key: cord-0203502-yagj9gkz
authors: Childs, Elizabeth; Mohammad, Ferzam; Stevens, Logan; Burbelo, Hugo; Awoke, Amanuel; Rewkowski, Nicholas; Manocha, Dinesh
title: An Overview of Enhancing Distance Learning Through Augmented and Virtual Reality Technologies
date: 2021-01-26
journal: nan
DOI: nan
sha: 550f8edb0f11a5dcb711ccf12b22df90da4b0627
doc_id: 203502
cord_uid: yagj9gkz

Although distance learning presents a number of interesting educational advantages as compared to in-person instruction, it is not without its downsides. We first assess the educational challenges presented by distance learning as a whole and identify 4 main challenges that distance learning currently presents as compared to in-person instruction: the lack of social interaction, reduced student engagement and focus, reduced comprehension and information retention, and the lack of flexible and customizable instructor resources. After assessing each of these challenges in-depth, we examine how AR/VR technologies might serve to address each challenge along with their current shortcomings, and finally outline the further research that is required to fully understand the potential of AR/VR technologies as they apply to distance learning.

Augmented reality (AR) is an emerging form of digital experience in which the user's visual perception of the world around them is augmented using a computer-generated graphical overlay. This overlay is superimposed onto the user's view through a combination of sensors and algorithms, enabling virtual components to be projected into the real world, sometimes on the lens of a head-mounted display (HMD) that the user wears. In addition to AR, Virtual Reality (VR) is a related technology that also leverages computer technology in order to create an artificially rendered digital experience, but crucially differs from AR in the fact that the visual experience of VR is entirely computer-generated, while AR superimposes digital rendering on top of the real world.

While the technical feasibility of AR and VR has existed for decades, AR and VR have only recently become commercially accessible due to the advent of mobile platforms (e.g. iOS and Android) combined with rapid advances in consumer grade hardware [72] . Applications of AR and VR have the potential to benefit many fields, but one of the most exciting and vital applications for these technologies is leveraging them in an educational context [8, 66] .

The promise of aiding learning via the addition of immersive virtual environments has been alluring, but due to the fact that education as a whole has been disrupted recently due to the COVID-19 pandemic, the importance of evaluating exactly how AR and VR technologies can improve the learning experience cannot be overstated. Distance learning, a method of studying in which lectures are broadcast or classes are conducted by correspondence or over the internet without the student's needing to attend a school or college, had also already become an integral part of many schools around the globe prior to the pandemic [19] . Greenberg defines contemporary distance learning as "a planned teaching/learning experience that uses a wide spectrum of technologies to reach learners at a distance and is designed to encourage learner interaction and certification of learning" [29] . Distance learning is a particularly promising educational application of AR and VR due to its unique pedagogical structure and existing and rabidly expanding technological dependency. AR and VR have the potential to create unique learning opportunities that allow course content to be taught and presented in ways that may have otherwise been extremely challenging if not impossible. This is of value in any form of education, but could vastly improve distance education because of the issues students regularly face in distance learning environments.

In this paper, we first assess the educational challenges presented by distance learning as a whole, and identify 4 main challenges that distance learning currently presents as compared to in-person instruction: the lack of social interaction, reduced student engagement and focus, reduced comprehension and information retention, and the lack of flexible and customizable instructor resources. After assessing each of these challenges in-depth, we examine how AR/VR technologies might serve to address each challenge along with their current shortcomings, and finally outline the further research that is required to fully understand the potential of AR/VR technologies as they apply to distance learning. Seeing as these fields are relatively new, examination of the provided tables is strongly encouraged for further clarifications on the information provided in this review.

Immersive environments blend a digital, computer generated world with the real world. They augment, or fully replace a user's perception of the spacial world around him or her, placing the user in an altered environment. The ratio of real objects to digital objects in a user's view affects the amount of digital augmentation, and was defined in Milgram's Mixed Reality (MR) continuum [49] . In the continuum, a real to digital ratio of 1:0 would be the real world at the beginning of the spectrum. As digital content is added, computer generated images are superimposed onto the user's view. The amount of digital content added to the user's view determines the program's position on the MR continuum. For example, simply text or 2D images that appear in the user's view (such as when Google Maps AR gives an arrow and street name for walking directions [28] ), would be at the lower end (left) of the continuum. Increasing the immersion, such as adding a realistic 3D couch in your living room before buying it [9] moves the application farther right on the MR spectrum. Environments that are entirely computer generated but allow the user view of certain real elements, such as a hand or select real objects, would be considered augmented virtuality. With this definition, everything with a real to digital ratio greater than 0 and less than infinity constitutes mixed reality, with augmented reality being at the lower end of the spectrum and augmented virtuality being at the higher end.

It should be noted that over time, the definitions of AR and MR have evolved since Milgram first defined the MR continuum. Conventionally, anything that is not purely real or purely virtual has been defined as augmented reality. Technically, Microsoft defines their HoloLens as mixed reality [47] to distinctly differentiate it from lower resolution AR glasses, such as the raptor [22] , which fits Milgram's true definition of augmented reality. It should be noted that for the purposes of this study, all immersive experiences except for pure virtual reality will be addressed as augmented reality, both to match the convention of similar studies and for simplicity of understanding. When the user's view is completely virtual (real to digital ratio of 0:1), the experience is considered VR. With VR, the user has no view of the real world and can only see a computer generated word that exist in the same spacial area as the real world. For the purpose of this paper, AR will be considered all devices in the middle of the MR continuum, where both digital and real images are visible, with VR being entirely virtual environments. We will consider the hand tracking and body tracking that many present day VR headsets have as completely virtual for the scope of this research, as this often appears a rendered image based on sensors.

In addition to the blend of real and digital content that defines immersive environments, they can also be categorized by the way a user experiences the digital content. Immersive Devices have control over the user's entire point of view, whereas non-immerse devices only augment part of the user's view.

