Virtual Reality and Assistive Technologies: A Survey <s> Visual-feedback-based VEs for mobility impairments <s> Virtual reality (VR) has finally come of age for serious applications in the behavioral neurosciences. After capturing the public imagination a decade ago, enthusiasm for VR flagged due to hardware limitations, an absent commercial market and manufacturers who dropped the mass-market products that normally drive technological development. Recently, however, improvements in computer speed, quality of head-mounted displays and wide-area tracking systems have made VR attractive for both research and real-world applications in neuroscience, cognitive science and psychology. New and exciting applications for VR have emerged in research, training, rehabilitation, teleoperation, virtual archeology and tele-immersion. <s> BIB001 </s> Virtual Reality and Assistive Technologies: A Survey <s> Visual-feedback-based VEs for mobility impairments <s> The purpose of this paper is to present an overview of the adaptations that have been done to VividGroup's Gesture Xtreme projected VR scenarios in order to facilitate their use in neurological rehabilitation. First, the scenarios and the adaptation (control of the type, speed, location and direction of all stimuli) are briefly described. The advantages and limitations of the adapted VR system as a rehabilitation tool are presented. Next, initial results and two examples of case studies, one a patient following stroke and one who requires balance training as a result of complete spinal cord injury, are used to illustrate applications of this VR system to rehabilitation. Copyright © 2003 John Wiley & Sons, Ltd. <s> BIB002 </s> Virtual Reality and Assistive Technologies: A Survey <s> Visual-feedback-based VEs for mobility impairments <s> This paper presents preliminary data from two clinical trials currently underway using flat screen virtual reality (VR) technology for physical rehabilitation. In the first study, we are comparing a VR-delivered exercise program to a conventional exercise program for the rehabilitation of shoulder joint range-of-motion in patients with chronic frozen shoulder. In the second study, we are comparing two exercise programs, VR and conventional, for balance retraining in subjects post-traumatic brain injury. Effective VR-based rehabilitation that is easily adapted for individuals to use both in inpatient, outpatient and home-based care could be used as a supplement or alternative to conventional therapy. If this new treatment approach is found to be effective, it could provide a way to encourage exercise and treatment compliance, provide safe and motivating therapy and could lead to the ability to provide exercises to clients in distant locations through telehealth applications of VR treatment. VR is a new tec... <s> BIB003 </s> Virtual Reality and Assistive Technologies: A Survey <s> Visual-feedback-based VEs for mobility impairments <s> We present a wireless virtual reality system and a prototype full body Tai Chi training application. Our primary contribution is the creation of a virtual reality system that tracks the full body in a working volume of 4 meters by 5 meters by 2.3 meters high to produce an animated representation of the user with 42 degrees of freedom. This - combined with a lightweight (<3 pounds) belt-worn video receiver and head-mounted display - provides a wide area, untethered virtual environment that allows exploration of new application areas. Our secondary contribution is our attempt to show that user interface techniques made possible by such a system can improve training for a full body motor task. We tested several immersive techniques, such as providing multiple copies of a teacher's body positioned around the student and allowing the student to superimpose his body directly over the virtual teacher None of these techniques proved significantly better than mimicking traditional Tai Chi instruction, where we provided one virtual teacher directly in front of the student. We consider the implications of these findings for future motion training tasks. <s> BIB004 </s> Virtual Reality and Assistive Technologies: A Survey <s> Visual-feedback-based VEs for mobility impairments <s> The objective of this study was to provide experimental data to support a proposed model of VRbased intervention. More specifically our goal was to examine the relationships between cognitive and motor ability and performance within virtual environments. Thirteen participants who have had a stroke participated in the study. They each experienced three virtual environments (Birds & Balls, Soccer and Snowboard) delivered by the GX- video capture system. After each environment they complete a scenario specific questionnaire and Borg’s scale for perceived exertion. Their cognitive, motor and sensory abilities were measured as well. The participants’ responses to the VR environments showed that they enjoyed the experience and felt high levels of presence. The results also revealed some moderate relationships between several cognitive abilities and VR performance. In contrast, the motor abilities and VR performance were inversely correlated. In addition, there was a relationship between presence and performance within the Soccer environment. Although these results support some components of the proposed model it appears that the dynamic nature of the virtual