Virtual reality as a tool to explore multisensory processing before and after engagement in physical activity.

Introduction: This pilot study employed a non-randomized control trial design to explore the impact of physical activity within a virtual reality (VR) environment on multisensory processing among community-dwelling older adults. Methods: The investigation compared both chronic (over 6 weeks) and acute effects of VR-based physical activity to a reading control group. The evaluation metrics for multisensory processing included audiovisual response time (RT), simultaneity judgments (SJ), sound-induced flash illusion (SIFI), and temporal order judgments (TOJ). A total of 13 older adults were provided with VR headsets featuring custom-designed games, while another 14 older adults were assigned to a reading-based control group. Results: Results indicated that acute engagement in physical activity led to higher accuracy in the SIFI task (experimental group: 85.6%; control group: 78.2%; p = 0.037). Additionally, both chronic and acute physical activity resulted in quicker response times (chronic: experimental group = 336.92; control group = 381.31; p = 0.012; acute: experimental group = 333.38; control group = 383.09; p = 0.006). Although the reading group showed a non-significant trend for greater improvement in mean RT, covariate analyses revealed that this discrepancy was due to the older age of the reading group. Discussion: The findings suggest that immersive VR has potential utility for enhancing multisensory processing in older adults. However, future studies must rigorously control for participant variables like age and sex to ensure more accurate comparisons between experimental and control conditions.

Perceived timing of postural instability onset.

BACKGROUND: This study investigates the perceived onset of postural instability, a critical aspect of balance. Prior research using Temporal Order Judgment (TOJ) tasks revealed that postural perturbations must occur significantly earlier than an auditory reference stimulus for individuals to perceive them as simultaneous. However, there are methodological concerns with this previous work, particularly an unbalanced stimulus onset asynchrony (SOA) distribution. RESEARCH QUESTION: Does the point of subjective simultaneity (PSS) between postural perturbation onset and an auditory reference stimulus differ between SOA distributions unequally (distribution 1) and equally (distribution 2) distributed around true simultaneity (0 ms)? METHODS: A repeated measures design was employed, presenting two different SOA distributions to 10 participants using a TOJ task during both distribution 1 (88 trials) and distribution 2 (72 trials) SOA distributions. Paired t-tests were used to determine if there was a significant difference between the PSS of distribution 1 and 2. One-sample t-tests were also performed on the PSS values of both conditions in comparison to 0 ms (defined as true simultaneity) to determine if perceptual responses were delayed. RESULTS: Distribution 1 led to a perceived delay of postural instability onset by 20.34 ms, while distribution 2 resulted in a perceived delay of the auditory stimulus of 3.52 ms. However, neither condition was significantly different from each other nor from true simultaneity. SIGNIFICANCE: These findings suggest that the perception of postural instability onset is not slow, contrary to previous beliefs, and emphasize the importance of controlling methodological parameters when examining sensory cues. This understanding will help inform falls prevention strategies.

Off-Vertical Body Orientation Delays the Perceived Onset of Visual Motion.

The integration of vestibular, visual and body cues is a fundamental process in the perception of self-motion and is commonly experienced in an upright posture. However, when the body is tilted in an off-vertical orientation these signals are no longer aligned relative to the influence of gravity. In this study, the perceived timing of visual motion was examined in the presence of sensory conflict introduced by manipulating the orientation of the body, generating a mismatch between body and vestibular cues due to gravity and creating an ambiguous vestibular signal of either head tilt or translation. In a series of temporal-order judgment tasks, participants reported the perceived onset of a visual scene simulating rotation around the yaw axis presented in virtual reality with a paired auditory tone while in an upright, supine and side-recumbent body position. The results revealed that the perceived onset of visual motion was further delayed from zero (i.e., true simultaneity between visual onset and a reference auditory tone) by approximately an additional 30 ms when viewed in a supine or side-recumbent orientation compared to an upright posture. There were also no significant differences in the timing estimates of the visual motion between all the non-upright orientations. This indicates that the perceived timing of visual motion is negatively impacted by the presence of conflict in the vestibular and body signals due to the direction of gravity and body orientation, even when the mismatch is not in the direct plane of the axis of rotation.

