Perceiving distance in virtual reality: theoretical insights from contemporary technologies

Assessing visuospatial perception in clinical and healthy populations: Test-retest reliability and smallest real difference of hill steepness estimation and the distance-on-hill task in virtual reality

Theories of embodied perception posit that the visuospatial perception of one's environment is not only bound by features of the environmental itself, but also by the body capacity and affective state of the individual. Hill steepness and distance estimation tasks are widely used to assess the influence of physiological and psychological factors on visuospatial perception, but their test-retest reliability and measurement error are unknown. Such information is important to contextualise repeated measures study designs and understanding individual level differences. We aimed to evaluate the test-retest reliability and establish the smallest real difference (SRD) of three commonly used visuospatial perception tasks (ascending and descending hill steepness estimation, the distance-on-hill task) in healthy controls (n = 33) and people with painful knee osteoarthritis (n = 33). All participants completed the virtual reality visuospatial perception tasks two times, one week apart. Intraclass correlation coefficients (ICC), Bland-Altman plots, and SRD were used to evaluate the tasks. Our results revealed that both hill steepness estimation tasks are suitable for repeat administration in both populations given excellent reliability (uphill ICC = 0.80 to 0.85; downhill ICC = 0.89 to 0.90) and high sensitivity to change (uphill SRD = 17.7 to 18.9 degrees; downhill SRD = 12.1 to 14.7 degrees). The distance-on-hill task may have limited utility due to its poor reliability (ICC = 0.29 to 0.38) and low sensitivity to change (SRD = 6.20 to 8.5 m). Our findings provide methodological support for the use of hill steepness tasks as a measure of visuospatial perception in embodied perception research.

Viewers perceive shape in pictures according to per-fixation perspective

How viewers interpret different pictorial projections has been a longstanding question affecting many disciplines, including psychology, art, computer science, and vision science. The most-prominent theories assume that viewers interpret pictures according to a single linear perspective projection. Yet, no existing theory accurately describes viewers' perceptions across the wide variety of projections used throughout art history. Recently, Hertzmann hypothesized that pictorial 3D shape perception is interpreted according to a separate linear perspective for each eye fixation in a picture. We performed four experiments based on this hypothesis. The first two experiments found that viewers consider object depictions as more accurate when an object is projected according to its own local linear projection, rather than one consistent with the rest of the picture. In the third experiment, viewers exhibited change blindness to projections in peripheral vision, suggesting that perception of shape primarily occurs around fixations. The fourth experiment found surface slant compensation to be dependent on fixation. We conclude that pictorial shape perception operates according to per-fixation perspective.

Impact of Visual Virtual Scene and Localization Task on Auditory Distance Perception in Virtual Reality

Investigating auditory perception and cognition in realistic, controlled environments is made possible by virtual reality (VR). However, when visual information is presented, sound localization results from multimodal integration. Additionally, using head-mounted displays leads to a distortion of visual egocentric distances. With two different paradigms, we investigated the extent to which different visual scenes influence auditory distance perception, and secondary presence and realism. To be more precise, different room models were displayed via HMD while participants had to localize sounds emanating from real loudspeakers. In the first paradigm, we manipulated whether a room was congruent or incongruent to the physical room. In a second paradigm, we manipulated room visibility - displaying either an audiovisual congruent room or a scene containing almost no spatial information- and localization task. Participants indicated distances either by placing a virtual loudspeaker, walking, or verbal report. While audiovisual room incongruence had a detrimental effect on distance perception, no main effect of room visibility was found but an interaction with the task. Overestimation of distances was higher using the placement task in the non-spatial scene. The results suggest an effect of visual scene on auditory perception in VR implying a need for consideration e.g. in virtual acoustics research.

The exposure to body size distortions affects allocentric distance perception in extra-personal space

Previous research demonstrated that body size distortions induced by body illusion can influence spatial perception in near space. We investigated whether manipulating body size through a Full-Body Illusion-like paradigm influences allocentric distance perception in extra-personal space. Participants estimated the distance between landmarks in far space before and after a body illusion with standard or big bodies in anatomical (i.e., virtual and actual legs were aligned) or non-anatomical orientation (i.e., virtual legs were rotated by 45 degrees). We analysed space perception via Multidimensional Scaling for landmark configuration and distance misestimation. Embodiment occurred with bodies in anatomical orientation, while exposure to bigger bodies increased perceived distance, regardless of the presence of the embodiment. However, no significant changes emerged in the perception of landmark configuration. Findings indicated that, in extra-personal space, the distance perception between objects, rather than their shape configuration, is scaled based on a metric reference related to a seen body.