experiences would be more suited to comparisons with different measures of motor ability than those used in the current study. <s> BIB005 </s> Virtual Reality and Assistive Technologies: A Survey <s> Visual-feedback-based VEs for mobility impairments <s> This survey paper addresses some issues related to the application of computer vision techniques to improve the welfare of people with special needs. The main problems and current work on topics like sign language processing and wheelchair control will be presented. The paper also introduces an ongoing project that aims at creating a free software environment that will include implementations of a large amount of computer vision, pattern recognition and machine learning techniques, tuned to the problems related to the digital inclusion of people with special needs. The software will also serve as an experimental environment, where new techniques will be implemented, tested and compared <s> BIB006 </s> Virtual Reality and Assistive Technologies: A Survey <s> Visual-feedback-based VEs for mobility impairments <s> Previous research has shown that computer-based tasks can motivate people with autism and encourage learning. As a computer-based medium, Virtual Environments (VEs) offer a potentially useful tool for social skills training for people with autistic spectrum disorders (ASDs). However, there are some concerns over whether people with ASDs can understand, use and interpret the technology appropriately. This paper adopts a qualitative case-study approach to report observations of, and comments from, two adolescent boys with ASDs, gathered during a series of sessions using a virtual cafe and bus environment. Although there were signs of repetitive behaviours, literal interpretation of the scenes, and that the VEs were treated as not having real-world relevance, these were not the dominant modes of responding. Instead, participants seemed to interpret the scenes meaningfully and appreciated the opportunities to discuss appropriate social responses with a facilitator sitting alongside. They enjoyed using the VEs and provided specific examples of how the VEs had helped, or could help, them in the real world. This gives encouraging support for the idea that VEs can be used and interpreted meaningfully by at least some students with ASDs. The paper concludes with some considerations for the future development of VEs for members of this population. <s> BIB007 </s> Virtual Reality and Assistive Technologies: A Survey <s> Visual-feedback-based VEs for mobility impairments <s> AIM ::: To evaluate the effects of ''Playstation EyeToy Games'' on upper extremity motor recovery and upper extremity-related motor functioning of patients with subacute stroke. ::: ::: ::: METHODS ::: The authors designed a randomized, controlled, assessor-blinded, 4-week trial, with follow-up at 3 months. A total of 20 hemiparetic inpatients (mean age 61.1 years), all within 12 months post-stroke, received 30 minutes of treatment with ''Playstation EyeToy Games'' per day, consisting of flexion and extension of the paretic shoulder, elbow and wrist as well as abduction of the paretic shoulder or placebo therapy (watching the games for the same duration without physical involvement into the games) in addition to conventional program, 5 days a week, 2-5 hours/day for 4 weeks. Brunnstrom's staging and self-care sub-items of the functional independence measure (FIM) were performed at 0 month (baseline), 4 weeks (post-treatment), and 3 months (follow-up) after the treatment. ::: ::: ::: RESULTS ::: The mean change score (95% confidence interval) of the FIM self-care score (5.5 [2.9-8.0] vs 1.8 [0.1-3.7], P=0.018) showed significantly more improvement in the EyeToy group compared to the control group. No significant differences were found between the groups for the Brunnstrom stages for hand and upper extremity. ::: ::: ::: CONCLUSION ::: ''Playstation EyeToy Games'' combined with a conventional stroke rehabilitation program have a potential to enhance upper extremity-related motor functioning in subacute stroke patients. <s> BIB008 </s> Virtual Reality and Assistive Technologies: A Survey <s> Visual-feedback-based VEs for mobility impairments <s> BACKGROUND AND PURPOSE ::: The purpose of this retrospective and prospective case report is to describe the feasibility and outcomes of using a low-cost, commercially available gaming system (Wii) to augment the rehabilitation of an adolescent with cerebral palsy. ::: ::: ::: PATIENT AND SETTING ::: The patient was an adolescent with spastic diplegic cerebral palsy classified as GMFCS level III who was treated during a summer session in a school-based setting. ::: ::: ::: INTERVENTION ::: The patient participated in 11 training sessions, 2 of which included other players. Sessions were between 60 and 90 minutes in duration. Training was performed using the Wii sports games software, including boxing, tennis, bowling, and golf. He trained in both standing and sitting positions. ::: ::: ::: OUTCOMES ::: Three main outcome measures were used: (1) visual-perceptual processing, using a motor-free perceptual test (Test of Visual Perceptual Skills, third edition); (2) postural control, using weight distribution and sway measures; and (3) functional mobility, using gait distance. Improvements in visual-perceptual processing, postural control, and functional mobility were measured