Immersive devices are typically headsets, or head mounted displays (HMDs). They may include earpieces like noise-cancelling headphones to control the user's auditory field, and most HMDs incorporate handheld controllers which increase the methods of input for the immersive experience. With VR, the user actually feels transported into the new environment, and with AR, the digital information is cohesive across all of the user's visual field. In terms of education, immersive displays have been shown to increase memory recall over non-immersive displays [64] and help with information retainment.

However, immersive displays do have limitations. While inexpensive immersive displays exist, such as Google Cardboard [27] , they do not have the graphics and computing ability to offer truly immersive environments. Devices like the Oculus Quest 2 have begun to enter the consumer market due to lower price tags than what VR headsets initially launched at (i.e. as of June 14th 2021, oe can buy a 64 GB Oculus Quest 2 off of the Oculus website for $299 USD. However, when the Oculus Rift launched it was priced at $599 USD). However, the more immersive headsets like the Oculus Quest 2 may still be too expensive to bring into educational environments.

Non-Immersive devices include handheld displays, and typically use a smartphone or tablet. The user can still move around in the virtual or augmented world; however, all of the digital content is viewed through the device screen. AR and VR applications can also tap into the device's camera, gyroscope, and/or accelerometer to enhance an immersive experience. Non-Immersive devices are used more prevalently for AR education, which is discussed further in the section below.

Advantages of non-immersive devices stem mostly from their accessibility. While non-immersive devices may not have the same technical capability or depth of experience as immersive devices, over half of the world has a smartphone [2]. This makes nonimmersive devices ideal as educational tools because they are accessible, inexpensive, and relevant for current educational populations.

For example, smartphones allow the user to experience MR by altering the screen content based on the spacial location of the device. The MR content can then be viewed as a handheld device, by looking through the phone, or as a head mounted display (HMD) by strapping the phone to the face. Additionally, the device's accelerometer, gyroscope, microphone, and speaker can provide additional levels of immersion.

(a) Non-Immersive AR Device [4] (b) Immersive AR (top) [3] and VR (bottom) Headsets [47] Figure 2: Immersive and Non-Immersive Devices. Non-Immersive Device -See digital content through a mobile screen. Immersive Device -View digital content through a headset.

Online learning had become a critical tool utilized by close to 70% of higher education institutions prior to the COVID-19 pandemic [19] . Instructors were already making use of virtual educational strategies such as asynchronous course delivery, synchronous online course delivery, or a flipped classroom model that utilizes both. It is valuable to understand these existing forms of online education and how they work before discussing specific challenges within each system and how AR or VR can help address these issues.

An asynchronous learning model involves students interacting with and responding to material at their own pace. Though students will still have to meet deadlines, the timing of when they learn/submit the material is flexible. An example of this model is a teacher posting all lecture material and class assignments with their respective deadlines at the beginning of a course. The students would then manage their time however they see fit in order to get these tasks done by the deadline. Asynchronous courses can use tools like video recordings of lectures, digitally distributed typed/written material, discussion posts, or a combination of these tools. This delivery method gives students flexibility in regards to when they access material, which can be crucial to academic success for non-traditional students navigating other time commitments like a job or taking care of their families [35] .

A synchronous model is what traditional face-to-face courses use, where students and their instructors meet regularly for teaching sessions, tests, and homework submissions. Synchronous online courses may require a different set of resources as compared to the asynchronous model. Learning Management Systems (LMSs) like Canvas or Blackboard have also been adopted by the majority of universities as supplementary resources intended to support teaching and learning activities [51] . Certain LMSs offer tools that allow for synchronous course delivery, like Blackboard's "Blackboard Collaborate" (formally Elluminate Live! [14] ). Universities have also adopted other third party options to conduct online classes such as video conferencing software, e.g. Zoom [5] . Tools commonly found within such platforms include video and text chat features, a participant list, polling/surveying tools, a raise hand tool, and the ability to record a session [6] . Synchronous courses can also make use of "screen-share" features that allow students to see what is on an instructor's computer screen, and these can be used in conjunction with digital content like PowerPoint slides to help relay course material.

A "flipped classroom" is a teaching model where "that which is traditionally done in class is now done at home, and that which is traditionally done as homework is now completed in class" [11] . This typically involves students viewing "lecture" material, or the material related to the introduction of concepts, at home as opposed to in the classroom. Class time is then spent on "more enriching activities" [56] that allow students to deeply explore concepts they learned from the lecture material. In an all-online environment, a flipped classroom could be implemented using asynchronous methods to distribute course material prior to synchronous sessions. The synchronous sessions would then focus on student application of knowledge learned from their material. This would involve the resources required of both asynchronous and synchronous teaching.

There are clear benefits in regards to existing distance learning education models, but several drawbacks have been noted as well. Distance learning in any form appears to decrease opportunities for social interaction and discourse as compared to traditional, inperson courses [19] . The current digital format has also been seen to disengage students from their courses due to technical issues or unsatisfactory experiences with the online class setting [45] . Schools that only offer online courses have also seen higher dropout rates than those which are in-person [60] .

These issues indicate that the way we currently deliver distance education could be damaging students' learning opportunities. However, they also give motivation for why we should work towards integrating AR and VR into distance education. The immersive nature and virtual components of AR and VR can create opportunities to address current drawbacks of distance education. We explore the different ways AR and VR address these issues throughout section 4.

Recent years have shown developments in the design of online coursework, and these advancements are worth understanding when considering how we can effectively make AR or VR useful for the classroom. Concepts like gamification have been applied to digital educational resources as a way to improve many aspects of the learning process. Using "game mechanics" like points, levels, challenges, or badges in educational activities has helped improved the ability to learn new skills by 40% compared to without the use of those mechanics [26] . Gamification has also led to increased commitment and motivation when participating in activities beyond just education [39] . Effective gamification requires the consideration of many aspects of a course like learning objectives or the characteristics of learners [39] , and successful implementation of gamification in a curriculum parallels many aspects of what "good" teaching already looks like [62] . Educational tools which make use of gamification are seeing great popularity as well. Duolingo, an phone app designed to help people learn languages through "gamified" lessons, had around 40 million monthly active users as of December 2020 [15] . Kahoot!, an online game where you can make your own quizzes on any topic of your choosing, reached 5 billion cumulative players around the world as of January 2021 [31] . Gamifying education has see great support as mentioned previously; learning to leverage gamification both in traditional distance learning models as well as when integrating immersive technologies into education could have a strong positive on educational systems if done correctly.

