movements of orientation, locomotion and intervention all serve to bring new stimuli to bear on the animal and these in 30 ELEMENTS OF BEHAVIOR turn are succeeded by new responses. The proportion of inter- vention responses in higher animals is strikingly greater than in lower forms. In response to variations of season and food supply, birds employ orientation and locomotion, thereby bet- tering their environment. The hermit crab travels about until he finds a shell which affords him shelter. Man, on the other hand, by means of his elaborate intervention responses, so constructs the world about him as to lessen his dependence upon movements of orientation and locomotion, with a resulting in- crease of convenience and safety. He plants his crops and breeds his cattle instead of searching for wild vegetables or game. He is born naked and assumes or discards clothing ac- cording to the weather. He brings together into one place shelter, clothing, bed, food, water, fuel, utensils, mate and off- spring. From his immediate neighborhood he removes dirt, enemies, and dangerous objects. He constructs tools and weapons which are of assistance to him in further movements of intervention. By an elaboration of mechanical contrivances he devises vehicles which take the place of his legs in locomo- tion, and instruments which extend the range and accuracy of his sense organs. Internal Responses The three types of responses just mentioned, orientation, locomotion and intervention consist in movements of the skel- etal muscles. Animals respond also by movements of visceral muscles and by glandular secretion. 6 The dog that smells ap- petizing food not only turns toward the food, approaches and tears it with his teeth, but also responds by certain internal re- actions of peristalsis and secretion. Peristalsis is a wave-like muscular constriction of the enteric tract that serves to carry food, once taken into the mouth, into stomach and intestines, and to knead the food in such a way that all parts of it are brought into contact with the secreting and absorbing walls. C For a detailed account of such internal responses see Cannon, Bodily Changes in Pain, Hunger, Fear, and Rage. ELEMENTS OF BEHAVIOR 31 Secretions into the enteric tract serve to prepare the food for absorbtion. The principal glands that serve digestion are in the mouth, stomach, intestines, pancreas and liver. At the sight or smell of food, the mouth and stomach are prepared by their secretions to receive it. The flow of these secretions is later increased by the presence of food in the mouth, by the movements of chewing, and by the peristalsis of which swal- lowing is a part. When a cat is enraged by a barking dog it not only "spits" and assumes the posture of defense, but its peristalsis ceases, and the bloodvessels so change their size, by the play of minute muscles in the vessel walls, that a greater blood stream reaches the fighting and fleeing groups of skeletal muscles. Sugar stored in the liver is liberated. From the adrenal glands ad- renin is secreted and poured into the blood, with the result that fatigue is counteracted and the vasomotor condition and ab- sence of peristalsis are maintained. Heart beat and respiration show an appropriate increase of amplitude and rate. As a rule internal responses do not occur alone, but accompany move- ments of orientation, locomotion, and intervention. They fa- cilitate these movements and in turn are further excited by them. Emotional expression is made up of overt bodily move- ments and of characteristic internal responses accompanying them. The grouping of responses in each emotion shows great resistance to the rearranging effects of training, as is indicated by their fundamental similarity in diverse races. Grief, merri- ment, anger, and love are expressed in much the same way the world over. They are aroused, however, by varying situa- tions in different societies. 7 When a person is stirred to action by the internal re- sponses of rage, fear or love we say he is "moved." This is more than a mere figure of speech. A situation which hampers movement causes the response of struggling with head, body, 7 See Darwin, The Expression of the Emotions in Man and in Animals, pages 83-115. 32 ELEMENTS OF BEHAVIOR arms, and legs, but it also, either directly or due to the strug- gling, causes certain internal responses like those described in the case of the enraged cat. These internal responses stimu- late proprioceptors in the viscera. The impulses so aroused are conveyed along neural arcs to the muscles engaged in struggling, and their action is thereby strengthened and sus- tained. If the pathways of nervous conduction between these proprioceptors and the skeletal muscles should be severed, this reenforcement would not take place and the struggling move- ments would be less energetic and shorter lived. The secretion into the blood of adrenin from the adrenal glands reduces the peristaltic movements in the intestinal tract, increases by its action upon bloodvessels the amount of blood in the skeletal muscles, and by direct contact makes more ener- getic the contraction of the skeletal muscles involved in the ex- pression of rage. It probably promotes clotting of the blood which is of advantage in case the ensuing fight results in the animal's being wounded. This action of adrenin is another way of eliciting a re- sponse. Between the gland and the muscles acted upon there is no nervous connection. The blood stream carries the gland's secretion to the muscles, and the secretion has a direct chemical action upon the muscle tissue. Thus the direct action of in- ternal secretions from ductless glands is complementary to the conduction of impulses from visceral proprioceptors through neural arcs. The effect of these secretions is less prompt than is the effect of neural reenforcement, but persists for a longer time. The Action of a Stimulus-Response Mechanism Many weak stimuli, which act upon sense organs without causing a response, will be found to call forth a response when the stimuli are increased in intensity. A stimulus of an inten- sity just sufficient to bring about a reaction is called the threshold stimulus or liminal stimulus. We may give a baby a quinine solution so weak that he will swallow it as though it ELEMENTS OF BEHAVIOR 33 were pure water. If the strength of the solution is gradually increased, we reach a point at which the baby will grimace and turn his head away. This constitutes the threshold point. If, instead of increasing in intensity a stimulus which is less intense than the threshold stimulus, we repeat such a stim- ulus again and again, a response may be elicited. Bringing about a response by the repetition of a subliminal stimulus is called the summation of stimuli. If, for example, a neighbor comes at night and knocks on a man's door and the man re- mains in bed, and if the neighbor continues his knocking, the man finally rises from bed and lets him in, not because it is more reasonable to do so now than it was before, but because of the neighbor's importunity. The summation of stimuli is used extensively in advertis- ing, the recurring advertisment often leading us eventually to buy the article described. This accounts in part for the num- ber of people who use Ivory Soap and Bull Durham. The daily sight of the unanswered letter in the letter tray may finally call forth a reply. The ingenious torture which con- sisted in allowing a series of drops of water to fall on the bound victim produced a summation effect resulting in a greatly increased response. Within certain limits the summation effect is increased as the length of the intervals between the subliminal stimuli is diminished. If the intervals are lengthened beyond a certain point no summation effect occurs. A response is sometimes given only after a number of diverse subliminal stimuli have been received, and may be the result not only of the last stimulus but of the entire series. Bringing about a response by a series of diverse subliminal stimuli is called the summation of diverse stimuli. The pros- pective purchaser of an automobile is led to visit the salesroom but remains irresolute in the presence of the machine. The salesman now initiates the process of summation. He calls the man's attention to various good features of the machine, 34 ELEMENTS OF BEHAVIOR and each of these stimuli brings the man nearer to parting with his money. The salesman appeals to his customer's van- ity by reference to prominent men who own that make of machine. Finally a stimulus is given, such as the assurance that after this car is sold none will be available for several months, and the purchaser makes out his check. To induce a child to take medicine, the summation of diverse stimuli is often effective. If a promise of candy or of money does not have results we may try such bribery as offer- ing to take him to the theatre, or we may threaten to leave him at home. Finally, by petting or cajolery, the summation is completed. We often describe a person as being favorably disposed toward a certain course of action. This usually means that he has already received the first few of a series of diverse stimuli and all that we need do is to complete the series in order to bring about the response. For example, a man's child may have died recently and we realize that the time is auspicious for asking him to contribute to a children's charity. The acquaintance whom we would greet casually at home is welcomed effusively in a foreign country because we are already stimulated to friendliness by the internal changes which in part constitute homesickness. The response to a series of stimuli varies according to the order in which the stimuli occur. A man standing beside a dark road responds differently to the sounds of approaching footsteps and to the sounds of retreating footsteps, which may be exactly the same sounds occuring in opposite order. Royce pointed out that it makes a difference whether a stranger first steps on a man's foot and then apologizes, or first apologizes and then steps on a man's foot. Weber's Law Within certain limits the intensity of a stimulus may vary without modifying the nature of the response. If the ELEMENTS OF BEHAVIOR 35 stimulus is increased or decreased beyond these limits, the response alters its character or its energy. The amount by which a stimulus must be increased or decreased in intensity in order to alter the response is called the differential thres- hold. This term should not be confused with liminal threshold. About 1825 