after training. ::: ::: ::: DISCUSSION AND CONCLUSION ::: The feasibility of using the system in the school-based setting during the summer session was supported. For this patient whose rehabilitation was augmented with the Wii, there were positive outcomes at the impairment and functional levels. Multiple hypotheses were proposed for the findings that may be the springboard for additional research. To the authors' knowledge, this is the first published report on using this particular low-cost, commercially available gaming technology for rehabilitation of a person with cerebral palsy. <s> BIB009 </s> Virtual Reality and Assistive Technologies: A Survey <s> Visual-feedback-based VEs for mobility impairments <s> Difficulties in understanding symbolism have been documented as characteristic of autistic spectrum disorders (ASDs). In general, virtual reality (VR) environments offer a set of potential advantages for educational intervention in ASD. In particular, VR offers the advantage, for teaching pretend play and for understanding imagination, of it being possible to show these imaginary transformations explicitly. This article reports two case studies of children with autism (aged 8:6 and 15:7, both male), examining the effectiveness of using a VR tool specifically designed to work on teaching understanding of pretend play. The results, confirmed by independent observers, showed a significant advance in pretend play abilities after the intervention period in both participants, and a high degree of generalization of the acquired teaching in one of them. <s> BIB010 </s> Virtual Reality and Assistive Technologies: A Survey <s> Visual-feedback-based VEs for mobility impairments <s> BackgroundStroke is a frequent cause of adult disability that can lead to enduring impairments. However, given the life-long plasticity of the brain one could assume that recovery could be facilitated by the harnessing of mechanisms underlying neuronal reorganization. Currently it is not clear how this reorganization can be mobilized. Novel technology based neurorehabilitation techniques hold promise to address this issue. Here we describe a Virtual Reality (VR) based system, the Rehabilitation Gaming System (RGS) that is based on a number of hypotheses on the neuronal mechanisms underlying recovery, the structure of training and the role of individualization. We investigate the psychometrics of the RGS in stroke patients and healthy controls.MethodsWe describe the key components of the RGS and the psychometrics of one rehabilitation scenario called Spheroids. We performed trials with 21 acute/subacute stroke patients and 20 healthy controls to study the effect of the training parameters on task performance. This allowed us to develop a Personalized Training Module (PTM) for online adjustment of task difficulty. In addition, we studied task transfer between physical and virtual environments. Finally, we assessed the usability and acceptance of the RGS as a rehabilitation tool.ResultsWe show that the PTM implemented in RGS allows us to effectively adjust the difficulty and the parameters of the task to the user by capturing specific features of the movements of the arms. The results reported here also show a consistent transfer of movement kinematics between physical and virtual tasks. Moreover, our usability assessment shows that the RGS is highly accepted by stroke patients as a rehabilitation tool.ConclusionsWe introduce a novel VR based paradigm for neurorehabilitation, RGS, which combines specific rehabilitative principles with a psychometric evaluation to provide a personalized and automated training. Our results show that the RGS effectively adjusts to the individual features of the user, allowing for an unsupervised deployment of individualized rehabilitation protocols. <s> BIB011 </s> Virtual Reality and Assistive Technologies: A Survey <s> Visual-feedback-based VEs for mobility impairments <s> Stroke is the leading cause of long term disability among adults in industrialized nations. The partial paralysis that stroke patients often experience can make independent living difficult or impossible. Research suggests that many of these patients could recover by performing hundreds of daily repetitions of motions with their affected limbs. Yet, only 31% of patients perform the exercises recommended by their therapists. Home-based stroke rehabilitation games may help motivate stroke patients to perform the necessary exercises to recover. In this paper, we describe a formative study in which we designed and user tested stroke rehabilitation games with both stroke patients and therapists. We describe the lessons we learned about what makes games useful from a therapeutic point of view. <s> BIB012 </s> Virtual Reality and Assistive Technologies: A Survey <s> Visual-feedback-based VEs for mobility impairments <s> Over the last 15 years, a virtual revolution has taken place in the use of Virtual Reality simulation technology for clinical purposes. Shifts in the social and scientific landscape have now set the stage for the next major movement in Clinical Virtual Reality with the "birth" of intelligent virtual humans. Seminal research and development has appeared in the creation of highly interactive, artificially intelligent and natural language capable virtual human agents that can engage real human users in a credible fashion. No longer at the