Assessing the Effects of Exercise, Cognitive Demand, and Rest on Audiovisual Multisensory Processing in Older Adults: A Pilot Study.

A single bout of aerobic exercise is related to positive changes in higher-order cognitive function among older adults; however, the impact of aerobic exercise on multisensory processing remains unclear. Here we assessed the effects of a single bout of aerobic exercise on commonly utilized tasks that measure audiovisual multisensory processing: response time (RT), simultaneity judgements (SJ), and temporal-order judgements (TOJ), in a pilot study. To our knowledge this is the first effort to investigate the effects of three well-controlled intervention conditions on multisensory processing: resting, completing a cognitively demanding task, and performing aerobic exercise for 20 minutes. Our results indicate that the window of time within which stimuli from different modalities are integrated and perceived as simultaneous (temporal binding window; TBW) is malleable and changes after each intervention condition for both the SJ and TOJ tasks. Specifically, the TBW consistently became narrower post exercise while consistently increasing in width post rest, suggesting that aerobic exercise may improve temporal perception precision via broad neural change rather than targeting the specific networks that subserve either the SJ or TOJ tasks individually. The results from the RT task further support our findings of malleability of the multisensory processing system, as changes in performance, as assessed through cumulative probability models, were observed after each intervention condition. An increase in integration (i.e., greater magnitude of multisensory effect) however, was only found after a single bout of aerobic exercise. Overall, our results indicate that exercise uniquely affects the central nervous system and may broadly affect multisensory processing.

Binocular Viewing Facilitates Size Constancy for Grasping and Manual Estimation.

A prerequisite for efficient prehension is the ability to estimate an object's distance and size. While most studies demonstrate that binocular viewing is associated with a more efficient grasp programming and execution compared to monocular viewing, the factors contributing to this advantage are not fully understood. Here, we examined how binocular vision facilitates grasp scaling using two tasks: prehension and manual size estimation. Participants (n = 30) were asked to either reach and grasp an object or to provide an estimate of an object's size using their thumb and index finger. The objects were cylinders with a diameter of 0.5, 1.0, or 1.5 cm placed at three distances along the midline (40, 42, or 44 cm). Results from a linear regression analysis relating grip aperture to object size revealed that grip scaling during monocular viewing was reduced similarly for both grasping and estimation tasks. Additional analysis revealed that participants adopted a larger safety margin for grasping during monocular compared to binocular viewing, suggesting that monocular depth cues do not provide sufficient information about an object's properties, which consequently leads to a less efficient grasp execution.

Immersive Virtual Reality Exergames to Promote the Well-being of Community-Dwelling Older Adults: Protocol for a Mixed Methods Pilot Study.

BACKGROUND: Despite the proven benefits of exercise in older adults, challenges such as access and motivation can deter their engagement. Interactive virtual reality (VR) games combined with exercise (exergames) are a plausible strategy to encourage physical activity among this population. However, there has been little research on the feasibility, acceptability, and potential benefits of deploying at-home VR exergames among community-dwelling older adults. OBJECTIVE: The objectives of this study are to estimate the feasibility, usability, and acceptability of a co-designed VR exergame in community-dwelling older adults; examine intervention feasibility and assessment protocols for a future large-scale trial; and provide pilot data on outcomes of interest (physical activity, exercise self-efficacy, mood, cognition, perception, and gameplay metrics). METHODS: The study will be a remote, 6-week intervention comprising an experimental and a control group. A sample of at least 12 community-dwelling older adults (with no or mild cognitive impairment) will be recruited for each group. Both groups will follow the same study procedures and assessment methods. However, the experimental group will engage with a co-designed VR exergame (Seas The Day) thrice weekly for approximately 20 minutes using the Oculus Quest 2 (Facebook Reality Labs) VR headset. The control group will read (instead of playing Seas The Day) thrice weekly for approximately 20 minutes over the 6-week period. A mixed methods evaluation will be used. Changes in physical activity, exercise self-efficacy, mood, cognition, and perception will be compared before and after acute data as well as before and after the 6 weeks between the experimental (exergaming) and control (reading) groups. Qualitative data from postintervention focus groups or interviews and informal notes and reports from all participants will be analyzed to assess the feasibility of the study protocol. Qualitative data from the experimental group will also be analyzed to assess the feasibility, usability, and acceptability of at-home VR exergames and explore perceived facilitators of and barriers to uptaking VR systems among community-dwelling older adults. RESULTS: The screening and recruitment process for the experimental group started in May 2021, and the data collection process will be completed by September 2021. The timeline of the recruitment process for the control group is September 2021 to December 2021. We anticipate an estimated adherence rate of ≥80%. Challenges associated with VR technology and the complexity of remote assessments are expected. CONCLUSIONS: This pilot study will provide important information on the feasibility, acceptability, and usability of a custom-made VR exergaming intervention to promote older adults' well-being. Findings from this study will be useful to inform the methodology, design, study procedures, and assessment protocol for future large-scale trials of VR exergames with older adults as well as deepen the understanding of remote deployment and at-home use of VR for exercise in older adults. INTERNATIONAL REGISTERED REPORT IDENTIFIER (IRRID): DERR1-10.2196/32955.