it was suggested by Weber, a German inves- tigator, that the ratio of the differential threshold to the amount of the stimulus is constant at all intensities for each class of stimuli 8 . Although the law does not hold for very weak or for very intense stimuli, it has proven a demonstra- ble and valuable generalization. The ratio differs with different kinds of stimulation, being, for example, smaller in the case of light than in that of sound, yl The reflected light from a candle introduced into a sunlit room may not be noticed, but such an increase of illumination in twilight is at once apparent. It may be impossible to dis- tinguish between a pitch of 512 vibrations and one of 513, but easy to hear the difference between pitches of 32 and 33 vibrations. A weight of 80 grams and one of 82 grams may be reported as being the same, but a weight of 20 grams and one of 22 will probably be recognized as different. It is evident that the apparent difference between two lights does not depend so much upon the absolute difference between the stimuli as upon the proportion of this difference to the intensity of the light. An absolute difference between two sound intensities does not insure our distinguishing between the two, for if the intensities are great this difference may be inade- quate. The same is true of two weights. In order that the two may stimulate us to different responses, it is necessary that one shall be about three percent heavier than the other. The just noticeable difference for light is about one percent of the intensity of the stimuli. These differential thresholds vary greatly with different subjects and hold only within a limited range of intensities. 8 For a more detailed account of Weber's Law see Ladd and Woodworth, Elements of Physio- logical Psychology, pages 361ff and 374ff. 36 ELEMENTS OF BEHAVIOR The; Interaction or Stimulus-Response; Mechanisms As no animal is ever acted upon by just one stimulus at a time, but at any given moment is exposed to a great complexity of stimuli, its resulting behavior is the interplay of many re- sponses. The action of any stimulus depends on the other stimuli which occur along with it. A loud sound heard on the city streets causes a response different from that given to the same sound when the hearer is alone in the woods. The combination of all the stimuli to which an animal responds at any moment is called a situation, and a combina- tion of responses is called an act. 9 If the situation which confronts the animal tends to arouse simultaneously two stimulus-response mechanisms there may occur one of two results. One of the mechanisms, though not itself responding, may increase the tendency of the other to respond ; or one may interef ere with the action of the other. The first of these results, where one system is an aid to the other, is called facilitation. This aid or reenforcement produces a more lively response in the system which is facili- tated. Suppose a man, seeing a bear in the woods, responds by a dignified retreat. The bear now moves in the man's direction and he, previously walking, breaks into a run. Pigs eat more greedily when other pigs are sharing the meal, and almost any animal will partake more rapidly of the food which we threaten to remove. A toothache ends our delay in visiting the dentist, and a good appetite makes us respond promptly when summoned to dinner. An increased tendency to act is to be expected when two stimuli lead to the same response, but this increased tendency may also occur in cases where the responses produced by the two stimuli are not the same. The difference between facilitation and the summation of stimuli lies in this, that the stimuli combined in summation are 9 These y Watson, Psychology from the Sian-dpoint of a Bchayiorist, pages 10. 11. ELEMENTS OF BEHAVIOR 37 all subliminal and occur serially, whereas the stimuli combined in facilitation may or may not be subliminal and if subliminal must occur simultaneously. Contrasted with facilitation is the case of interference between two stimulus-response mechanisms. As a result of interference three things may happen; either both responses are given with lessened energy, or one response is given with lessened energy and the other is not given, or neither response occurs. The hampering effect which one system has upon another is called distraction. The preventing effect which one system has upon another is called inhibition. If a trap is baited and an animal is led by the odor of the bait to approach the trap, and if there is no odor of man about the trap, the animal will seize the bait and be caught. If, however, the body odor of the trapper adheres to the trap, the animal will either take the bait less readily or will entirely disregard it. If the bait is taken reluctantly the body odor is a distracting stimulus; and if it is not taken at all, the body odor is an inhibiting stimulus. The reason one response prevails over the other is either that there is more resistance in the conduction path of one system than in that of the other, or that the relative strength of the two stimuli in terms of their thresholds is different. 10 When interference so raises the threshold of both re- sponses that neither is given, we have mutual inhibition. In this case a third stimulus may bring about a response which removes the animal from the first two stimuli, and the inter- ference disappears. This may be seen in the case of a man who is addressed by someone while he is reading. He pauses in his reading and it is now doubtful whether he will answer the questioner or resume his book. One of these responses will eventually be given unless a third stimulus, such as the ringing of the telephone, causes him to disregard both book and questioner. Ordinarily man is acted upon not by two but 10 For a discussion of the neural basis of interference see Sherrington, The Integrative Action of the Nervous Syxtem, pages 55, 115-149, 223. 38 ELEMENTS OF BEHAVIOR by a multiplicity of stimuli, and his rsponses are determined by facilitating stimuli, inhibiting stimuli, distracting stimuli, and by the stimuli which primarily elicit the response. Compromise; Responses When a spinal dog is simultaneously stimulated at a point on the shoulder and at a point several inches farther back, he scratches a spot somewhere between the two. His response is in the nature of a compromise. Man, as well, when stimu- lated to two distinct responses often acts in a way which is a resultant of the two response tendencies. When playing ball with a stone we tend to throw it as if it were a ball to the person who is about to catch it, and we tend to refrain from throwing it because we are in the habit of not stoning our friends. The resultant act consists in throwing the rock gently. Compromise in emotional responses is the rule rather than the exception. If a child's mischief annoys us, we re- spond to him both as to a child to be treated kindly and as to a nuisance to be abated. The resultant response is remonstrance with sad good humor. When a puppy is scolded his behavior is a compromise between affection and fear, and is somewhat suggestive of the politeness of human beings in the presence of strangers. CHAPTER 2 INSTINCT If we know the structure of a machine we can predict what it will do whenever it is acted upon in a familiar way. Man is no exception to the rule, and we find that in so far as men are alike in structure they respond in the same way to any event which affects their sense organs. Babies all show a great similarity of structure at birth before they begin to learn, and to a considerable extent this similarity of structure persists even when they become adults and after each has taken on individual peculiarities due to the particular influences to which he has been exposed. In addition to this partial persis- tence of the baby's original nature, there is a closely related fact which helps to make all men somewhat alike. This is the fact that the structures of all of us tend to change in the same way due to our growing older. This change we call maturation. The behavior which is due to original structure, or due to the changes in original structure which are the results of simple maturation, we call instinct. Only by accepting such a definition as this is it possible to describe all behavior as either instinctive or learned. European psychology is responsible for the uncritical description of instinct as the behavior which is common to all men. Although all men are fundamentally alike in their original structure, there are individual differ- ences in instinctive endowment, and this individuality is no less instinctive than commonality or universally shared traits. Furthermore, a great deal of the behavior which is common to all men is undoubtedly learned. Everybody knows how to use a stick as a weapon, but no one does so instinctively. Wear- ing clothing is as universal as many of the elaborate instincts of lower animals, but is of course a learned act. The behavior which is characteristic of any particular culture, and which (39) 40 INSTINCTS is not found elsewhere, cannot be attributed to original struc- ture, but should be regarded as the effect of environment. Classification of Instincts According to Utilities We may classify instincts according to the situations which call them forth, according to the acts involved, according to the accompanying emotions, or according to the utilities the instincts serve. 1 The first two methods of classification are the most desirable, but are difficult because among different species a given situation results in so great a variety of move- ments and a given response may be elicited by so great a var- iety of situations. A complete catalogue of responses accord- ing to situation, or of situations according to response, must be attempted in the case of man, but this would be too detailed and cumbersome in a preliminary description of the instincts of lower animals. 2 A classification according to the emotions is unsatisfactory because the emotions themselves have not yet been described with sufficient exactness, and because the nature of the emotional accompaniment of many instinctive acts is obscure. The uses which responses serve may conveniently be divided into a few well recognized classes, and this division is most popular in listing the instincts of animals in general. The final or consummatory response in any series of instinctive acts is always the basis of such a classification. Mating behavior is always terminated when copulation occurs. Food-seeking is always terminated by eating. Nest-building ceases when the nest is finished. Flight continues until a place of security is reached. Combat ends when the foe is killed or routed. The body is scratched until the parasite is removed. The behavior which leads up to these consummatory responses varies greatly according to the situation, but the consumma- tory responses themselves are highly predictable. 