In this section we explore the specific issues faced by students utilizing current distance education methods. After describing the issue, we explore existing work in how AR and VR are being used to address the issue being faced. Finally, we consider what work remains to totally resolve the issue when using immersive technologies.

We will define social interaction as "an intentional event in which one person's behavior is directed toward another person or is in response to the other person's behavior" [25] . This definition remains the same both in "real-life" settings as well as online, though the interactions may appear differently between the two mediums (e.g. an example of social interaction in a digital setting may be a student sending a message via text chat to another student, while in real-life settings like in-person classrooms students will primarily directly talk to one-another). Virtual classrooms like Blackboard Collaborate are platforms which allow students to interact with the teacher or other students through text or voice chat, and these platforms can also enable students to see course material like slides remotely. Virtual classrooms and LMSs are different. An LMS provides features needed to handle the logistics of the entirety of a course, like the ability to post class-wide lesson materials, assessments, and feedback for everyone to see. Virtual classrooms attempt to replace the physical space of a classroom by focusing on creating opportunities for real-time interaction between users or users and content. Virtual classrooms can also differ from AR or VR learning modules in several ways. Existing virtual classrooms are designed to entirely replace the classroom for the duration of a whole course as opposed to being a substitute for single lessons which AR or VR learning modules may be specifically built for (e.g. the virtual classroom Blackboard Collaborate provides the tools needed for students and teachers to engage with each other as well as material during digital class periods, while a VR learning module for a course would have to be predefined to support the content related to a specific lesson). Existing non-VR or AR virtual classrooms are also typically web applications and only encourage as much social interaction as web-based voice/video platforms can. While distance learning methods give students more flexibility in accessing course content, studies have shown that students can feel "disconnected", or struggle to practice social interaction with others in these online environments [35, 45] . Traditional face-to-face education is shown to be "more likely to promote collaborative learning, student-faculty interaction, effective teaching practices, quality of interactions, and discussion with diverse others" when compared to a virtual classroom [19] . Quality social interactions have previously been claimed as a way for young children to develop cognitively [10, 16] , so the absence of these interaction can prevent this cognitive growth [17, 53] . This means students in current distance learning models are losing aspects of their education due to the lack of social engagement.

Since distance learning can decrease social interaction, research has used AR to facilitate social collaboration when users are separated. Attempts to use computer vision to recreate user movements into remote avatars have been under investigation for several years now [46, 55] . Raskar had previously shown that this could be done by using high depth cameras to capture a user's 3D image which could then be projected remotely for other users. However, since this method required camera images from multiple perspectives, it was not practical for the average learning environment. As a result, recent researchers have turned to other methods like generating avatars using low-cost cameras [46] or projecting 2D images to enhance collaboration [12] . For example, Michael et al. explored ways to cut costs for avatar generation using machine learning. He started by training two machine learning models on a dataset of 3D body scans. One of these models was trained to identify and extract the parts of the image which were the body, and the other was trained to then apply those extracted images onto a 3D model. After training both these models, a low-cost camera could be used to get full-body images of a person from multiple perspectives, and then the machine learning models could be fed these images to generate a 3D model. Michael et al. did use one other high-resolution scan of the face so that facial features were captured, but this was much more cost-effective than previous, similar approaches which used several high-end cameras to get the input images [46] . Billinghust et al. used HMDs and AR marker cards to project images of participants for video conferencing of physical cards [12] . The participants would wear the HMD and carry an AR marker card which projected their partner's video feed if seen through the HMD. The partners would then walk through and participate in an art sale. Billinghust compared the AR conferencing method to audio only conferencing and traditional video conferencing under the same context. In the AR conference, participants could move freely around the room with their cards and see their partner. In contrast, the traditional video conferencing took place over a desktop computer, while the audio conference was a phone call. Participants were then asked to rank their sense of presence as well as the conference's similarity to in-person meetings. Notably, the AR conference scored significantly higher (p value <.05) than audio or traditional video conferencing. However, the HMD obscured participants faces and field of view, and conversely made communication much harder during the AR conference.

Pejoska et al. used AR to aid social interaction while teaching construction workers [52] . They designed Social AR, which helped the workers communicate over large distances while on the job. Social AR allowed users to send voice and text messages through their mobile phone, as well as augment their video for others to view. For example, a user at one end of a construction site would be able to show their video feed in real time, annotate it, and the annotations would also appear to other users during creation. This allows workers to be able to see what their coworkers are seeing. Additionally, text features allow participants to discuss the annotations and video feed as if they were interacting in person. While this research is not used to teach construction, in indicates the potential of AR Study Device Result Raskar [55] Projectors and Surfaces Details theoretical "office of the future" that could connect collaborative spaces in different locations using projectors and wall surfaces Billinghurst [12] Head

Mounted Display AR conferencing can provide an increased sense of presence and improve transmission of communication cues for remote users Pejoska [52] Mobile Social AR successfully used to enhance video calls with overlaid drawings to increase social interaction during information sharing, as well as suggests methods for social interaction to be incorporated into distance learning via AR.

These studies indicate that AR can be used to provide a sense a presence with other classmates, which is crucial for distance learning, where students are not located in the same place. This makes AR a great avenue for enhancing distance education, as it enhances video calls and connects students collaboratively to bring social interaction in distance learning closer to that of traditional education.

The ability to socialize despite being physically separate is a critical aspect of the efficacy of virtual reality experiences. A primary reason VR is viewed as a unique alternative to common virtual communication tools like text or voice chat is due to its ability to emulate human interaction, which cannot be fully achieved over a video conference call (such as Zoom). Utilizing data from the National Survey of Student Engagement, Dumford and Miller analyzed first, fourth, and fifth year college students and found a significant correlation between online classes and social interaction [19] . These students had lower levels of collaborative learning, less student-faculty interactions, discussions, and lower quality of interactions [19] . VR can aid in this scenario because it will provide a simulation of face to face interaction, while still providing some of the convenience of online learning.