level of a prop to add context or minimal faux interaction in a virtual world, virtual humans can be designed to perceive and act in a 3D virtual world, engage in spoken dialogues with real users and can be capable of exhibiting human-like emotional reactions. This paper will present an overview of the SimCoach project that aims to develop virtual human support agents to serve as online guides for promoting access to psychological healthcare information and for assisting military personnel and family members in breaking down barriers to initiating care. The SimCoach experience is being designed to attract and engage military Service Members, Veterans and their significant others who might not otherwise seek help with a live healthcare provider. It is expected that this experience will motivate users to take the first step - to empower themselves to seek advice and information regarding their healthcare and general personal welfare and encourage them to take the next step towards seeking more formal resources if needed. <s> BIB013
As demonstrated in Table 2 , visual feedback-based physical rehabilitation is classified into two subcategories: (1) VE without full body skeletal tracking and (2) VE with full body skeletal tracking. In VE-based rehabilitation systems that do not require full body skeletal tracking, movements are simple; tasks in a virtual environment involve movements of different body parts (i.e., wrist, arm, shoulder, knee, and more) or the whole body. Depending on the devices used as mentioned in Table 2, the following approaches towards rehabilitation have mainly been adopted under this subcategory: (i) camerabased, (ii) Wii-based and (iii) sensor-based. Different applications on these three approaches are discussed below. In camera-based applications, the user typically sits or stands in front of a camera and image-processing software is used to recognize arm and hand movements BIB002 . The user often wears colored gloves or other markers to enable data acquisition. The Rehabilitation Gaming System (RGS) was developed for arm rehabilitation of post-stroke patients where both of the patients arms were tracked by a camera and mapped onto the movements of two virtual arms on the display BIB011 . This system is demonstrated in Figure 2a . The game required continuous movement of patients arms in the real world to move the virtual arms to intercept a moving sphere as shown on the screen. As soon as the sphere was intercepted, a new position of the sphere was determined which again needed to be intercepted by the virtual arms. Data gloves were used to measure the finger movements. In order to intensify the degree of realism, instead of virtual limbs, Gesture Xtreme VR system incorporated patients live in-situ video into the VE BIB005 . Patients had to constantly move their hands, body, or feet in the real world to make things work in the VE. Figure 2b demonstrates how an individual with spinal cord injury interacting with the Birds and Balls game environment of Gesture Xtreme VR system by persistently moving his body to touch the moving balls to convert them to doves. Similarly, in Figure 2c , a stroke patient is seen to interact with Soccer game env ironment. Sviestrup et al. used a very similar technique to elicit shoulder movements, i.e., shoulder forward flexion, shoulder abduction and shoulder rotation among patients with chronic frozen shoulder BIB003 . Patients were superimposed in a virtual soccer game environment and were required to stop the ball from scoring. Multiple interactions and environments were designed to allow for the adjustment of the intensity and difficulty of the body movement. The same interactive VE had been used for balance rehabilitation of TBI patients. Patients were asked to perform several exercises, i.e., picking up objects from the floor, single versus double limb stance, moving within the base of support, walking, hopping, jumping, and jogging. Performance was measured on several issues such as single limb stance, lateral dodging, and stair descent. The VR-exercise group showed a remarkable change in balance and mobility in comparison with the conventional group. Burke et al. developed some webcam-based rehab games that involved single or bi-manual hand movements  ). In Rabbit Chase, a rabbit moved around from hole to hole and the user had to touch the rabbit with one hand as it would come out of the hole. In Arrow Attack, the user had to touch two arrows in a VE: one pointing to the left and another to the right with correct hands, i.e., with left hand and right hand respectively ( Figure 2d ). These games could be sped up or slowed down depending on the users performance. The users performance was appreciated by rewarding points after each successful completion and by honoring each try with enthusiastic auditory feedback or partial score. Playstation EyeToy is a low-cost, video-capture system that enables users to interact with virtual objects displayed on a TV screen via active movements of different body parts, i.e., hands, wrists, shoulders, and feet. In the Playstation game Kung Foo, participants repeatedly had to eliminate successive invading warriors by hitting them with the upper limbs; Goal Attack required movement of the whole body with more active movements of upper limbs; Mr. Chef involved cognitive input to prepare different fast food with limited movements of