1 Classifications Of human instincts are to be found in .Tamos, Principle* of Psychology, Chapter 14; Thorndiko, Educational Psychology, Vol. I; MoDougall, Social Psychology, Chapter 3. 2 A description of original human nature in terms of responses according to situation is undertaken by Xhorndike in Vol. I of his Educational Psychology. See also Woodworth, Dynamic Psychology, Chapter 8, "Tho Native Equipment of Man." INSTINCTS 41 The nest building of birds and insects, the web building of spiders, and the cocoon spinning of larvae are striking examples of complicated and elaborate instincts. These acts may be futile if the normal course of events is interfered with, but the lower animals are not deterred by minor irregu- larities of situation. Elaborate and serially combined re- sponses are characteristic of their instinctive behavior. On the other hand, the instinctive acts of man are relatively simple, but in the process of learning, these simple responses take on many and varied combinations. The more we investi- gate man's original nature the less intricate his instinctive reactions appear to be. We ought probably to regard the elaborate instincts attributed to man by the school of William James as being for the most part learned acts. Under each of the following utilities will be listed a number of responses to illustrate the variety of ways in which lower animals adjust themselves to their needs. Probably few of these responses are purely instinctive. Certainly, in the case of man, nearly all these utilities are served by learned acts. Food Suckling, together with head and leg movements. Swallowing. Following while suckling. Mouth gaping by young birds. Crying and whining of young. Licking. Disgust rejection. Nursing the young. Regurgitation by pigeons. Scratching the ground. Inserting food into the mouth of young. Clucking by mother bird. Storing food for larvae. Restlessness due to hunger. Following a scent. Stalking. Chasing. Crouching. Lying in ambush. Springing. vStriking by snakes. Striking of fish. Diving by birds. Stinging and sucking by insects. Grasping. Constriction by snakes. Biting. Pecking. Tongue movements of lizards and frogs. Lapping. Chewing. Grazing. Rumination. Grit Eating by birds. Grass eating by sick dogs. 42 INSTINCTS Creating water currents. Seizure due to contact. Hunting cry of owls and lions. Web building. Carrying home food. Food storing. Migration. Fighting and intimidating pos- sible competitors. Threatening wing movements of pigeons while eating. Hunting in packs. Ants guiding fellows to source of food. Reproduction Preliminary restlessness. Mating calls. Drumming by partridge. Odoriferous secretions. Strutting, showing off, dancing. Coyness of females. Fighting among males. Nuptial flight of some insects Migration. Consummation of courtship. Polygamous and polyandrous grouping, and Affectionate behavior toward permanent mate. Laying eggs. Setting. Care of eggs. Shelter Restlessness in the open. Stereotropisms. Seeking temporary concealment. Retirement to shelter in response to darkness. Symbiosis. Permanent residence in caves, rock shelters, hollow trees. Seeking shelter high above the ground. Orientation toward entrance of habitation. Burrowing and excavating. Cocoon spinning and the use of secretions in building. Caterpillar's use of leaves in building. Collecting building materials such as mud, sticks, leaves, hair. Rearranging these into nests and dens, in trees, on ground, in burrows. Plucking fur and down from breast for lining nest. Dam building by beavers. Yarding of moose. Huddling of cattle. Laying eggs in foreign nest by cuckoo. Cooperative nest building of in- sects. Defense Restlessness when alone and seeking company of fellows, resulting in herds and colon- ies. Secretions of cuttlefish, skunk, etc. Discharge of nematocysts. Taking up posture which makes the animal seem more formi- dable. Snarling, growling, screaming (often in defense of food). Cries which summon aid. Responding to cries for aid. Groaning. Immobility. INSTINCTS 43 Frogs' ceasing to croak on ap- proach of intruder. Flight (often to place inacces- sible to pursuer). Concealment. Withdrawal m o.v e m e n t s of snails, bivalves, turtles, etc. Flexion of porcupine. Defensive grouping of herd. Attack with bill. Fighting with wings. Residual fighting movements of pigeons while eating which serve to threaten opponents. Cry of warning to fellows. Clinging of young. Resisting forcible manipulation. Struggling, squirming, biting when held. Clinging to object when aggres- sor attempts to take it away. Fawning, placating and ingratia- ting behavior. Mother bird's attracting atten- tion from nest. Retaliatory aggression. Leaning away from heights and clinging. Withdrawal from water. Attack directed toward obstacles and confining objects. Flight from odors of natural enemies. Cat's finding new nest for kit- tens that are often disturbed. Cleanliness Licking the bodv. Dusting plumage. Preening. Scratching. Biting parasites. Shaking of wet paw by kittens. Picking off foreign objects from surface of body. Cleaning of eggs by ants. Rolling Shaking Avoiding putrid matter. Scratching dirt over filth. Careful observation of animals will disclose the fact that practically none of the items in the above list refers to an act which is always executed in the same way. An act of flight, for example, is never twice the same. The movements depend upon the contour of the ground, upon the position of the ene- my, and upon previously formed habits of all sorts. Such "instincts" as these are nothing more than the continuance of behavior of many sorts until a consummatory response has been given. A frightened partridge uses many means of escape, struggling, running, or flying, until the consummatory response of reaching concealment terminates its activity. Greater uniformity in the order of the parts of an elabor- ate "instinct" is seen when each component act changes the situation in a set and characteristic way. Nest-building is a 44 INSTINCTS case in point. A shelf under the eaves is a stimulus which may start a mated bird in its search for building materials. Its return to this spot with material in its mouth initiates laying the foundation of the nest. Its empty bill starts it off again on a search for more materials. Return is delayed until its mouth is again filled. Its second nest-building movement is deter- mined by finding the nest already begun, and so each step in the building is governed by the degree of completion of the nest at the time. This may be demonstrated by partially demolishing a nest which has been almost completed. The bird will act then much as it did when the nest first reached this stage of completion. To call pugnacity, or constructiveness, or acquisitiveness, or self-preservation, or mating, an instinct is a dangerous con- cession to popular usage. Each component act as elicited by a particular situation might better be so called, always bearing in mind that this series of acts is terminated by a consummatory response. A complete understanding of behavior always in- volves an analysis in terms of stimulus-response mechanisms, and to name, for example, all the behavior of carnivorous ani- mals which results in securing food "the" hunting instinct serves little purpose but to end prematurely the student's sci- entific curiosity. If we rest content with the description of the hunting instinct as the unlearned behavior of a carnivorous animal which results in his securing food, we certainly add nothing to anyone's information when we say that animals secure food by means of the hunting instinct. Such an expla- nation is of the sort given byMoliere's physician when he says that opium puts one to sleep because it possesses a soporific property. It we are going to make use of "instinct" in the de- scription of behavior, the terms must apply to specific reaction tendencies. In civilization man has wrought so many changes in his habitat and established so many rules and conventions, that the primitive world for which he was originally adapted has in INSTINCTS 45 many cases ceased to exist. On account of this we find many maladjustments of man toward his present environment. Lying, stealing, murder, and discourtesy all have their basis in original human nature, and the theologians are quite right in their dogma of original sin. Although some of man's original responses occasion mal- adjustment in an artificial culture, others are appropriate to both savagery and civilization, and still others may in civiliza- tion be put to new uses. This is true in the domestication of animals as well as in the socialization of men. When the hunt- ing dog leaves canine and enters human society, his old trick of turning back the quarry to the pursuing pack is taken ad- vantage of by his master and serves a new purpose. The same is true of retrieving, which can be taught only to a dog that al- ready possesses the retrieving mechanism. Man first shows generosity and kindliness in general to his family group because his early childhood is spent at home. The attachment of these response tendencies to the father, mother, brother, sister — situation makes it useful to employ family names to elicit these friendly responses toward society when the child becomes an adult and leaves his home. Hence we have the terms "brother man", "brother Elk", "little brown brother", "less fortunate sister", "sister republic", "mother church", "the greatest mother of all", "mother country", "fatherland", "city fathers", "father of his country", and many others. Because the husband-wife relationship does not exist for the child, these terms do not elicit responses of the sort just mentioned, and are not found to have this derived meaning in popular speech. The foregoing is more an analogy than an illustration of the way in which original responses may be put to new uses, as the child's responses to the family are actually learned, but learned in early infancy and in situations which are common to all men. These responses are therefore practically as universal as original reaction tendencies. No matter how much man modifies his conditions