Socialization and interaction with VR appears to match in-person interaction experiences closely. In a study that focused on social interaction quality in VR, researchers examined how the reduced social information and behavioral channels in immersive virtual environments compared to that of the real world, and whether virtual reality environments as a whole were a viable alternative in terms of task completion and socialization [57] . Roth et al. [57] had participants interact in communicative scenarios (a negotiation) both through a virtual environment as well as a real world environment. After comparing the effectiveness in communication, socialization, and overall task completion across two different environments, one virtual reality-based and one in the real world, the researchers were able to confirm that "differences in effectiveness in the communicative role play were not present", and that the VR experience was equally as effective in enabling participants to adequately socialize and communicate while attempting to complete a task.

Studies in VR social interaction suggest that advanced computer graphics such as avatar facial expressions may not be necessary for VR communication. This can makes VR education applications more affordable and easier to adapt for educational institutions Study Device Result Roth [57] Head Mounted Display

Absence of cues like gaze or facial expression do not change effectiveness of communication in VR 

While current AR/VR research has developed additional opportunities for social interaction in distance learning, there are still limitations to the state-of-the-art. There are currently no standard metrics used for measuring social interaction in AR or VR, so the field would greatly benefit from establishing a standard to determine what AR/VR technologies and methods can best help in social interaction.

In terms of hardware, HMDs have a limited field of view, and obstruct the user's face. As a result, it is harder to make eye contact and experience a social connection when both users have a headset [12] . Future research into facial communication with HMDs (such as less obtrusive hardware, or another way to communicate non-verbally) can enhance social communication with AR/VR. In VR, more educational tools are becoming publicly available as well [50] . It could be valuable to evaluate these tools and how effective they are in both encouraging discourse as well as facilitating lessons. Understanding what makes these environments effective or ineffective could help us build better VR or AR educational platforms. This information could also help us see how to modify traditional distance learning education methods so that they are more effective in encouraging discourse.

Asynchronous and synchronous courses have both faced criticism in regards to how engaging they are for students. In asynchronous classrooms, students entirely lose the non-verbal communication present in face-to-face communication, which can damage students' sense of social presence and make it harder to stay engaged in a class [35] . In a study by McBrien et al. on how synchronous online courses affect student engagement, 9% of students in the study felt "disconnected" as a result of the digital course format. Similar to the previous section, one of the reasons for feeling "disconnected" is the minimal non-verbal communication available. Technical issues (i.e. poor internet connection or trouble with joining into a class) can have a huge detrimental effect on how "connected" students feel with a course, as well. The negative responses from students in the study by McBrien et al. included comments like "sometimes it was hard to keep up with the messages, listening to commentators, and reading over the lessons," "lack of visual stimulation during lecture," "frustration signing on and getting kicked off," and "microphone troubles." It seems like certain students would have preferred to have fewer stimuli going on during courses. Conversely, there was a claim that there was too little visual stimulation, indicating that the material being focused on by the teacher may have been too bland given the online setting. The last couple of claims indicate the significance of technical issues in the educational experience; any trouble with getting the class to work as it is expected to seems to greatly take away from the learning experience. John Keller's ARCS model for motivation claims that motivation stems from four major components: attention, relevance, confidence, and satisfaction [36] . Looking at the students' claims from the perspective of Keller's ARCS model, it seems like the different issues behind the complaints could have made it harder for students to maintain uninterrupted attention or feel satisfied with the online course. Decreased satisfaction or attention has a negative effect on a person's motivation according to Keller, and decreased motivation may have damaged students' abilities to engage with the class.

Researchers have already turned to AR to investigate its effect on engagement and focus. Ferrer-Torregrosa et al. utilized AR to teach anatomy students in a flipped classroom distance learning model [23] . Participants were given AR books, traditional notes with pictures, and videos to learn anatomy content. They were then assessed by which tool (book, notes, or video) kept the students more engaged and focused. Notably, the AR books were the superior method for holding a student's attention and focus without the teacher present. Mahadzir et al. took AR motivation research a step further by designing AR books specifically to try to increase motivation in English language learning [43] . Using the Keller model for motivational design [36] , Mahadzir et al. created AR books for primary students in Malaysia that do not require teacher assistance using the ARCS evaluation of motivation. All students were considered engaged and had a motivated interest in using the AR books, determined both by observation and first person interviews. While the study had very few participants (n=5), it represents the potential for AR to increase student participation in remote learning environments.

Additionally, consumer mobile augmented reality applications have been assessed for their usage in increasing student motivation. Anatomy 4D, which is meant to supplement anatomy learning, is a free mobile AR application for teaching students anatomy. The software shows a 3D human body, with annotations labeling the different body parts. This software can be downloaded and used without a teacher present, and offers a great example of AR remote learning tools. Through pre-usage and post-usage tests, Khan et al. determined a significant increase in student motivation from using Anatomy 4D [38] . These studies show that AR had a significant increase in student engagement and focus. As engagement is a major difficulty in distance education, AR can be used to benefit distance education by increasing engagement.

Result Mahadzir [43] Desktop AR engaged student interest and retained it during the experience Khan [38] Mobile Motivation and attention was increased by 14% and 31% respectively 

The advantages of using VR to teach educational objectives and improve student engagement are similar in many ways to the advantages of using a computer or interactive simulation, particularly a 3D computer simulation. Computer simulations create a sense of immersion by walking a user through the experience from a first-person perspective, such as a virtual tour of a historic building. Computer-based simulations have been used for many years in computer-assisted instruction (CAI). Steinberg asserts that "simulations make it possible to explore new domains, make predictions, design experiments, and interpret results" [61] . VR also gives the user a first person perspective of the experience; however, instead of interacting with the experience via a keyboard and mouse, the user can physically move around and utilize their hands to create a greater sense of immersion. As a result, VR maintains many of the same qualities and advantages of computer simulations listed above Through these studies, virtual reality experiences have provided a unique ability to improve user engagement and focus due to the novelty of the interaction device and unique characteristics of the experience.