Influence of Sensory Conflict on Perceived Timing of Passive Rotation in Virtual Reality.

Integration of incoming sensory signals from multiple modalities is central in the determination of self-motion perception. With the emergence of consumer virtual reality (VR), it is becoming increasingly common to experience a mismatch in sensory feedback regarding motion when using immersive displays. In this study, we explored whether introducing various discrepancies between the vestibular and visual motion would influence the perceived timing of self-motion. Participants performed a series of temporal-order judgements between an auditory tone and a passive whole-body rotation on a motion platform accompanied by visual feedback using a virtual environment generated through a head-mounted display. Sensory conflict was induced by altering the speed and direction by which the movement of the visual scene updated relative to the observer's physical rotation. There were no differences in perceived timing of the rotation without vision, with congruent visual feedback and when the speed of the updating of the visual motion was slower. However, the perceived timing was significantly further from zero when the direction of the visual motion was incongruent with the rotation. These findings demonstrate the potential interaction between visual and vestibular signals in the temporal perception of self-motion. Additionally, we recorded cybersickness ratings and found that sickness severity was significantly greater when visual motion was present and incongruent with the physical motion. This supports previous research regarding cybersickness and the sensory conflict theory, where a mismatch between the visual and vestibular signals may lead to a greater likelihood for the occurrence of sickness symptoms.

Evaluating the Effect of Semantic Congruency and Valence on Multisensory Integration.

Previous studies have found that semantics, the higher-level meaning of stimuli, can impact multisensory integration; however, less is known about the effect of valence, an affective response to stimuli. This study investigated the effects of both semantic congruency and valence of non-speech audiovisual stimuli on multisensory integration via response time (RT) and temporal-order judgement (TOJ) tasks [assessing processing speed (RT), Point of Subjective Simultaneity (PSS), and time window when multisensory stimuli are likely to be perceived as simultaneous (temporal binding window; TBW)]. Through an online study with 40 participants (mean age: 26.25 years; females = 17), we found that both congruence and valence had a significant main effect on RT (congruency and positive valence decrease RT) and an interaction effect (congruent/positive valence condition being significantly faster than all others). For TOJ, there was a significant main effect of valence and a significant interaction effect where positive valence (compared to negative valence) and the congruent/positive condition (compared to all other conditions) required visual stimuli to be presented significantly earlier than auditory stimuli to be perceived as simultaneous. A subsequent analysis showed a positive correlation between TBW width and RT (as TBW widens, RT increases) for the categories that were furthest from true simultaneity in their PSS (Congruent/Positive and Incongruent/Negative). This study provides new evidence that supports previous research on semantic congruency and presents a novel incorporation of valence into behavioural responses.

Immersive Virtual Reality Exergames for Persons Living With Dementia: User-Centered Design Study as a Multistakeholder Team During the COVID-19 Pandemic.