Obstacle Circumvention Strategies During Omnidirectional Treadmill Walking in Virtual Reality

Obstacle circumvention is an important task for community ambulation that is challenging to replicate in research and clinical environments. Omnidirectional treadmills combined with virtual reality (ODT-VR) offer a promising solution, allowing users to change walking direction and speed while walking in large, simulated environments. However, the extent to which such a setup yields circumvention strategies representative of overground walking in the real world (OVG-RW) remains to be determined. This study examined obstacle circumvention strategies in ODT-VR versus OVG-RW and measured how they changed with practice. Fifteen healthy young individuals walked while avoiding an interferer, performing four consecutive blocks of trials per condition. Distance at onset trajectory deviation, minimum distance from the interferer, and walking speed were compared across conditions and blocks. In ODT-VR, larger clearances and slower walking speeds were observed. In contrast, onset distances and proportions of right-side circumvention were similar between conditions. Walking speed increased from the first to the second block exclusively. Results suggest the use of a cautious locomotor behavior while using the ODT-VR setup, with some key features of circumvention strategies being preserved. Although ODT-VR setups offer exciting prospects for research and clinical applications, consideration should be given to the generalizability of findings to the real world.

Visual Perceptual Confidence: Exploring Discrepancies Between Self-reported and Actual Distance Perception In Virtual Reality

Virtual Reality (VR) systems are widely used, and it is essential to know if spatial perception in virtual environments (VEs) is similar to reality. Research indicates that users tend to underestimate distances in VR. Prior work suggests that actual distance judgments in VR may not always match the users self-reported preference of where they think they most accurately estimated distances. However, no explicit investigation evaluated whether user preferences match actual performance in a spatial judgment task. We used blind walking to explore potential dissimilarities between actual distance estimates and user-selected preferences of visual complexities, VE conditions, and targets. Our findings show a gap between user preferences and actual performance when visual complexities were varied, which has implications for better visual perception understanding, VR applications design, and research in spatial perception, indicating the need to calibrate and align user preferences and true spatial perception abilities in VR.

Painful distortions: people with painful knee osteoarthritis have biased visuospatial perception of the environment

ABSTRACT

Visuospatial perception is thought to be adaptive-ie, hills are perceived as steeper when capacity is low, or threat is high-guiding appropriate interaction with the environment. Pain (bodily threat) may similarly modulate visuospatial perception, with the extent of modulation influenced by threat magnitude (pain intensity, fear) and associated with behaviour (physical activity). We compared visuospatial perception of the environment between 50 people with painful knee osteoarthritis and 50 age-/sex-matched pain-free control participants using 3 virtual reality tasks (uphill steepness estimation, downhill steepness estimation, and a distance-on-hill measure), exploring associations between visuospatial perception, clinical characteristics (pain intensity, state and trait fear), and behaviour (wrist-worn accelerometry) within a larger knee osteoarthritis group (n = 85). People with knee osteoarthritis overestimated uphill (F 1,485 = 19.4, P < 0.001) and downhill (F 1,480 = 32.3, P < 0.001) steepness more so than pain-free controls, but the groups did not differ for distance-on-hill measures (U = 1273, P = 0.61). There was also a significant group x steepness interaction for the downhill steepness task (F 4,480 = 3.11, P = 0.02). Heightened overestimation in people with knee osteoarthritis relative to pain-free controls increased as downhill slopes became steeper. Results were unchanged in a replication analysis using all knee osteoarthritis participants (n = 85), except the downhill steepness interaction was no longer significant. In people with knee osteoarthritis, higher state fear was associated with greater over-estimation of downhill slope steepness (rho = 0.69, P < 0.001), and greater visuospatial overestimation (distance-on-hill) was associated with lower physical activity levels (rho = -0.22, P = 0.045). These findings suggest that chronic pain may shift perception of the environment in line with protection, with overestimation heightened when threat is greater (steeper hills, more fearful), although impact on real-world behaviour is uncertain.

Validating virtual reality for time perception research: Virtual reality changes expectations about the duration of physical processes, but not the sense of time

Immersive virtual reality (VR) provides a versatile method for investigating human time perception, because it allows the manipulation and control of relevant variables (e.g., the speed of environmental changes) that cannot be modified in the real world. However, an important premise for interpreting the results of VR studies, namely that the method itself does not affect time perception, has received little attention. Here we tested this assumption by comparing timing performance in a real environment and a VR scenario. Participants performed two timing tasks, requiring the production of intervals defined either by numerical values ("eight seconds") or by a physical process ("the time it takes for a bottle to run out when turned over"). We found that the experience of immersive VR exclusively altered judgments about the duration of physical processes, whereas judgments about the duration of abstract time units were unaffected. These results demonstrate that effects of VR on timing performance are not driven by changes in time perception itself, but rather by altered expectations regarding the duration of physical processes. The present study validates the use of VR in time perception research and strengthens the interpretation of changed timing behaviour induced by manipulations within VR.