VR or AR has already proven to be an engaging supplemental resource for different subjects whenever available. There have also been reports that VR learning environments have shown an increase in positive emotions along with a decrease in negative emotion compared to both video and textbook options [7] . Going back to the study by McBrien et al., one of the issues mentioned was the lack of visual stimuli in the traditional online learning environment. Both AR and VR do a phenomenal job in creating engaging, informative environments, which should resolve this issue. However, another similar noteworthy comment made was the potential for too much stimuli in these virtual environments. VR or AR could easily involve more stimuli that the traditional distance education methods, so this seems like a factor to watch out for. Understanding when there is too much going on at once in existing distance education platforms could provide a basic idea of what a focused, effective teaching environment might look like in VR or AR. Research into what factors add to the educational value of a distance learning environment and which factors are excessive will help with removing unnecessary stimuli in these environments. That information could then be considered when designing VR or AR educational environments.

Schools that rely entirely on distance learning have previously held higher dropout rates than those which are in-person, but these statistics have also been tied to ineffective online teaching practices [60] . Simpson writes that "institutions have focused too much on the provision of teaching materials, especially online, and too little on motivating students to learn." Using VR in education has led to improved knowledge acquisition and understanding of material compared to those learning via video, and students learning via VR have shown better performance remembering than those learning via textbook or video. AR technology has also been demonstrated to increase knowledge acquisition rate among a variety of educational subjects [72] . AR has also made abstract or complex concepts easier for students to visualize and understand. For example, AR could allow a learner to visualize phenomena like airflow or magnetic fields using virtual 3D objects [68] . Using immersive technology to illustrate these typically unobservable phenomena would give students a novel opportunity to understand new concepts within a familiar context.

AR technology has been demonstrated to increase knowledge acquisition rate among a variety of educational subjects [72] due to AR's ability to help visualize abstract and 3D objects. This is especially helpful for mechanical psycho-motor tasks, as AR overlays can show intuitive instructions for user activity without switching to an external screen. This was demonstrated with HMDs in Henderson et. al. by using AR displays to facilitate assembly alignment [32] . Henderson tested the time and accuracy for users to determine the location of parts, position them, and then align the parts together correctly. Participants aligned the mechanical parts almost twice as fast as compared to a traditional screen, with about 50% more accuracy. Additionally, subsequent studies showed an AR instruction to be almost equivalent to labeling each and every assembly part. However, since it can be unrealistic to try label every part, AR applications can be used as a valid learning substitute. Non-immersive devices have also assisted in education when a teacher cannot be physcally present. Schoop et al. used AR to teach construction for do-it-yourself projects [58] . Common household tools were converted to help with allignment, drilling holes, measuring wood, and etching details. The enhanced dynamic feedback demonstrated the ability for AR to work as an assisted teacher, as laypeople were able to use skilled machine tools and accomplish traditionally skilled machining tasks. AR has also been researched in the academic teaching realm. In addition to studying motivation, Ferrer-Torregosa et al. analyzed how AR can increase students' abilities to self-learn, as well as their information comprehension [23] . When compared to traditional notes and videos, students felt more comfortable performing learning activities outside of class and increased their comprehension of the specified material after learning via AR. Ferrer-Torregosa et al. did not perform pre-and post-tests in order to confirm students increased comprehension of the material, but the students' perceived increases in comprehension (from metacognative survey analysis) can contribute to their actual understanding of material.

To increase information retention, Duesner et al. included haptics in their study of AR books [18] . Using a handheld device, participants were given books that introduced magnetism and electromagnetism through traditional or AR formats. All participants studied their respective materials for the same amount of time. Through pre-tests, post-tests, and retention tests (four weeks after the study), participants were evaluated both on their memory recall and comprehension of the physics concepts. The participants using the AR interactive book scored slightly higher in the post-test, especially for questions that required visualization (such as the left hand rule or drawing magnetic lines). However, both groups performed approximately the same in the retention test.

AR can also increase information retention by supplementing distance education. Küçük et al. created a mobile AR app to provide extra instruction for anatomy students in addition to lectures [41] . With the app, students could scan images of anatomy body parts and then view 3D animations and sounds to assist in learning. Students were able to retain more information using the AR mobile application while also facing a lesser cognitive load than with traditional studying. This represents AR's ability to aid in the difficulties of learning through distance education without interrupting the traditional distance education format. These studies indicate that AR can help students learn better, as well as more quickly compared to traditional methods. This makes AR a prime candidate for education, especially in distance education, where time with a teacher is significantly reduced.

Device Result Henderson [32] Head Mounted Display

Schoop [38] AR enhanced tools

Validation of AR to assist with learning in construction tasks Ferrer-Torregosa [23] Handheld Display

Students learning with AR scored significantly higher compared to video or traditional learning Duesner [18] Handheld Device Students with AR scored higher than students learning with traditional books Küçük [41] Mobile Students retained more information with less cognitive load 