of life, 46 INSTINCTS the human nature of babies remains the same ; and though man may build up elaborate machinery of law and custom for con- trolling his natural tendencies, in the race these original ten- dencies remain the constant and fundamental determiners of behavior, while conventional restrictions differ with time and place. There is no evidence for the common supposition that the neurological habits of parents are passed on to their children in the form of instincts. There are, however, many experi- mental results which demonstrate conclusively that certain of the parents' acquired characteristics are inherited by the offspring. All these inherited bodily modifications, such as congenital syphilis or transmitted malnutrition, are of a sort quite distinct from the neurological changes involved in habit formation, and offer no evidence for the belief that education is inherited. Children descended from generations of Eng- lish-speaking ancestors are probably no quicker in learning English than are babies of foreign extraction. Individual Differences Everyone recognizes the fact that in a group of horses or cows or chickens one individual differs from another. Some horses are naturally faster, and some are naturally slower. One cow is a good milker and another cow gives but little milk, even though both have had the same care and feeding. Chickens vary in size and in the number of eggs they will lay. Even in the case of men we recognize differences in height and in pigmentation which are due to endowment and not to nature. It is a tendency of our own times to be less willing to admit that from birth one man differs from another in intel- lectual ability. To a very great extent, however, we are born and not made. Some men are gifted with brains, and some are handicapped by a natural inferiority for which no amount of training will compensate. The great majority of people in INSTINCTS 47 the world could never graduate from college, because of their inadequate intellectual endowment. There are very few college students who can run the hun- dred yards in 10 seconds, more who can do it in 11, still more who can do it in 12, and probably about an equal number who can do it in 13. From this point on we find fewer and fewer students whose fastest time is 14, 15, 16, or more seconds. If an unselected group of students were to start together to run the length of a football field, they would be strung out at the finish in some such way as shown in Figure 14. -# "* * ** T*&S%$&-*^i J; n sec 7 "TT- *•*■*•£. *■ +*Z. n sec ma,v\ it sec. men 13 sec. \% sec. wen men li sec. men iosec. ma Figure 14 — Their distribution according to speed might be repre- sented graphically as in Figure 15. / / \ X- * \ Figure 15 — Surface of frequency showing the distribution of the runners of Figure 14 according to their time in seconds. It is possible by the use of mental tests to measure with but slight error the amount of a man's innate intellectual ability, and to compare the amount of this natural endowment with that of people in general. If we were to give our group of students mental tests, we would find a few of them to be conspicuously bright, more of them to be a little less intelligent, a great many of them bunched about the point of average performance, and fewer and fewer at points lower and lower 48 INSTINCTS in the scale. Such a measurement of the intelligence of stu- dents is represented in the following graph : Score m Alpha test Figure 16 — Distribution of scores of 2010 students at the University of Wash- ington in the army intelligence test Alpha. In general, bright parents have bright children, mediocre parents have mediocre children, and dull parents have dull children. Striking exceptions to this rule should not be given undue weight. The handicap of ill health, poverty, or lack of educational opportunity, or the advantage of excellent training have some effect upon the score which an individual makes in intelligence tests. This effect, however, is relatively slight. CHAPTER 3 LEARNING Although all babies start life with much the same capaci- ties, we find them as adults displaying various individual abilities which have been gained through practice and educa- tion. They have become judges, farmers, carpenters, editors, burglars, and politicians. Each has developed skill along cer- tain lines . Psychology must explain how these diverse habits are developed. We seldom observe in adults an elaborate act which is a pure instinct, and this is because the original structure of the nervous system changes as a result of use. We must not, however, fall into the error of supposing that when any response is modified by learning, it thereupon ceases to be instinctive. The instinctive components of any act may be dis- cerned, no matter how greatly it has been transformed by training. The modifications of instinctive behavior which result from use are of two sorts. A response may be aroused by a stimulus which did not originally provoke it, and the degree of ease with which any response is elicited may be altered. As a consequence of these changes, we may have a collection of instinctive movements fused together into what is called a habit. We shall first consider the modifications in the ease with which responses are brought about, and later, under the heading "The Conditioned Response", we shall discuss the attachment of responses to new stimuli. Positive Adaptation Repeated working of a stimulus-response mechanism, especially if the stimulus is just above the threshold of re- sponse, results in lowering the threshold, in decreasing the (49) 50 LEARNING reaction time, and in increasing the energy with which the response is given. This effect of repeated working is called positive adaptation. Because of practice, the lookout on board ship is able to signal the approach of a vessel more readily than is the lands- man who stands beside him. If the situation is such that we always get up when the alarm clock rings, the clock may be moved farther and farther from the bed on successive nights until we are finally aroused by a sound much too faint to have gotten us out of bed on the first morning. A physician may develop a positive adaptation to the telephone at night, while his wife sleeps through the disturbance. His wife, on the other hand, is often the only one who responds to the crying of the baby. The suburbanite develops a sensitive ear to the whistle of the early train; the bank teller is quick to detect counterfeit money; the woodsman notices signs which escape the city dweller; and all of us turn when a dime is dropped even on a noisy street. If we were to see two signboards side by side and lettered in the same type, one bearing the words BULL DURHAM and the other the nonsense words RAHD LULBUM, and if these were just near enough to enable us to read the first of these signs, we would not be able to decipher the second, though the same letters occur on the two signs. We do not develop positive adaptation to all stimuli that act upon sense organs, but only to those that provoke a response. When we first learn to perform an act in response to a new stimulus, the time involved in giving the response is much longer than it is at a later period, after practice. This short- ening of reaction time is best studied where a large number of stimuli are responded to in novel ways, as in learning to typewrite, to send or receive telegraphic messages, to translate a foreign text, or to take dictation in shorthand. By measuring the performance of any of these acts during successive prac- tice periods, and by plotting these measurements, we get what is called a practice curve. LEARNING 51 In telegraphy the practice curve for either sending or re- ceiving shows that more and more words may be handled in a given time as practice continues. There is, of course, a limit to such improvement, and the telegrapher finally approximates his maximum speed. As this limit is approached the curve flattens out. Thus the first part of practice is relatively more fruitful than the last part. 1 Through use, the tendency of a response to follow its stimulus becomes better established. This greater tendency to sequence is shown not only in a lowered threshold and a shortened reaction time, but in an increased resistance to dis- traction. The practiced act is performed in the face of altered conditions and in spite of internal variations which would orig- inally have prevented the reaction. Positive adaptation is gradually lost after practice has been discontinued. This slow disappearance of positive adap- tation is called forgetting, and may be measured just as the appearance of positive adaptation may be measured. The rate of forgetting as graphically represented is at first rapid. As time passes, the loss of practice effects takes place at a slower rate, and even after years of disuse, a stimulus-response mech- anism may still show traces of positive adaptation. Anyone who has narrowly escaped being struck by light- ning shows a greater fear response than before to the distant thunder storm. If we have been provoked to anger by another's outrageous act, he may arouse our anger again by the most trivial discourtesy. This might at first seem to be evidence that positive adaptation results best from reponses to intense stimuli but this is probably not so. It requires a very intense stimulus to call out an extensive, diffuse, and complete emotional response, although parts of the response may be given to a weak stimulus. Once the re- sponse has been called out in its entirety, the elements origin- 1 Thomdike, Notes on Practice, Improvability, and the Curve of Work, Amer. Jour. Psychol., 1916, pages 550-565. Hill, Rejall, and Thorndike, Practice in the Case of Typewriting, Ped. Sem., 1813, pages 516-529. Lashley, The Acquisition of Skill in Archery, Carnegie Inst., 1915. 