BACKGROUND: Advancements in supporting personalized health care and well-being using virtual reality (VR) have created opportunities to use immersive games to support a healthy lifestyle for persons living with dementia and mild cognitive impairment (MCI). Collaboratively designing exercise video games (exergames) as a multistakeholder team is fundamental to creating games that are attractive, effective, and accessible. OBJECTIVE: This research extensively explores the use of human-centered design methods that involve persons living with dementia in long-term care facilitates, exercise professionals, content developers, game designers, and researchers in the creation of VR exergames targeting physical activity promotion for persons living with dementia/MCI. METHODS: Conceptualization, collaborative design, and playtesting activities were carried out to design VR exergames to engage persons living with dementia in exercises to promote upper limb flexibility, strength, and aerobic endurance. We involved a total of 7 persons living with dementia/MCI, 5 exercise professionals, 5 community-dwelling older adults, a VR company for content creation, and a multidisciplinary research team with game designers, engineers, and kinesiology experts. RESULTS: An immersive VR exergame called Seas the Day was jointly designed and developed and it is freely available to be played in state-of-the-art VR headsets (Oculus Quest 1, 2). A model for the triadic interaction (health care institution, industry partner, academia) is also presented to illustrate how different stakeholders contribute to the design of VR exergames that consider/complement complex needs, preferences, and motivators of an underrepresented group of end users. CONCLUSIONS: This study provides evidence that a collaborative multistakeholder design results in more tailored and context-aware VR games for persons living with dementia. The insights and lessons learned from this research can be used by others to co-design games, including remote engagement techniques that were used during the COVID-19 pandemic.

Can the Perceived Timing of Multisensory Events Predict Cybersickness?

Humans are constantly presented with rich sensory information that the central nervous system (CNS) must process to form a coherent perception of the self and its relation to its surroundings. While the CNS is efficient in processing multisensory information in natural environments, virtual reality (VR) poses challenges of temporal discrepancies that the CNS must solve. These temporal discrepancies between information from different sensory modalities leads to inconsistencies in perception of the virtual environment which often causes cybersickness. Here, we investigate whether individual differences in the perceived relative timing of sensory events, specifically parameters of temporal-order judgement (TOJ), can predict cybersickness. Study 1 examined audiovisual (AV) TOJs while Study 2 examined audio-active head movement (AAHM) TOJs. We deduced metrics of the temporal binding window (TBW) and point of subjective simultaneity (PSS) for a total of 50 participants. Cybersickness was quantified using the Simulator Sickness Questionnaire (SSQ). Study 1 results (correlations and multiple regression) show that the oculomotor SSQ shares a significant yet positive correlation with AV PSS and TBW. While there is a positive correlation between the total SSQ scores and the TBW and PSS, these correlations are not significant. Therefore, although these results are promising, we did not find the same effect for AAHM TBW and PSS. We conclude that AV TOJ may serve as a potential tool to predict cybersickness in VR. Such findings will generate a better understanding of cybersickness which can be used for development of VR to help mitigate discomfort and maximize adoption.

Seas the day: Co-designing immersive virtual reality exergames with exercise professionals and people living with dementia.

BACKGROUND: Physical activity (PA) is associated with physical and cognitive benefits among people living with dementia or mild cognitive impairment (PLWD/MCI) and is a meaningful activity that can improve their confidence in everyday life. Exercising in virtual reality environments (VR Exergame) is becoming an increasingly feasible and enjoyable way to promote PA and well-being in PLWD/MCI. Although co-design can significantly improve the design of technology, it is rarely done with PLWD/MCI. This study uses participatory design methods and collaborative approaches to involve key stakeholders to develop and test a VR Exergame "Seas the Day", a novel solution targeting PLWD/MCI well-being. METHODS: A multi-stage, user-centered co-design approach was used to custom-build VR Exergames tailored to the unique needs and abilities of PLWD/MCI based on a first generation of the prototype that was previously developed and tested with PLWD/MCI. This paper describes the next iteration of the prototype. Processes included concept ideation and brainstorming activities, iterative prototyping, and playtesting/input/feedback sessions with key stakeholders (PLWD/MCI, exercise professionals, engineers, VR game designers, content developers). RESULTS: The multidisciplinary and collaborative design process occurred over 15 months (overlapping with COVID-19 pandemic) with 7 PLWD/MCI (6 females; M=81.3 years) and 9 exercise professionals (7 females; M=38.1 years) to date. The game was designed to target movements identified by exercise professionals and researchers (aerobic exercises, range of motion, seated-balance, quick response to stimuli) and is structured in three exercise stages (warm-up, conditioning, cool-down). To ensure safety of participants while using VR headsets, only seated upper-limb exercises were targeted. Stakeholder feedback regarding game mechanics, aesthetics, and visual/auditory cues were gathered during brainstorming and playtesting sessions and implemented into specific game-related scenarios (tai-chi, rowing, fishing). CONCLUSION: We presented the process, outcomes, and challenges of adopting a participatory/collaborative approach with multiple stakeholder groups to co-design VR Exergames tailored to PLWD/MCI. Next steps will include a mixed-method evaluation of the VR Exergames among community-dwelling older adults and PLWD/MCI in retirement communities and long-term care to evaluate: i) feasibility and acceptability of use, ii) game user experience, iii) barriers/facilitators to uptake of VR Exergames; and iv) inform/validate VR Exergames gameplay metrics reflective of cognitive and motor performance.