VR learning environments consistently show benefits in areas such as comprehension, memory, and information retention. A study at the University of Warwick in 2018 observed such improvements. Study participants who learned in VR settings demonstrated improved knowledge acquisition and understanding of material compared to those learning via video, and showed better performance in terms of information recollection than those learning via textbook or video. Additionally, participants reported a heightened sense of novelty and interest toward the VR learning medium as a whole, along with a decrease in negative emotion compared to both video and textbookbased options for instruction [7] . This indicates that VR can be helpful for improving comprehension of information compared to traditional learning techniques such as textbooks and videos. Another major advantage of using virtual reality to achieve learning objectives is that it is highly motivating. Even before VR became more mainstream, studies with computer based immersive experiences generated positive attitudes towards learning [48] . Mikropoulos et. al. created a VR application where future teachers could explore a lake and learn about different sea organisms. After using the application, all of the participants felt the experiences could help in a teaching environment. Furthermore, VR presents novel opportunities to not only improve overall information retention and engagement, but provide opportunities for learning that cannot be achieved in person. For example, VR is capable of emulating field trips in ways impossible for both distance education as well as in person. In 2019, a field trip-like study by the Pennsylvania State University was used to test information retained while in the field. There were 3 groups: a "normal" field trip in person, a basic virtual field trip, and an enhanced virtual field trip. Those in the basic virtual field trip were provided a 10 by 10 area using an HTC Vive HMD, which is a VR HMD. Those in the enhanced virtual field trip used the same setup, and were also provided the option to view locations at an elevated level (27 feet high). Those in the basic virtual field trip reported higher mean levels of enjoyment with the field trip, and those in the enhanced field trip performed better than the actual field trip. All students then undertook the trip from 35-45 minutes. A Spatial Situation Model (SSM) is "a mental representation that comes into play when users attempt to retrieve spatial information from memory. [73] ." Given a questionnaire in the style of an SSM, those in the basic virtual field trip performed better than those in the actual field trip, and the enhanced virtual reality performed better than both. This shows that VR can not only emulate a classroom, but can provide educational experiences which could not be provided by an in-person classroom alone. [73] . [73] .

While the results of VR studies are not as significant in comprehension and retention as AR studies, they do help with information recollection, due to the enhance realism and visualization VR provides. For this reason, it can be useful in education.

Result Allcoat [7] Head Mounted Display Improved recollection and engagement Mikropoulos [48] Head Mounted Display VR seen as valuable educational tool 

Within augmented reality, not much research has been conducted on information retention for distance learning. While Duenser et al. did test retention for physics education, there were not enough participants to determine conclusively AR's effect on retention [18] . One concern voiced by students in the same study by McBrien et al. mentioned in section 3.2 was, "Sometimes it was hard to keep up with the messages, listening to commentators, and reading the lesson," [45] indicating that too much stimuli could harm students' learning experiences. Doing more research on how different amounts of visual stimuli in an AR or VR experience affect information comprehension would give us a better idea of how to design lessons using VR or AR.

As mentioned previously, education AR or VR resources were far too rigid to be utilized by teachers without a lot of coding experience in the past. Many studies have explored the viability of using AR and VR for educational purposes, but these studies used pre-developed content for instructors. Developing content requires advanced skills in both AR and VR technology [41] , and is typically created by individuals far removed from the educational subject matter, such as a contracted developer. This makes it very difficult for instructors to customize content for students, as well as adapt and change lesson plans as fluidly as with traditional learning materials [37] . This issue almost entirely prevents teachers from adopting AR or VR resources in education, as this stops educators from designing virtual learning environments that are specific to their material.

There has been a large push within AR research to facilitate the creation of AR development resources for teachers and laypeople without coding experience. Using the Equator Component Toolkit, a system used to integrate digital devices [20] , Hampshire et al. was able to create an AR developer application [30] . It features a drag and drop user interface, where developers can use AR content pre-created for general applications. While this has not yet been used in an educational context, it demonstrates the desire for AR creation software, as well as the need for user-specific development tools [30] . Additionally, Hampshire's group created ComposeAR [59] . ComposeAR requires python for added functionality such as interaction or application plugins, but implements a graphic user interface to compile and view code as it is being created. Specifically for distance education, Ying Li created AR Environment for Remote Education (ARERE) [70] . Students are able to see and interact with the same virtual object from different locations using this tool. Additionally, the digital objects track physical objects that are distributed to students in advance, so they can tangibly interact with the physical object and observe as it changes digitally.

This has not yet been tested on students for feasibility in an actual education environment, but it represent promising potential for AR to give a sense of presence for remote education. While digital overlays can be extremely useful, it is sometimes necessary for students to be able to physically touch and interact with their learning resources. To provide haptic feedback, instruction materials have utilized real objects with AR markers -easily recognizable 2D symbols such as pictures to designate where to display AR objects -for augmentation through computer vision tracking techniques. This allows students to physically rotate and discover the augmented object, adding sensory feedback to the educational experience [24] . In this way, the same mechanical hardware can be used for a variety of teaching levels, reducing hardware cost and increasing content variability. These technologies can greatly aid understanding in areas such as biology, astronomy, mechanics, and other fields where digital overlays can be used to help describe typically unobservable physical structures. Additionally, commercial HMDs such as the HoloLens allow users to interact with digital overlays by touching digital buttons [69] . This, combined with physical objects, can allow for haptic and digital feedback, further aiding the learning process.

Many commercial AR tools also exist to aid instructors in education. Wondershare offers interactive AR mobile storybooks for children to creatively learn literacy while [67] . It features traditional story books such as Little Red Riding Hood, and teaches children how to read. As they read the words, they can watch Little Red Riding Hood perform the actions. ARTutor allows teachers to quickly and easily augment textbooks with AR content [42] . Teachers can upload a book pdf and add 2D overlays, sound, and videos for students. Then, as students read the physical book through the ARTutor smartphone application, they will be able to view the augmented content. As teachers can easily upload any sound, video, or image files, ARTutor provides immense customizability for teachers. Teachers can add audio of themselves explaining a formula in a textbook or a video of a particular battle in a history book. Quiver is another commercially available software that allows users to download educational coloring pages in order to teach students about science and mathematics [54] . The coloring page will then become a 3D image, allowing the student to see their creation come to life by adding a new dimension as well as animations. As the content is not customizable, this application is more suitable for simple subjects with younger children.