52 LEARNING ally having high thresholds are more easily elicited and the act as a whole is bound together by what we shall later call conditioning. This explains why a child who has been thor- oughly frightened shows cowardice on slight provocation. His entire fear mechanism has been called into action and the partial fear response, which is ordinarily given by children who have never known abject fear, gives place to a more com- plete expression upon insignificant occasion. The child who has often been teased to a point of rage, shows positive adapta- tion of those parts of the rage response which are naturally more difficult to elicit, and thus develops a bad temper toward small grievances. Negative; Adaption If a subliminal stimulus is repeated with gradually in- creasing intensity, the response may not occur when the stim- ulus reaches or even passes the usual threshold point, and in this way, especially if the response is never given, the thres- hold of response may be permanently raised. This is called negative adaptation. If the temperature of the room falls gradually we fail to notice it, but if for any reason it suddenly becomes cold we react to the change. If the cost of living were to double over- night there would be public disorder the next day, but, because the doubling is a gradual process occupying several years, the situation remains below the threshold for rioting. The physic- ian is inured to the suffering of others by witnessing it repeat- edly, and by the necessary inhibition of any useless expression of sympathy. A child who is afraid to sleep without a light may become adapted to sleeping in entire darkness by a grad- ual reduction of the intensity of the light on successive nights. The practised person while using a microscope, shows negative adaptation for stimuli affecting his left eye. The disobedient child is indifferent to his parent's call because he has failed to respond on many occasions. In order to train a dog to come LEARNING 53 when called, the expert dog trainer never uses the dog's name except in summoning him. The visitor in a household is dis- turbed by the children's noise, while the parents may have become adapted to it. Many parents also become negatively adapted to their children's questions and are surprised when their attention is called to this. James thought it unfortunate that man is endowed with a fear response, the severity of which often renders him help- less in the face of danger. 2 Nearly anyone, if he were com- pelled to walk an I-beam high above the street, would be seized by panic and would fall. But James overlooked the fact that this original over-supply of fear is of value when it is ulti- mately decreased by negative adaptation to the dangerous situation. If fear were not found in excess in the ingenuous man, the danger-adapted man would often die of foolhardi- ness. Excessive embarrassment handicaps the adolescent in the presence of strangers, but we all dislike the adult in whom negative adaptation has been so thoroughgoing as to leave no traces of reticence. A man is saved from feeling distaste for his ageing wife because wives grow old gradually, and he becomes negatively adapted to characteristics which, were they to occur suddenly, would discourage his affection. The proper way to break a horse to the saddle is to accustom him first to a blanket, next to blanket and surcingle, then to the saddle in addition. Later, to adapt him to the pressure of the rider, a bag of feed of gradually increased weight may be strapped across the saddle. Successful breaking depends upon keeping the stimuli within the horse's growing toleration. A disliked food taken in quan- tities sufficiently small to excite no disgust, may be eaten in gradually increasing amounts on successive occasions until a large portion does not cause aversion. Crowding the thres- hold for intolerance of a stimulus, without reaching the break- ing point, makes for increased tolerance. 2 James, Principles of Psychology, Vol. 2, page 419. 54 LEARNING Another way in which negative adaptation may result is by the failure of the response, though given, to rid the animal of the stimulus. In such a case, the stimulus-response mechanism becomes fatigued, and the response is given less and less energetically to the persistent stimulus, until all response ceases. The horse which is broken by the cow- puncher method becomes accustomed to the saddle when his efforts to dislodge it repeatedly fail, and so, while he may always make slight movements of resistance while being saddled, the threshold of resistance is permanently raised. We have said that negative adaptation may be brought about in two ways. The repetion of a subliminal stimulus may cause it ; or it may result when a stimulus persists in spite of the animal's responses, after fatigue has raised the threshold. There is a third kind of situation which results in negative adaptation. An eliciting stimulus may be rendered ineffective by the presence of an inhibiting stimulus, and, the threshold of response being thus raised, negative adaptation results. In this way children become negatively adapted to temptingly accessible food by the inhibiting threat of punishment. In Triplett's experiments, perch were separated from minnows, which are their natural food, by a glass partition in the aquarium. Aperch would at first dart toward a minnow, but would strike its head against the glass. In time the big fish became negatively adapted to the presence of the minnows. The partition was then removed and the minnows mixed safely with their natural enemies. This case, though an example of negative adaptation, involves habit formation and this will be discussed below. 3 Both negative adaptation and summation follow upon the repetition of subliminal stimuli, though they are quite different results of such repetition. It is the length of the intervals between the stimuli that determines which one of these two effects will occur. A series which will have a summation 3 Triplett, The Educability of the Perch, Amer. Jour. Psychol., Vol. 12, page 354. LEARNING 55 effect, and finally bring about a response, may lose that effect if the length of the intervals between stimuli is increased, in which case negative adaptation, or the permanent raising of the threshold, takes place. These alternative possibilities are seen not only in behavior but in the physiological responses of the body to drugs. If one dose rapidly follows another, a cu- mulative effect results, but if gradually increasing doses are given at widely separated intervals, negative adaptation, results, so that the patient may come to tolerate amounts of the drug which would have been fatal at the outset. Transitory Changes or Threshold During a Single Practice Period If a considerable time has passed since an act was last performed, the threshold of response is found to be unusually high and the reaction time to be unusually long. When a ball player begins his day's practice he is less sensitive to situations and slower to respond than he is after fifteen- minutes of warming up. In golf we take a few practice strokes before driving from the first tee in order to pass this period of slug- gish reaction. The slowness and the weakness of response and the high threshold that characterize the beginning of any activity we shall call initial torpor. 4 Initial torpor is seen in simplest form in the contractility of the muscle-nerve preparation or in a spinal reflex. When it is exhibited in such a complex act as game playing or factory work, other elements enter in to make it appear greater than it really is. When work has first begun, negative adaptation to distraction has not yet occurred. Passers-by, noises, and room temperature, all disturb us at first, but later, through negative adaptation, are disregarded. Another obscuring factor is the hangover of responses recently given. Conversation just engaged in leaves the talker for some time afterward still talking to himself. If we turn from chess to letter writing, a tendency to make chess moves 4 Thorndike, Educational Psychology, Vol. 2. 56 LEARNING hampers the composition of our first paragraph. The student who has hurried to avoid being late at class is agitated for some time after taking his seat. This hangover of recent movements is due partly to the persistence of emotional re- cnforcement. A complex habit is made up of many parts and involves many action systems. Initial torpor attaches to each part and to each emotional reenforcement. It is dissipated in the parts of lowest threshold before it disappears in others. As one part after another of the entire act is brought into play by tentative beginnings, and by the stimuli which these begin- nings bring to bear upon us, the several parts of the act suc- cessively lose their sluggishness and combine into the act as a whole. After such warming up the entire habit has a lowered threshold. Every time work is begun after a long period of rest, initial torpor is found to be present. If the practice curve is still rising and has not reached a plateau, the absolute amount of initial torpor to be overcome is less at the beginning of each successive practice period. There is no difference in kind between the positive adaptation shown in overcoming initial torpor and the positive adaptation which is the gradually decreased reaction time and lowered threshold of an act prac- ticed at intervals for many days and graphically represented by the practice curve as a whole. Toward the end of the doubleheader the ball player again becomes less sensitive to situations and slower in response, and this we call fatigue. Toward the end of the shift in the factory the number of accidents increases. 5 The third time around the links we make a poor score. Fatigue is the slowness of response, the weakness of response, and the high threshold of response which finally occur if any activity is continued long and vigorously. It is a temporary effect of repeated action, and a period of rest causes it to vanish. 8 5 Uoldmark, Fatigue and Efficiency, Russell Sage Foundation, 1912, page 71. 6 Thorndike, Fatigue in a Complex Function, Psychol. Rev., 1914, pages 402-407. LEARNING 57 Figure 17— Distribution of German industrial accidents throughout the working day, showing fatigue. (After Goldmark). The Conditioned Response How may a response be provoked by a new stimulus ? Let us take the case of a dog that sees a cat. On seeing the cat he barks. Suppose that while looking at the cat he hears his master say the word "cats", and that these two stimuli occur together several times. Later if he hears the word "cats", although there is no cat present, he will bark. This response originally called forth by the sight of a cat is now provoked by a new stimulus, namely, the sound of a word. When a response is elicited by a new stimulus, due to the fact that the new 58 LEARNING stimulus has occurred along with the old, it is called a condi- tioned response. If a percussion hammer falls upon the patellar tendon, a spinal reflex is elicited involving the contraction of the quad- riceps muscle. This is called the knee-jerk. In 1902, Twitmyer demonstrated that if a bell was sounded each time that a ham- mer fell on the patellar tendon, it was possible, after consider- able practice had occurred, to elicit the knee-jerk by the audi- tory stimulus alone. 