both hands (Figure 2e ). Yavuzer et al. evaluated Playstation EyeToy for the treatment of flexion/ extension of the paretic shoulder, elbow, and wrist as well as abduction of the paretic shoulder of post-stroke patients BIB008 ). In addition to conventional ther-apy, playing EyeToy games 5 days a week, 2 to 5 hour per day for four weeks was found to have a potential impact on the enhancement of upper extremity-related motor functioning among post-stroke patients. The Functional Independence Measure (FIM) instrument was used for the evaluation of upper extremity related motor functioning among post stroke patients. The self-care sub-items of FIM that relate to daily activities like eating, grooming, bathing, dressing upper body, dressing lower body, and toileting were considered for the evaluation. Subjects showed significant improvements in self-care activities. The SIGUS platform is a software environment that worked towards the betterment of the lives of quadriplegics. A training dataset associated with different facial features and head movements was created so that the user could associate different visual signs (facial expressions and movements, for instance), to each piece of a virtual drum. After initial calibration, the virtual drum could be played without any direct contact to a mouse or keyboard, just by reproducing a face in front of a standard webcam ( Figure 2f ). The software was extended with hand gestures and eye gaze BIB006 ). Similar to camera-based applications as discussed above, Wiimotes are widely used for the rehabilitation of shoulder, forearm, wrist and more ( The range of motion of the wrist was measured by attaching reflective tapes which were detected by the embedded infrared camera in the Wiimote. Subjects were found to have increased the range of motion of the wrist as they repeatedly played the game. Alankus et al. developed a number of Wii-based rehabilitation games while considering patients ability in different levels of recovery (i.e., available motions, cognitive skills, and performance) BIB012 ). In the Helicopter game, as a helicopter kept on flying horizontally in the scene, the player needed to move their hands vertically to let the helicopter collect fuel in the air while avoiding hitting the buildings at the same time. Figure 3a demonstrates a subject playing the game using a Wii remote strapped to the upper arm to detect shoulder flexion. Some Wii-games incorporated social context along with the cognitive input. Under the Sea is a two-player collaborative game which required two patients to move their hands to control and protect a mother fish and its trailing babies from a hungry predator; one player controlled mother fish and babies to collect and eat ferns; another player prevented a predator fish from reaching them. Proper hand coordination and successful control over the game let the patients earn points in the game. Baseball catch required the player screen out baseballs from other types of balls before a catch. To ensure correct muscle groups to be used for movements, additional Wiimotes were attached to the body parts that were supposed to remain stationary. For example, for a game that required only elbow movement, an additional Wiimote was also attached to the upper arm to detect and cancel out the compensation by the rest of the body (Figure 3b ). For wrist and arm rehabilitation, Burke et al. designed Wii-based Virtual vibraphone ). As the user selected a tune for play, each note of the tune gradually highlighted a bar on the virtual vibraphone to be hit with a virtual mallet. In order to play a note, the user had to move the virtual mallet to place it on the highlighted bar by pointing the Wii-remote followed by a press on the controller button. The users score was determined on the basis of how accurately the tune was played within the allocated time. A single user could play two notes simultaneously by holding two Wii-motes with both hands or multiple users could play the application together in a collaborative environment. Some Wii-based rehab exercises involve the movements of the whole body. Deutsch et al. conducted Wii-based rehab exercises on a patient suffering from cerebral palsy BIB009 ). The patient was asked to play a number of Wii-games (such as tennis, golf, boxing, and more) for practicing body movement often congruent with real-world motions. For example, the Wiimote was held with one hand for bowling, both hands for baseball, tennis or golf, and for boxing, one hand held the Wii-mote and the other a game controller. After undergoing Wii-rehabilitation therapy for a period of four weeks, the patient was reported to have better cognitive ability, more symmetrical posture, and better walking capability. Similar to Wiimote, sensor-based exergames are also quite popular for the rehabilitation of hands ). In Catch task developed by Burke et al., the user had to hold a real world basket with both hands while magnetic sensors were either attached to the users hands or the basket to catch falling oranges in a virtual basket (Figure 4 a). Game parameters such as the falling speed of oranges or the locus of oranges could be adjusted as per individual capabilities. In Whack a mouse, a mouse appeared at a random location for a few seconds to be whacked by a virtual hammer that was controlled by a sensor attached to the users hand ( Figure 4b ). Once the user could