While many studies have explored the viability of using VR for educational purposes, these studies generally used pre-developed content for instructors. Developing content requires advanced skills in VR technology [41] , and is typically created by individual far removed from the educational subject matter, such as a contracted Figure 8 : Demonstration of QuiverEducation for learning about volcanoes. Students color image of a volcano (left) and watch it erupt through the Quiver smartphone app (right). [54] developer. This makes it very difficult for instructors to customize content for students, as well as adapt and change lessons plans as fluidly as with traditional learning materials [37] . For this reason, further research into content creation and the ability to customize content for instructors would be helpful in advancing VR educational applications, especially for distance learning. This can include software that allows for creating customized content without intense coding knowledge, as well as dynamic programs, where the teacher can easily adapt current content into a VR learning environment. For distance learning, this could be environments where the teacher can teach normally, and the students will simply experience the content in an immersive way. Youngblut conducted an extensive survey of research and educational uses of virtual reality during the 1990s, and attempted to answer questions about the use and effectiveness of virtual reality in kindergarten through grade 12 education [71] . They found that there are unique capabilities of virtual reality, and the majority of uses included aspects of constructivist learning, which is a theory that that recognizes the learners' understanding and knowledge based on their own experiences prior to entering school. He generally concluded that VR holds potential educational effectiveness for special needs students [71] . However, he also made note of the contexts in which VR is not a suitable option for educational use, and where its downsides are most prevalent, noting that the chief inhibitor of widespread implementation is the lack of customizable content: teachers commonly reported frustration with the lack of ability to customize educational content for a lesson, both before and during the lesson.

More and more AR/VR resources are becoming available to the public, but one of the greatest challenges faced when trying to adopt VR or AR as an educational resource is the inability to easily create virtual environments without programming knowledge. VR and AR are advancing rapidly, so a survey of what resources are currently available, their strengths and weaknesses, and what is needed for them to be ideal for education could be valuable in trying to understand how these platforms can be made more accessible for education. Updated research on how effective new AR/VR educational resources are would give us a direction in how to move forward with developing an AR or VR content creation platform for educators. In order to consider AR or VR as a viable option for any form of education, teachers will need to be able to easily manipulate the virtual environments so that they can work with curricula or lesson plans.

AR and VR have proven to be valuable educational resources where they fit in, but we have found several issues that need to be overcome in order to make these technologies more widely available to educators. Critiques of traditional distance education include the decreased amount of social interaction, lack of discourse, and absence of non-verbal cues within these environments [19, 35, 45] . VR and AR help patch these issues, as they encourage communication more effectively that traditional audio or video methods. However, they could still benefit from further advancements. AR HMD's were in the way when two users were trying to communicate and make eye contact [12] , so research in how communication is affected with varying types of HMD's would be valuable. VR can effectively facilitate opportunities to socialize, but understanding how well VR encourages discourse in education environments or how successful existing VR educational environments are in supporting discourse is still an area that should be explored. In terms of engagement and focus, more research is needed in determining what amount of visual stimuli helps to engage and focus students without being too distracting. Distance learning environments have faced criticism for causing disengagement between students and their courses for reasons like technical issues or improper amounts of visual stimulation related to the lesson [45] . Traditional distance educational environments and VR or AR environments will have different requirements of users, and these will likely act as a limitation for widespread adoption of AR and VR. Those limitations will be discussed further in sections 4.1.3, 4.2.3, 4.3.3, 5.0.3, and 6. Other factors that negatively impacted student engagement in traditional distance learning environments were related to having too much or too little stimuli during the lesson. AR and VR are capable of creating extremely engaging environments due to their immersive nature, so virtual lessons should be engaging for students. Too much stimuli could become an issue in these environments, though. Understanding what factors are necessary (or unnecessary) for students to have in traditional distance education might give us an idea of how we should be designing virtual environments for students. Additionally, more research is still needed how virtual lessons affect long-term information retention.

Acceptance of AR or VR technology by teachers or educational systems will also play a role in the widespread adoption of AR or VR in education. Teachers have concerns about the need for continuous training required to be able to use the devices effectively, and opinions about the process of 3D modeling received both positive and negative feedback [63] . Further research in how educators under different age groups feel about immersive technologies may also be valuable in better understanding what teachers think about bringing AR and VR into their classrooms. Studies aimed at trying to gauge teachers' willingness to accept technologies like AR and VR into the classroom do exist, but focus on teachers which are millennials or younger [21, 44] . During the 2017-2018 school year, at least 75% of teachers in the United States were 30 years or older, and about a quarter of teachers in the U.S. were over 50 years old [1] . By only studying younger teachers, we are missing out on how a substantial portion of the education workforce might see the adoption of VR or AR into education.

Financial concerns about bringing these devices into the classroom are also important constraints to consider when deciding if AR or VR can be widely used in schools. Immersive devices have gotten cheaper, and devices like Google Cardboard exist now as well. However, robust HMDs may still prove to be challenging to fit into school budgets. Higher-end AR devices like the Microsoft Hololens 2 are also still too expensive to enter the consumer market (the Hololens 2 retails at $3500 USD on the Microsoft Store). Educational systems commonly face funding issues, so more research with regards to whether schools can afford immersive technologies is necessary.

The last major challenge preventing educators from adopting VR or AR into their classrooms is the inflexibility of the technology when it comes to designing lessons. Teachers need to be able to easily create virtual environments related to their curricula without programming knowledge. There have been recent advancements in what resources are available as educational VR or AR tools, so research into what resources are available now, as well as how effective these resources are would be valuable. While investigation into content creation in AR and VR has been attempted, there is still room for future research. Current methods are either not customizable, or require much time and practice to create. While ARTutor is easy to use and customizable, it only provides 2D content, and therefore does not take advantage of AR's immersive 3D potential. Work in creating platforms which allow users to create thorough virtual experiences easily would be extremely valuable in pushing VR and AR into education.

A crucially research direction for the future is to establish metrics for evaluating immersive environments in education. The methods utilized in this paper were more categorical, and could not numerically quantify what methods for AR and VR are best. Having a universal metric for future researchers to follow will help in evaluating these technologies.

AR and VR hardware are integral to providing an immersive experience for users. Current AR headsets include the HoloLens and digital overlay glasses. However, due to the high cost of the HoloLens and technical limitation of AR glasses, VR headsets with cameras have also been used to create AR experiences. These headsets, along with the HoloLens, are relatively large and quite heavy. This can be uncomfortable, especially for younger students. Further research into increasing computing power or decreasing headset size would be helpful in enhancing the user experience for AR and VR technology.