7 Today a reflex response to a substituted stimulus is called a conditioned reflex, because the substituted stimulus is always one of the conditions accompanying the original stimulus. Pavlow discovered that a conditioned sal- ivary reflex could be secured from dogs. Certain foods, when eaten, cause a copious secretion of the salivary glands. He found that, if some visual or auditory stimulus is made the invariable accompaniment of the saliva-exciting food, the accompanying condition will provoke the salivary flow in the absence of the original food stimulus. Watson and Lashley demonstrated the conditioned salivary reflex in man as well as other conditioned reflexes in both dogs and human beings. 8 The principle that one of the accompanying conditions of a stimulus responded to may later become a substituted stim- ulus for the response, applies to all associative learning. If a bell is attached to a dog's tail and the dog is petted in a way to make him wag his tail, the sound of the bell will be a con- stant condition under which the caudal response is elicited. After considerable wagging of the belled tail the bell may be removed and the wagging produced without petting when the dog hears the bell rung. In order to make a dog respond to his name when called, the trainer secures this response first to food and then, while the dog is coming, speaks his name. In time the sound of the name becomes the substituted stimulus for approach. 7 Twitmyer, .4 Study of the Knee Jerk, Phila., 1902. 8 Watson, Psychology, pages 29-38. LEARNING 59 If a number of photographs are presented to a subject, each one being named by the experimenter and then by the subject as he looks at the photograph, a conditioned response will in time be established toward each picture, so that the subject will call it by the proper name. The previous stimulus for this response was the word spoken by the experimenter, and the substituted stimulus is the accompanying visual repre- sentation. In like manner probably any response may be con- ditioned by accompanying stimuli in the absence of the original stimulus. Nausea may occur at the mere sight or odor of food in which a nauseating medicine was once taken or which was eaten during a storm at sea. This fact was made use of in curing the whiskey habit. Mark Tvvain found it difficult to speak on serious matters in public because he himself con- stituted a conditioning stimulus which always provoked laughter in his audience. 8 Conditioned Emotional Responses An interesting example of a conditioned response is seen in the attachment of an emotional expression to some situation which originally had no power to bring out the emotion. Pro- bably each emotion is originally provoked by a very limited number of situations. Tickling is the adequate stimulus for causing the baby to smile, but the baby may learn to smile at sight of the person who has tickled him because he has been exposed simultaneously to the tickling and to the sight of the tickler. He is not originally afraid of the sight of a dog and indeed will ordinarily reach toward it, but once frightened by its bark or knocked down by its rush the subsequent sight of the dog is sufficient to cause the expression of fear. 10 The dog once kicked by the milkman will fly into a rage at sight of him, his rage response being originally provoked by the kick, but conditioned by the appearance of the man. 9 Interesting examples of conditioned emotional responses are described by Locke in his Ettap Concerning Human Understanding, Book 2, Chapter 33. 10 An experiment in establishing conditioned emotional responses in an infant is described by Watson and Rayner, Conditioned Emotional Reactions, Jour. Exper. Psychol., 1920, pages 1-14. 60 LEARNING It is in this way that we learn to show anger, joy, fear, love, disgust, and other emotions in response to those occur- rences of life which are apt to be followed by events that make these responses appropriate. Thus we anticipate the attack of a familiar foe, or by an early withdrawal avoid too close contact with the frightful object. Many of our fears, likes, or dislikes are conditioned responses to stimuli which have only a chance temporal connection with their natural provoca- tion. A celluloid collar in itself is neither alluring nor repul- sive, and our dislike of such an article of dress is dependent upon the fact that we have always experienced it in connection with a wearer who is not too scrupulous as to his personal cleanliness. Everyone builds up a set of emotional tendencies through this process of association, so that his adult attitude toward the experiences of life is fitted to the culture into which he has been born. Particular melodies become associated with the words of songs and with emotional expressions which have been called out by these words. Although at first only the words may have had the power to arouse the emotions in question, the music itself, in the absence of the words, will later have the same effect. Easter and Christmas music, the melody to which sentimental words were sung, patriotic airs, the words of which originally excited patriotic emotions, or the music sung at the funeral of a friend, will long afterward revive the emotional expression of which they were at first the incidental accompaniment. Conversely, music itself may directly arouse emotional responses, and this fact is made use of to reenforce the conviction which the attending words but partly establish. The stirring airs of the camp meeting or the patriotic rally bring many to the mourner's bench or the recruiting office who would remain sinners or slackers if appealed to by words alone. Emotional expressions as a whole may be attached to new stimuli and in inappropriate situations constitute many of LEARNING 61 the psychoneuroses. If in the process of courtship a person is placed in a position to arouse great fear, the emotion of fear may become attached to all erotic stimuli, and what is known as an anxiety neurosis may develop. Cases have been reported in which an aversion for small rooms can be attributed to the subject's having fainted at one time in a small close room ; in which a fear of buzzing insects followed a child's being frightened by a humming bird which entered a window and flew rapidly about the child's head ; in which a horror of bells was caused by a church bell's ringing at the same time that great depression, resulting from her mother's death, possessed the subject, who believed herself responsible for her mother's illness. Such conditions often call for treatment at the hands of a psychologist. The way in which these bad habits of emotional response are cured is to attach a rival response to the stimulus which arouses them. If, for example, a person shows a morbid aver- sion towards touching absorbent cotton, the psychoanalyst at- tempts to discover the origin of this response by delving into the subject's past. It may be found that as a child the subject once handled some dirty cotton which had been used as a sur- gical dressing, and that he was at that time scolded by a dis- gusted parent. For practical purposes it probably does not matter whether this event was the original occasion for the subject's distaste for cotton, provided the subject is himself convinced that this was the real cause. With this start, the psychoanalyst proceeds to lower the threshold for the recol- lection of this childhood event, and so makes certain that the subject will always think of the event when cotton is seen. The subject is then told that little children can not be held responsible for failure to avoid unsanitary acts, that the sub- ject himself was in no way to be blamed for what he did, that certainly no harm resulted from his act, and that, indeed, the whole matter is very ludicrous as we look back upon it. 62 LEARNING In this way there becomes attached to the sight of cotton the tendency to discuss the childhood event and for such dis- cussion to be accompanied by self-satisfaction and amusement. If this line of response is sufficiently practised and sufficiently reenforced by verbal rationalization, it develops a threshold which is lower than that of the aversion response, and thus the aversion habit is cured. An act may be learned in response to one situation and later given to another which is partially identical, even though the common elements in the two situations are wholly inci- dental and irrelevent. This substitution does not involve the process of conditioning. It is nicely illustrated by many false moves in everyday life. The following cases have been re- cently observed. A person was about to make tea. Instead of turning on the gas for the bunsen burner, lighting it with a match, turning on the water faucet, filling the kettle, and plac- ing the kettle over the burner, he made the mistake of turning on the water, lighting the match, and placing the match under the faucet. The mistake was, of course, due to the similarity of proprioceptive stimulation involved in turning the gas cock and opening the water faucet, t\ie false response being practi- cally the same as the gas-lighting response. Another example of the substitution of one stimulus for another, due to partial identity, was found in the case of a man who entered a shop to purchase a newspaper and who dropped his money on the floor. He picked up the money and left the shop without secur- ing the paper, and did not appreciate his mistake until he was some distance away. Here the responses of picking up the coin and of picking up the newspaper are almost identical, and the mere act of picking something up was the usual stimulus for leaving the shop. Facilitating Effect or Conditioning Stimuli If a dog that has been trained to respond to the word "cats" sees a cat at such a distance that the stimulus is below LEARNING 63 the threshold for chasing, his master may urge him on by- using the word and he may at once start in pursuit. In this way the sound of the word "cats", although not now the sole cause of the response, facilitates the response, because it occurs in conjunction with the actuating stimulus. Illustrations of these conditioning stimuli and their re- sulting facilitation are plentiful in everyday life. The literary man accustomed to writing while smoking a pipe finds it dif- ficult to work without the pipe in his mouth. The person habituated to evening clothes dines with greater ease when correctly