A Scoping Review of Audiovisual Integration Methodology: Screening for Auditory and Visual Impairment in Younger and Older Adults.

With the rise of the aging population, many scientists studying multisensory integration have turned toward understanding how this process may change with age. This scoping review was conducted to understand and describe the scope and rigor with which researchers studying audiovisual sensory integration screen for hearing and vision impairment. A structured search in three licensed databases (Scopus, PubMed, and PsychInfo) using the key concepts of multisensory integration, audiovisual modality, and aging revealed 2,462 articles, which were screened for inclusion by two reviewers. Articles were included if they (1) tested healthy older adults (minimum mean or median age of 60) with younger adults as a comparison (mean or median age between 18 and 35), (2) measured auditory and visual integration, (3) were written in English, and (4) reported behavioral outcomes. Articles that included the following were excluded: (1) tested taste exclusively, (2) tested olfaction exclusively, (3) tested somatosensation exclusively, (4) tested emotion perception, (5) were not written in English, (6) were clinical commentaries, editorials, interviews, letters, newspaper articles, abstracts only, or non-peer reviewed literature (e.g., theses), and (7) focused on neuroimaging without a behavioral component. Data pertaining to the details of the study (e.g., country of publication, year of publication, etc.) were extracted, however, of higher importance to our research question, data pertaining to screening measures used for hearing and vision impairment (e.g., type of test used, whether hearing- and visual-aids were worn, thresholds used, etc.) were extracted, collated, and summarized. Our search revealed that only 64% of studies screened for age-abnormal hearing impairment, 51% screened for age-abnormal vision impairment, and that consistent definitions of normal or abnormal vision and hearing were not used among the studies that screened for sensory abilities. A total of 1,624 younger adults and 4,778 older participants were included in the scoping review with males composing approximately 44% and females composing 56% of the total sample and most of the data was obtained from only four countries. We recommend that studies investigating the effects of aging on multisensory integration should screen for normal vision and hearing by using the World Health Organization's (WHO) hearing loss and visual impairment cut-off scores in order to maintain consistency among other aging researchers. As mild cognitive impairment (MCI) has been defined as a "transitional" or a "transitory" stage between normal aging and dementia and because approximately 3-5% of the aging population will develop MCI each year, it is therefore important that when researchers aim to study a healthy aging population, that they appropriately screen for MCI. One of our secondary aims was to determine how often researchers were screening for cognitive impairment and the types of tests that were used to do so. Our results revealed that only 55 out of 72 studies tested for neurological and cognitive function, and only a subset used standardized tests. Additionally, among the studies that used standardized tests, the cut-off scores used were not always adequate for screening out mild cognitive impairment. An additional secondary aim of this scoping review was to determine the feasibility of whether a meta-analysis could be conducted in the future to further quantitatively evaluate the results (i.e., are the findings obtained from studies using self-reported vision and hearing impairment screening methods significantly different from those measuring vision and hearing impairment in the lab) and to assess the scope of this problem. We found that it may not be feasible to conduct a meta-analysis with the entire dataset of this scoping review. However, a meta-analysis can be conducted if stricter parameters are used (e.g., focusing on accuracy or response time data only). Systematic Review Registration: https://doi.org/10.17605/OSF.IO/GTUHD.

Reduction of cybersickness during and immediately following noisy galvanic vestibular stimulation.