Currently, certain technological aspects of AR and VR hinder their educational advancement. For classrooms, AR and VR technology must become more user friendly from a teacher's perspective [37] , so that they can teach and present the AR/VR content with similar effort as teaching in traditional methods. This could include developing a more user friendly teaching interface, or automating some of the AR/VR content so the teacher can focus on instruction.

Alternate forms of input are also helpful [33] . While this has of course been implemented through controllers for VR HMDs and HoloLens, mobile VR and most AR applications do not utilize hand tracking for interaction. Alternate forms of input increase the interactablility of displays, further engaging students. The HoloLens has the ability for hand and eye tracking [40] and touch interaction [69] , and mobile devices can utilize hand tracking to incorporate touch feedback. However, these have not yet been realized or evaluated in an educational context. Utilizing the sense of touch will be very helpful to increase interactivity and engage kinetic learners.

Furthermore, educational solutions that leverage AR and VR technologies as a whole must evolve, both in terms of technical feasibility and in acceptance by educators. Like many educational innovations in the past, the use of AR in classrooms could encounter constraints from schools and resistance among teachers. The learning activities associated with AR and VR usually involve innovative approaches such as participatory simulations and studio-based pedagogy [37] . The nature of these instructional approaches however is quite different from the teacher-centered, delivery-based focus in conventional teaching methods, where the teacher is the focal point of the student body and student participation is less frequent. Institutional constraints such as covering a certain amount of content within a given time frame also cause difficulties in implementing novel educational initiatives like this [37] . Thus, there may be a gap between the teaching and learning methods currently used in classrooms and the student-centered and exploratory nature of learning engendered by AR and VR systems. Designers of AR and VR learning environments need to be aware of this gap and provide support to help teachers and students bridge it, ideally in the form of tutorials, listening sessions, and working closely with educators in order to ensure the technology is suitable for the unique challenges education presents.

VR and AR do have technical demands that may be impractical for the average present-day classroom. We have seen traditional synchronous distance education courses run into connectivity issues in the university setting where the number of users are large. AR or VR educational settings should make internet connection requirements more demanding than video conferencing software due to the additional data needed for the virtual environments. This means that students will likely need much stronger internet connections to run these devices without interruption, and running a university-like VR lecture hall with over a hundred students might be impossible at the moment because of the internet bandwidth required. However, the development of 5G connection technology could make this possible. 5G promises internet speeds of greater than one gigabit per second [65] , which would make streaming large amounts of data much more feasible. Drawbacks to 5G, like possible issues with wall-penetration do exist, but the bandwidth offered by 5G connectivity should expand on online capabilities for AR or VR.

AR/VR allow digital images to interact in our real world, making them useful in education, particularly within distance education, where a teacher cannot always be present with a student. AR and VR have been shown to increase social interaction, comprehension, and engagement. However, multiple hindrances such as technology and hardware limitations as well as cost impede its adoption in education institutions. While studies suggest AR and VR can be most beneficial in K-12 education, where interaction, engagement, and focus play a larger role in the learning process, both the cost of hardware, educator adoptions, and developing content for such a wide variety of curriculum reduce the practicality of adoption within K-12 schools. Currently, it seems as if both AR and VR will be great for specific, and general educational knowledge to supplement teacher instruction, similar to educational activities or field trips. They cannot cover everything a student must learn, but they can help to reinforce knowledge and keep students engaged.

In this paper, we first assessed the educational challenges presented by distance learning as a whole, and then identified 4 main challenges that distance learning currently presents as compared to inperson instruction: the lack of social interaction, reduced student engagement and focus, reduced comprehension and information retention, and the lack of flexible and customizable instructor resources. After assessing each of these challenges in-depth, we examined how AR/VR technologies might serve to address each challenge along with their current shortcomings, and finally outlined the further research that is required to fully understand the potential of AR/VR technologies as they apply to distance learning.

AR and VR are prime candidates for addressing the various educational challenges presented by distance learning, especially during the COVID-19 pandemic, but we find they are currently inadequate for widespread adoption in the educational community and require further technological developments to take place. The COVID-19 pandemic has heightened the need for interactive and engaging educational environments, as the forced transition to distance learning has resulted in instruction being generally limited to discussions and lectures presented via video conferencing tools such as Zoom. This widespread implementation of distance learning has led to decreased student motivation and information retention, primarily due to the fact most students are unfamiliar with the format of distance learning and the instruction styles are often less engaging than if the content was delivered in-person.

At first glance, and especially in terms of individual features, AR and VR educational solutions appear to be ideal choices to help combat these challenges with student motivation, engagement, and information retention. Due to the fact they closely mimic learning in-person through a 3-dimensional environment, the use of AR and VR technologies as educational tools has been demonstrated to improve knowledge acquisition among a variety of educational subjects. Furthermore, AR and VR have also been shown to improve student engagement and motivation in the classroom, as immersive lectures are much more interesting and comprehensive than lectures presented on a 2-dimensional screen. AR and VR educational solutions were already being used before the pandemic for these reasons, in contexts such as supplementing in-person instruction through an AR-based anatomy lesson.

Despite presenting numerous advantages over both in-person instruction and distance learning, AR and VR educational solutions are still not technically mature enough yet to be implemented in a widespread fashion as a direct solution to many of the challenges presented by distance learning. In this paper, we note how a chief inhibitor of widespread adoption by the educational community is the lack of customizable content: teachers commonly reported frustration with the lack of ability to customize educational content for a lesson, both before and during the lesson. Additionally, further research to reduce motion sickness and eye strain for AR and VR is necessary before incorporating these devices into a required curriculum, as students must feel comfortable learning for long periods of time without fear of negatively impacting their health. Finally, the cost of high-end versions of AR and VR devices is also a major inhibitor of their widespread use: educators must be able to buy these devices in bulk for affordable prices. Additionally, further applied research can help educators and institutions realize the full potential of AR and VR for a variety of subjects. We hope that this paper brings to light these limitations and aids researchers in assessing the current state of immersive technologies as educational resources. We suggest areas of improvement to promote adoption of AR and VR in educational environments for distance learning, with the goal that AR and VR may soon be able to supplement or even completely replace the entire in-person classroom experience.

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