Changes in Navigation Controls and Field-of-View Modes Affect Cybersickness Severity and Spatiotemporal Gait Patterns After Exposure to Virtual Environments

OBJECTIVE

To examine the effects of navigation controls and field-of-view modes on cybersickness severity and gait dynamics after cessation of exposure to a virtual environment (VE).

BACKGROUND

The applications of virtual reality are increasing in various fields; however, whether changes in interaction techniques and visual contents could mitigate the potential gait disturbance following VE exposure remains unclear.

METHOD

Thirty healthy adults wore a head-mounted display to complete six sessions of 12-min run-and-gun tasks using different navigation controls (gamepad, head, natural) and field-of-view modes (full, restricted). Forward and backward walking tasks were performed before and after VE exposure. The degrees of cybersickness and presence were evaluated using questionnaires, along with the in-session task performance. Spatiotemporal gait measures and their variabilities were calculated for each walking task.

RESULTS

The participants experienced less cybersickness with the head and natural controls than with the gamepad. Natural control, based on matching body movements, was associated with the highest degree of presence and best performance. VE navigation using the gamepad showed reduced cadences and increased stride times during postexposure forward-walking tasks. When the VE was presented via the restricted field-of-view mode, increased gait variabilities were observed from backward-walking tasks after VE exposure.

CONCLUSION

Body movement-based navigation controls may alleviate cybersickness. We observed gait adaptation during both ambulation tasks, which was influenced by the navigation control method and field-of-view mode.

APPLICATION

This study provides the first evidence for gait adaptation during balance-demanding tasks after VE exposure, which is valuable for designing guidelines for virtual reality interactions.

Linear perspective cues have a greater effect on the perceptual rescaling of distant stimuli than textures in the virtual environment

The presence of pictorial depth cues in virtual environments is important for minimising distortions driven by unnatural viewing conditions (e.g., vergence-accommodation conflict). Our aim was to determine how different pictorial depth cues affect size constancy in virtual environments under binocular and monocular viewing conditions. We systematically removed linear perspective cues and textures of a hallway in a virtual environment. The experiment was performed using the method of constant stimuli. The task required participants to compare the size of 'far' (10 m) and 'near' (5 m) circles displayed inside a virtual environment with one or both or none of the pictorial depth cues. Participants performed the experiment under binocular and monocular viewing conditions while wearing a virtual reality headset. ANOVA revealed that size constancy was greater for both the far and the near circles in the virtual environment with pictorial depth cues compared to the one without cues. However, the effect of linear perspective cues was stronger than textures, especially for the far circle. We found no difference between the binocular and monocular viewing conditions across the different virtual environments. We conclude that linear perspective cues exert a stronger effect than textures on the perceptual rescaling of far stimuli placed in the virtual environment, and that this effect does not vary between binocular and monocular viewing conditions.

Investigating and acquiring motor expertise using virtual reality

After just months of simulated training, on January 19, 2019 a 23-year-old E-sports pro-gamer, Enzo Bonito, took to the racetrack and beat Lucas di Grassi, a Formula E and ex-Formula 1 driver with decades of real-world racing experience. This event raised the possibility that practicing in virtual reality can be surprisingly effective for acquiring motor expertise in real-world tasks. Here, we evaluate the potential of virtual reality to serve as a space for training to expert levels in highly complex real-world tasks in time windows much shorter than those required in the real world and at much lower financial cost without the hazards of the real world. We also discuss how VR can also serve as an experimental platform for exploring the science of expertise more generally.

New Approaches to 3D Vision

New approaches to 3D vision are enabling new advances in artificial intelligence and autonomous vehicles, a better understanding of how animals navigate the 3D world, and new insights into human perception in virtual and augmented reality. Whilst traditional approaches to 3D vision in computer vision (SLAM: simultaneous localization and mapping), animal navigation (cognitive maps), and human vision (optimal cue integration) start from the assumption that the aim of 3D vision is to provide an accurate 3D model of the world, the new approaches to 3D vision explored in this issue challenge this assumption. Instead, they investigate the possibility that computer vision, animal navigation, and human vision can rely on partial or distorted models or no model at all. This issue also highlights the implications for artificial intelligence, autonomous vehicles, human perception in virtual and augmented reality, and the treatment of visual disorders, all of which are explored by individual articles. This article is part of a discussion meeting issue 'New approaches to 3D vision'.