The mechanism underlying cybersickness during virtual reality (VR) exposure is still poorly understood, although research has highlighted a causal role for visual-vestibular sensory conflict. Recently established methods for reducing cybersickness include galvanic vestibular stimulation (GVS) to mimic absent vestibular cues in VR, or vibration of the vestibular organs to add noise to the sensory modality. Here, we examined if applying noise to the vestibular system using noisy-current GVS affects sickness severity in VR. Participants were exposed to one of the two VR games that were classified as either moderately or intensely nauseogenic. The VR content lasted for 50 min and was broken down into three blocks: 30 min of gameplay during exposure to either noisy GVS (± 1750 µA) or sham stimulation (0 µA), and 10 min of gameplay before and after this block. We characterized the effects of noisy GVS in terms of post-minus-pre-exposure cybersickness scores. In the intense VR condition, we found a main effect of noisy vestibular stimulation on a verbal cybersickness scale, but not for questionnaire measures of cybersickness. Participants reported lower cybersickness scores during and directly after exposure to GVS. However, this difference was quickly extinguished (~ 3-6 min) after further VR exposure, indicating that sensory adaptation did not persist after stimulation was terminated. In contrast, there were no differences between the sham and GVS group for the moderate VR content. The results show the potential for reducing cybersickness with non-invasive sensory stimulation. We address possible mechanisms for the observed effects, including noise-induced sensory re-weighting.

Visual Self-Motion Feedback Affects the Sense of Self in Virtual Reality.

We assessed how self-motion affects the visual representation of the self. We constructed a novel virtual-reality experiment that systematically varied an avatar's motion and also biological sex. Participants were presented with pairs of avatars that visually represented the participant ('self-avatar'), or another person ('opposite avatar'). Avatar motion either corresponded with the participant's motion, or was decoupled from the participant's motion. The results show that participants identified with (i) 'self-avatars' over 'opposite-avatars', (ii) avatars moving congruently with self-motion over incongruent motion, and importantly (iii) with the 'opposite avatar' over the 'self-avatar' when the opposite avatar's motion was congruent with self-motion. Our results suggest that both self-motion and biological sex are relevant to the body schema and body image and that congruent bottom-up visual feedback of self-motion is particularly important for the sense of self and capable of overriding top-down self-identification factors such as biological sex.

Temporal Metrics of Multisensory Processing Change in the Elderly.

Older adults exhibit greater multisensory response time (RT) facilitation by violating the race model more than young adults; this is commonly interpreted as an enhancement in perception. Older adults typically exhibit wider temporal binding windows (TBWs) and points of subjective simultaneity (PSS) that typically lie farther from true simultaneity as compared to young adults when simultaneity judgment (SJ) and temporal-order judgment (TOJ) tasks are utilized; this is commonly interpreted as an impairment in perception. Here we explore the relation between the three tasks in order to better assess audiovisual multisensory temporal processing in both young and older adults. Our results confirm previous reports showing that audiovisual RT, TBWs and PSSs change with age; however, we show for the first time a significant positive relation between the magnitude of race model violation in young adults as a function of the PSS obtained from the audiovisual TOJ task (r: 0.49, p: 0.007), that is absent in older adults (r: 0.13, p: 0.58). Furthermore, we find no evidence for the relation between race model violation as a function of the PSS obtained from the audiovisual SJ task in both young (r: -0.01, p: 0.94) and older adults (r: 0.1, p: 0.66). Our results confirm previous reports that (i) audiovisual temporal processing changes with age; (ii) distinct processes are likely involved in simultaneity and temporal-order perception; and (iii) common processing between race model violation and temporal-order judgment is impaired in the elderly.

Movement-Contingent Time Flow in Virtual Reality Causes Temporal Recalibration.

Virtual reality (VR) provides a valuable research tool for studying what occurs when sensorimotor feedback loops are manipulated. Here we measured whether exposure to a novel temporal relationship between action and sensory reaction in VR causes recalibration of time perception. We asked 31 participants to perform time perception tasks where the interval of a moving probe was reproduced using continuous or discrete motor methods. These time perception tasks were completed pre- and post-exposure to dynamic VR content in a block-counterbalanced order. One group of participants experienced a standard VR task ("normal-time"), while another group had their real-world movements coupled to the flow of time in the virtual space ("movement contingent time-flow; MCTF"). We expected this novel action-perception relationship to affect continuous motor time perception performance, but not discrete motor time perception. The results indicated duration-dependent recalibration specific to a motor task involving continuous movement such that the probe intervals were under-estimated by approximately 15% following exposure to VR with the MCTF manipulation. Control tasks in VR and non-VR settings produced similar results to those of the normal-time VR group, confirming the specificity of the MCTF manipulation. The findings provide valuable insights into the potential impact of VR on sensorimotor recalibration. Understanding this process will be valuable for the development and implementation of rehabilitation practices.