dressed. The clergyman is moved to greater elo- quence when wearing his cassock, and would find it difficult to preach a sermon on the street corner. The college instructor, because he frequently uses chalk during lectures, finds facili- tation to his speech through holding a piece of chalk in his hand. Our familiar surroundings increase our personal effic- iency, and this law gives a psychological justification to the so called right of personal property. A man sleeps best in his own bed, not only because he is negatively adapted to the distracting stimuli of his neighbor- hood, but because he has gone to sleep many times in these surroundings and they have a facilitating effect in producing slumber. A child often refuses to sleep unless covered by a familiar blanket, or allowed to suck his thumb, or permitted to take a certain doll to bed with him. Neurae Basis of the Conditioned Response Conditioned responses involve the formation of new pathways and the possibility for this is best afforded by the intricate association fibres of the cortex. When a neural arc is acting, impulses received from sense organs not previously connected with this neural arc are likely to be drained into its outgoing motor pathway. This drainage establishes new syn- apses and thus connects new sense organs with the responding 64 LEARNING muscle. This is the neural basis of the conditioned response. This may be best understood by consulting the diagram in Figure 18. MujtltJ Figure 18 — Establishing a conditioned response. The first stimulus which sets the dog to running and barking is the sight of the cat. If, at the same time, he is stimulated by the word "cats" pronounced by his master, the impulses resulting are drained into the system which is acting, and a pathway is established. After practice, this sound becomes the conditioning stimulus which may set the dog into activity in the absence of any cat. LEARNING 65 Impulses aroused by accompanying conditioning stimuli re drained into the motor system which is active at the time, "hus when the original stimulus and the conditioning stimulus ct together the combined energy from the two is drained into single motor system. For this reason the conditioing stimu- xs facilitates the action of the original mechanism and this lay act with less intense stimulation than was first required. The Serial Response Each movement a man makes is likely to bring him into ew relations with his surroundings and thus cause new stim- li to act upon him. In this way a stimulus produces a re- ponse, this response a new stimulus, this stimulus a new esponse, and so on until the man reaches a place where there re no more stimuli which cause movement. If such a series > repeated many times the man's responses show positive daptation to each of the several stimuli, so that the time equired for going through the series of responses is short- ned. Entering our own house is an act which we all perform moothly and quickly. The first time we entered the house, owever, we were less quick in opening the gate and in closing after us, slower in mounting the unfamiliar steps, finding the ey, and unlocking the front door. As we repeat the act day fter day bur entrance takes less and less time. This increase 1 speed is in part a simple positive adaptation of response to le successive stimuli of gate, steps, key, and lock. In addition to the stimuli which affect our eyes and to ■hich our responses are given, there is another series of stim- li which the responses themselves cause and which accom- any the visual stimuli. These are stimuli to the propriocep- :>rs in the muscles and tendons caused by the movements of lanipulation and walking, and the stimuli to the end organs f touch which these movements occasion. These movement- roduced stimuli play a role similar to that of all other stimuli -hich are incidental to the actuating stimulus, in that they -3 66 LEARNING serve to condition the response when the actuating stimulus is absent, or to facilitate the response when the yoccur time after time along with the actuating stimulus. This facilitation is a cause for the increased speed of the serial reaction in addition to the positive adaptation mentioned above. In the same way a person learns his way about the house, at first depending upon his eyes to avoid obstacles and to find the easiest route from place to place As all movements are accompanied by proprioceptive stimulation, in time he is able to dispense with visual stimuli and to find his way about in the dark. Tying a cravat or lacing a shoe is at first dependent upon visual stimuli, but later each component movement be- comes almost wholly conditioned by the kinaesthetic and touch stimuli occasioned by the preceding movement. A pianist while learning a musical composition depends upon his score as a guide in making each movement. Later, because each move- ment becomes the cue to the next, due to its stimulation of sense organs in the muscles, and due to its producing sounds which stimulate the ear, the 'musician may throw away his score. If a printed page is read aloud many times the book may be closed and the passage spoken from memory. This is in part the result of the sound of each word becoming the con- ditioning stimulus for the movements producing the next word, and in part the result of the accompanying kinaesthetic stimulation playing a similar role. In learning to write we first depend upon copy books, but later, in addition to the conditioning proprioceptive stimulation, the sight of the first letter of the familiar word which the pen forms becomes a conditioning stimulus for writing the second letter and this is a conditioning stimulus for the third and so on. 11 When a person is learning to dance he makes one move- ment after another in response to each verbal direction of his instructor. While one movement is being made the instructor gives directions for the next, so a proprioceptive stimulation 11 On the neutral basis of chain reflexes and serial responses see Herrick, Introduction to Neurology, and Sherrington, Integrative Action of the Nervous System, page 181ff. LEARNING 67 C V" c 'igure 19 — Diagrammatic representation of the chain reflex mechanism (after Herrick). C, synapses in nerve centers. E, effectors. R, receptors. The action of each effector results in the stimulation of an adjacent receptor. The stimulation of each receptor results in the action of an effector. :aused by the preceding movement accompanies the instruc- or's verbal stimulus. With repetition of the stimulus-re- sponse series, these proprioceptive stimuli become condition- ng stimuli and serve to link together the responses in the ibsence of verbal direction. When this dependence of each novement upon the muscle stimulation of the preceding move- nent occurs, we say the person has learned to dance. The way n which this substitution of movement-produced stimuli for he original exteroceptive stimuli comes about is illustrated in "igure 20. The facilitating effect of accompanying conditioning stimuli is seen in what might appear at first sight to be cases I Receptors Muscles and Proprioceptors '-IJL 'igure 20 — Diagrammatic representation of the formation of a serial-response habit. (After Dunlap). The series of responses is at first the result of the successive stimulation of the distance receptors shown at the top of the figure. During practice this stimulation is accompanied by the stimulation of pro- prioceptors in the acting muscles. This proprioceptive stimulation gives rise to nervous impulses which are drained as indicated by the arrows into the acting system and in time the series of responses may be elicited by these movement-produced stimuli, only the first of the distance receptor stimuli being necessary. 68 LEARNING of simple positive adaptation. Thus positive adaptation to the alarm clock is shown by the conscientious person who, always responding, is eventually stimulated to rise by the faintest tinkle. He is aided in rising, however, by the fact that his first start of surprise has been followed by the movement of his arm in throwing off the covers, and this in turn by sitting up, feeling for his slippers, putting them on, and rising to his feet. When this series of movements is made, the propriocep- tive stimuli occur in a certain order and become conditioning stimuli which serve to fix the sequence of responses. Positive adaptation plays its part in speeding up each step in the chain reaction, but the most important factor in maintaining the response as a whole is the series of conditioning propriocep- tive stimuli. Such conditioning stimuli as are mentioned above are in- volved in the movements themselves, and are not subject to the vagaries of the external environment, Hence they serve to stereotype the response as a whole in a way which would not be possible if the organism had to depend for guidance wholly on external situations whose regular occurrence is uncertain. These orderly response series, now partly independent of the environment, constitute most of our skilled acts and enable man with his aptitude for such habit formation to dispense with the fixed instinctive order of responses characteristic of the behavior of the lower animals. This is not because man has more proprioceptors or other sense organs than have lower animals, but because in man these sense organs have more extensive connections in the central nervous system. The re- sulting plasticity enables man to adjust himself to various cultures, occupations and environments. The Effects of Practice on the Serial Response The effects of practice in establishing a serial response have been measured by Ebbinghaus, who determined the num- ber of repetitions necessary for learning a series of nonsense LEARNING 69 yllables so that it might be reproduced once without error. By i nonsense syllable is meant such a sound combination as nis, ; - eg, fof, gol, nen, kev, and so forth. 12 The longer the series, the greater is the number of repe- itions required for learning. Ebbinghaus could repeat a se- ies of seven syllables after having said it once, whereas a eries of 12 syllables required about 16 repetitions, a series >f 16 syllables required 30 repetitions, one of 24 syllables, 4 repetitions, and one of 36 syllables, 55 repetitions. These .re represented in Figure 21. L£NGTH OF SERIES igure 21 — The number of repetitions required for establishing serial responses of various lengths. The material learned consisted of series of nonsense syllables. A repetition consists of saying any series once, irrespective of the length of the series. The syllables were spoken at the rate of 150 a minute. (After Ebbinghaus). 