successfully adapt to this game, they became ready for the next level. In the next level, a dog randomly appeared on the scene and the user had to avoid hitting the dog while whacking the mouse. Adding different levels of difficulty develops a sense of self-competitiveness among the users which make exercises more challenging and engaging at the same time. Until now, different VR-based rehabilitation applications that do not require full body skeletal tracking were discussed. However, some rehabilitation approaches are about maintaining proper posture and necessitate full body skeletal tracking for continuous adjustment and improvement. Microsoft Kinect and different motion capture systems are used in such applications. Microsoft Kinect has been widely used for users skeletal tracking and posture determination. Guo et al. replaced existing key-board based movements of the car in an original game with Microsoft Kinect (Guo and Quarles 2013). The users movement was tracked by Microsoft Kinect. Correct body movement increased the speed of the car, incorrect performance resulted in little or no progress. In time-locked op-tion, the user needed to perform a particular cycle in an exercise (i.e., crouching and rising) within limited time, otherwise the game would be locked (5a). Other postures such as half-crouching stability did not have time constraints ( Figure  5 b ). Before the game started, participants had to stand for Kinect camera calibration and data initialization. A Bluetooth physiological sensor called Bioharness BT was used to monitor the heart rate. Experimental results demonstrated that participants were able to perform exercises longer with the game. Espinoza et al. designed Game Cane -a cane-based interface for 3D games for balance rehabilitation where Microsoft Kinect enabled body motion tracking (Espinoza, Cantu, and Quarles 2013). In Game Cane, cane interaction was mapped to game interaction (Figure 5c ). To make the user less dependent on the cane and gradually recover balance, an inverse relation was established between the exerted force on the cane and the progress in game. The Wii-mote facilitated interaction with the game and a force sensitive resistor (FSR) was placed at the bottom of the cane to detect the amount of force being applied on the cane (Figure 5d ). Rector et al. developed an audio/visual feedback based yoga exercise program named Eyes-free yoga for the blind and visually impaired to let them maintain an adequate fitness level ( Figure 5e ) (Rector, Bennett, and Kientz 2013). Microsoft Kinect was used for skeletal tracking of 20 body joints ( Figure 5f ). A set of rules for each pose was programmed. The exergame offered verbal adjustments and auditory confirmation to assist in pose improvement. Blind participants overall thoughts on eyes-free yoga were positive. As Kinect skeletal tracking does not adapt well to bent knees, poses needed to be compatible with Kinects skeletal tracking, which required users to be in a standing position. Though Microsoft Kinect is widely used for simple skeletal tracking of the body, some rehabilitation approaches necessitate a very accurate information about the posture of different joints of the body. This can be a stick figure or a virtual human to provide information about joint angles in the different phases of the gait cycle or a trainer avatar embedded into the trainees avatar to provide information about accurate posture ( Figure 6a ) (Kiefer, Rhea, and Warren 2013). Motion capture based skeletal tracking along with several retroreflective markers on the users body and several infrared cameras is able to provide a very accurate skeletal information of the subjects body. Chua et al. developed and evaluated a Tai chi training system which aimed to improve training for a full body motor task in an immersive VE by introducing a trainer avatar along with the subjects avatar BIB004 . Vicon optical motion capture system was used to compute the skeletal figure of the trainee student for further analysis of the virtual student and their virtual instructor. In the virtual Tai chi environment, the trainee student found himself paired with his virtual instructor in a calm and peaceful 3D virtual environment as shown to the right of Figure 6b . As the virtual instructor moved for a Tai chi posture, the student in the real world mimicked the virtual instructor and the virtual student was updated as per the joint data of the real student. The updated data was transmitted via a wireless video trans-mitter which was received by a light weight video receiver strapped to the students belt and displayed on the students HMD glass. In order to measure how closely the subject mimicked the teachers motion, a number of comparisons were made between different skeletal parts of the subject and the teacher. In some layout options, a stick figure of the teacher was superimposed inside the students transparent or wireframe body to help the student understand precise movements of the joints and adjust their movements based on the visual feedback. In order to elicit a better sense of presence, in addition to a responsive full body avatar of the subject himself, an avatar of the assistive device (such as a cane) carried by the subject in real world was also added to the VE (Guo, Samaraweera, and Quarles 2013). Subjects put on an HMD to navigate in the VE while retroreflective