Presence and Cybersickness in Virtual Reality Are Negatively Related: A Review.

In order to take advantage of the potential offered by the medium of virtual reality (VR), it will be essential to develop an understanding of how to maximize the desirable experience of "presence" in a virtual space ("being there"), and how to minimize the undesirable feeling of "cybersickness" (a constellation of discomfort symptoms experienced in VR). Although there have been frequent reports of a possible link between the observer's sense of presence and the experience of bodily discomfort in VR, the amount of literature that discusses the nature of the relationship is limited. Recent research has underlined the possibility that these variables have shared causes, and that both factors may be manipulated with a single approach. This review paper summarizes the concepts of presence and cybersickness and highlights the strengths and gaps in our understanding about their relationship. We review studies that have measured the association between presence and cybersickness, and conclude that the balance of evidence favors a negative relationship between the two factors which is driven principally by sensory integration processes. We also discuss how system immersiveness might play a role in modulating both presence and cybersickness. However, we identify a serious absence of high-powered studies that aim to reveal the nature of this relationship. Based on this evidence we propose recommendations for future studies investigating presence, cybersickness, and other related factors.

Gravity-dependent change in the 'light-from-above' prior.

In environments where orientation is ambiguous, the visual system uses prior knowledge about lighting coming from above to recognize objects, determine which way is up, and reorient the body. Here we investigated the extent with which assumed light from above preferences are affected by body orientation and the orientation of the retina relative to gravity. We tested the ability to extract shape-from-shading with seven human male observers positioned in multiple orientations relative to gravity using a modified KUKA anthropomorphic robot arm. Observers made convex-concave judgments of a central monocularly viewed stimulus with orientations of a shading gradient consistent with being lit from one of 24 simulated illumination directions. By positioning observers in different roll-tilt orientations relative to gravity and when supine, we were able to monitor change in the light-from-above prior (the orientation at which a shaded disk appears maximally convex). The results confirm previous findings that the light-from-above prior changes with body orientation relative to gravity. Interestingly, the results varied also with retinal orientation as well as an additional component that was approximately twice the frequency of retinal orientation. We use a modelling approach to show that the data are well predicted by summing retinal orientation with cross-multiplied utricle and saccule signals of the vestibular system, yielding gravity-dependent biases in the ability to extract shape-from-shading. We conclude that priors such as light coming from above appear to be constantly updated by neural processes that monitor self-orientation to achieve optimal object recognition over moderate deviations from upright posture at the cost of poor recognition when extremely tilted relative to gravity.

Perceived timing of active head movement at different speeds.

The central nervous system must determine which sensory events occur at the same time. Actively moving the head corresponds with large changes in the relationship between the observer and the environment, sensorimotor processing, and spatiotemporal perception. Active head movement perception has been shown to be dependent on head movement velocity where participants who move their head fastest require the head to move earlier than comparison stimuli for perceived simultaneity more so than those who move their head slower. Such between-subject results cannot address whether active head movement perception changes with velocity. The present study used a within-subjects design to measure the point of subjective simultaneity (PSS) between active head movement speeds and a comparison sound stimulus to characterize the relationship between the velocity and perception of head movement onset. Our results clearly show that i) head movement perception is faster with faster head movements within-subjects, ii) active head movement onset must still precede the onset of other sensory events (average PSS: -123 ms to -52 ms; median PSS: -42 ms to -100 ms) in order to be perceived as occurring simultaneously even at the fastest speeds (average peak velocity: 76°/s-257°/s; median peak velocity 72 ms-257 ms). We conclude that head movement perception is slow, but that this delay is minimized with increased speed. These within-subject results are contrary to previous and present study between-subject results and are in agreement with literature where perception of auditory, visual and vestibular stimulus onset is less delayed with increased stimulus intensity.