12 See: Lyon, Memory and the Learning Process; Meumann, Psychology of Learning; and bhinghaus, Memory. 70 LEARNING These results may be stated in another way, namely, ir terms of the actual amount of work done to learn each series Repeating 12 syllables 16.6 times involves pronouncing 19< syllables; repeating 16 syllables 30 times involves pronounc ing 480 syllables ; repeating 24 syllables 44 times involves pro nouncing 1056 syllables; and repeating 36 syllables 55 time: involves pronouncing 1980 syllables. If we plot these value: L '!■ V !!V'j DM uiijmu Figure 22 — The same results are shown as in Figure 21, but are represented ii terms of the actual amount of work done in order to learn the series o various lengths. Except for series of less than 12 syllables, the work re quired is a linear function of the length of the series. LEARNING 71 •aphically we find they lie approximately on a straight line, figure 22). This means that as we pass from one series to another, e difference in the work required for learning is proportional the difference in the lengths of the series learned. If the syl- bles are repeated at intervals of .4 sec, or in other constant lythm, the time consumed will be proportional to the number syllables spoken. If we prepare series of nonsense syl- bles of totally different material and of different lengths, •ntaining 16, 17, 18, 19, etc., syllables respectively, and find at 16 syllables are learned in 3 minutes and 17 in 3^2 min- es, then the series of 18 syllables will be learned in 4 min- es, the series of 19 syllables in AVz minutes, the series of ) in 5 minutes, and so on. It will then take 13 minutes to learn series of 36 syllables. Even though it may be impossible to remember tomorrow hat we have learned today, today's learning makes tomor- iw's relearning easier. The amount of positive adaptation re- aining from previous practice may be measured by the num- :r of repetitions saved when material is learned over again, his method of measuring retention has become known as the ving method. Ebbinghaus, using a number of different 16 syllable se- ss, repeated some 8 times, some 16, some 24, some 32, some I, some 53, and some 64 times. Twenty four hours after each ie was practiced he found the number of repetitions neces- ry for relearning it. In this way he discovered that each one ' any number of repetitions produced the same amount of re- ntion as any other. It happened that, for the length of series led, each of the original repetitions saved the next day one :rcent of the time that would have been required if there had :en no previous practice. Thus 8 repetitions saved 8.1 percent : the next day's work, 32 repetitions saved 32 percent of the :xt day's work, and 53 repetitions saved 53.9 percent. The .tigue resulting from many repetitions made it impossible to .rry the experiment beyond the point of 64 repetitions. Ex- 72 LEARNING cept for this, 100 repetitions would probably have made it pos- sible to reproduce the series the next day without any review. It will be remembered that to learn a series of 16 syllables, so that it may be repeated once without error immediately after the learning, requires about 30 repetitions. Figure 23 shows the relation between the first day's practice and the next day's relearning. Forgetting If a given amount of material is memorized, we may measure the amount retained in memory at any later time by finding the length of time which is required to relearn the ma- NUMBER * *EPETlf?ONS 48 Figure 23 — The time saved in relearning a serial response of 16 nonsense syllables shown as a function of the amount of yesterday's practice. The amount of positive adaptation found at the time of relearning is a linear function of the amount of work done 24 hours earlier. (After Ebbinghaus). LEARNING 73 terial. The time saved in relearning, compared with the time required for the original learning, gives us a quotient which stands for the proportion retained in memory. By this method it is shown that the memory deteriorates as time goes on, and that the rate of deterioration is most rapid at the outset. This rate of forgetting as measured by Ebbinghaus is shown in* Figure 24. Meumann and others report what they take to be a slight recovery of memory at the end of 24 hours. 13 This anomaly was not shown in the careful work of Ebbinghaus though a tendency to such recovery may be noticed in Figure 24. Meu- mann's subjects were unable to recall as much 9 hours after practice as they could recall 13 hours later. Graphically re- presented, there was a rise in the forgetting curve between the 9 and the 24 hour points. Many suppositions have been made on the basis of these results. Colvin says "This improvement in memory seems to be due to the fact that the original impres- sions have had an opportunity to become associated with per- manent elements in consciousness, and, therefore, are capable of revival more readily after a certain lapse of time." 14 From the following experiments by Mr. W. R. Wilson in the local laboratory an interpretation of Meumann's results in terms of the facilitating action of conditioning stimuli is suggested. Ten subjects learned lists of ten nonsense sylla- bles, and 72 hours later relearned the same lists sometimes in the same surroundings, and sometimes in different surround- ings. Each subject learned one list in the laboratory and re- learned in the laboratory, learned a second list in the labora- tory and relearned out of doors, learned a third list out of doors and relearned in the laboratory, and learned a fourth list out of doors and relearned out of doors. In eight of the ten subjects there was greater saving in each case where re- learning occurred in the same surroundings in which the first learning had taken place. Two subjects showed in one of 13 Meumann, Psychology of Learning, Chapter 7, Sec. 6. 14 Colrin, The Learning Process, page 140. 74 LEARNING 100 do ^ 60 01 < -J LLJ Q > 20 2 UJ o q: u OL ■1. . ""H "T-;/-i '!'!■.[", i, n | !f i rrr[ ' | 1 i' ; 1 ' " ! ; j j 1 r ;j ..! . 1 [ 1 . 1 1 V I 1 1 1 jj !|!|l i!l | i |i I ! IP 1 ' 1 ■ ' 1 * 'ii> t 1 ' •.;, , ..; ' j j j ' ■ 1 ...HOURS 2\Q. k ...,;J4 A, „ ^ W* Figure 24 — The rate of forgetting a nonsense series. (After Ebbinghaus). The amount of positive adaptation remaining at any time is measured by the saving method. LEARNING 75 their four series a greater saving where relearning had oc- curred under dissimilar conditions. An average of 11.4 per cent fewer repetitions were required to relearn in similar surroundings. In another experiment the subject was seated in a room and copied a list of letters on a typewriter whose keys had been arranged in a random order. He copied the same list 24 hours later and the times were compared. A variable condition con- sisting of the presence or absence of the odor of oil of pepper- mint was used. Each subject practised a list with the odor present and repeated the same list with the odor absent; he then practised a list with the odor present and repeated the list 24 hours later with the odor present. He then practised with list without the odor and repeated with the odor; and last practised without the odor and repeated without the odor. 13 subjects were used, and the average saving in the time required to repeat the lists was 9.4 per cent greater when the repetition took place under the condition of the first practice. It is highly probable that the greater retention shown by Meumann's subjects at the end of 24 hours depended upon the daily recurrence of conditioning stimuli. There is a diurnal rhythm of experience which results in a characteristic internal state at each hour of the day. We sleep, eat, work, and play according to a fairly rigid schedule. The resulting periodic bodily states, present at the original learning, contribute fam- iliar stimuli to anyone who is engaged in relearning after a 24 hour period. These stimuli come to condition the responses and facilitate the relearning. Whole and Part Learning One of the practical questions which arises when we have something to commit to memory is whether the material should be rehearsed from beginning to end, or broken up into parts so that each part can be learned separately and the parts later combined. If the law represented by Figure 22 held for short series as well as for long, it would take twice the time to 76 LEARNING learn any series as to learn a series half that length. Part learning would then evidently be wasteful, because it would take the same time to learn by parts as to learn by wholes, and after the parts were learned the order of the parts would have to be learned also. The law (Figure 22) holds, however, only for lengths somewhat greater than the memory span. This memory span is the amount which can be accurately reproduc- ed after a single reading. Because small parts are memorized with relatively greater ease than large parts, we have no way of determining in advance of experiment whether the easy learning of small parts compensates for the necessity of link- ing these parts together after each has been committed to memory. Ebbinghaus has shown that when two series of different lengths are memorized to the point of one perfect reproduc- tion, the longer series is better retained after 24 hours than is the shorter series. Thus, 33 percent of a 12 syllable series is shown by the saving method to persist after the lapse of one day, whereas 48 percent of a 24 syllable series is retained. This fact, taken in conjunction with the law (Figure 22) that an increase in the length of the series demands a corresponding increase in the amount of work required for learning, gives us reason to expect that experimental results will show a saving when the method of learning by wholes is employed. Experimental results demonstrate conclusively that part learning is wasteful and whole learning most efficient. The whole method requires less work for a single accurate repro- duction, and for a given amount of work done results in fewer errors and better retention. This holds true for both nonsense material and for meaningful material. 1 "' Results of the Distribution of Practice If we have a certain amount of time to spend in mem- orizing, it is found advantageous to distribute this time over 15 Lyoi Wetno >• and the Learning Proce**; Pechstein, Whole vs. rnrt Methods in Motor Learning, i Monographs, 1917; Pyle, Economical Learning, Journal of Educational Psychology, i