markers were fastened to the subjects body and the cane to be tracked by the motion capture system (Figure 6c ). In the VE, subjects with mobility impairments used walkways, stairways, and elevators to move around a fantasy castle with the help of a virtual cane as demonstrated in Figure 6d For example, users had to open the cupboard to access the soup can, move the knob of the stove to heat up the cooking surface, boil water, pour necessary ingredients into the can, and so on. In the VE, users were also provided with a series of visual prompts and cues to assist completion of each task. The virtual reality system was comprised of a PC platform and a head-mounted 3-dimensional display and the user interacted with the environment using either a mouse or joystick. Users actions were recorded for subsequent analysis and assessment and they scored points on successful completion of each task. After undergoing VR training over a certain period of time, patients showed a gradual improvement in behavior and were able to perform similar tasks with enhanced prowess in the real world. Parsons et al. exposed some students with autism spectrum disorder (ASD) to a virtual caf and virtual bus environment to be able to interpret the scenes meaningfully with the help of a facilitator BIB007 . The goal was to learn how to interact with people with appropriate social responses. In both scenarios, there were a number of levels of difficulty; the user's main aim was to find an appropriate place to sit, for example, sitting by oneself or with a stranger (after asking an appropriate ques-tion) ( Figure 7b ). Scenarios also included queuing appropriately, asking someone to move their bags so that they could sit down, and standing when there were no available seats. Verbal responses, providing both positive and negative feedback about the user's behavior, were pre-programmed into the environment and activated as per the users response. In a Desktop-based environment, user interaction was performed with a traditional mouse. Participants were found to be able to properly handle similar real life situations, i.e., in a caf or on a bus and there was a clear transfer of knowledge from VE to real environment. Herrara et al. let children with ASD shop in a touch screen-based virtual supermarket following a list BIB010 ). The goal was to let the children identify different objects and understand their functionalities and social context followed by imaginary transformation of the objects. For example, a pair of trousers were bought to dress up, but were also imagined as a road divided into two. An increased level of attention was observed among the participants on the retest compared to the initial test. The participants understanding of the functional use of each object in the supermarket helped them to use similar objects in a proper way in real life. Participants were also found to exhibit an increase in their ability to distinguish between imaginary and real objects. Rizzo et al. proposed an intelligent and highly interactive virtual human support agent in their SimCoach project to serve as an online healthcare guide or coach to military service members, veterans for promoting access to psychological healthcare information BIB013 . As these people return home from the battlefield, the horror of war keeps on haunting them; they feel stigma and insecurity regarding a clinical condition and tend to live an isolated life. A virtual human coach named SimCoach was designed to be able to engage in rich conversation (even able to recognize nonverbal cues of the user) and provide support and encouragement by increasing awareness, and if necessary, refer to medical practitioners for further diagnosis and treatment. Users would just need sign up to a web-based portal to have access to all services provided by SimCoach. Once logged in, users would be directed to virtual experts on specific areas such as stress, brain injury, marriage counseling, suicide, and so on. SimCoach would store user-specific information and be able to follow up on subsequent visits. Another application of VE as a cognitive therapy is phobia or hallucination desensitization BIB001 . This involves gradual exposure of the phobic individuals to circumstances that are increasingly close to the one they are scared of. A VE helps the clinician to measure patients stress level by monitoring their heartbeat and adjust the level of therapy accordingly by modifying it. Surez et al. developed a VR-based training as an effective psychotherapy to gradually shed off excessive fear of height. In the virtual training environment, subjects were taken by an elevator from the ground floor to the topmost floor of a high storey glass building to have a panoramic view of the surrounding landscape (Suárez, Santamara, and Claudio 2013). Similarly, it is easy to simulate a VE with phobiainducing stimuli such as cockroaches, spiders, and more and let the phobic patients confront them in VE so that they can gradually adapt to a similar real world environment. A VE had been recommended for the treatment of schizophrenic patients BIB001 . Those patients can be infused with virtual hallucinations so that their actual hallucinations can be gradually desensitized. A VE had also been successfully used for the treatment of social phobias such as fear of public speaking by letting people openly address a huge virtual crowd ( 