Walking with Virtual People: Evaluation of Locomotion Interfaces in Dynamic Environments

Virtual Crowds Rheology: Evaluating the Effect of Character Representation on User Locomotion in Crowds

Crowd data is a crucial element in the modeling of collective behaviors, and opens the way to simulation for their study or prediction. Given the difficulty of acquiring such data, virtual reality is useful for simplifying experimental processes and opening up new experimental opportunities. This comes at the cost of the need to assess the biases introduced by the use of this technology. Our paper is part of this effort, and investigates the effect of the graphical representation of a crowd on the behavior of a user immersed within. More specifically, we inspect the virtual navigation through virtual crowds, in terms of travel speeds and local navigation choices as a function of the visual representation of the virtual agents that make up the crowd (simple geometric model, anthropomorphic model or realistic model). Through an experiment in which we ask a user to navigate virtual crowds of varying densities, we show that the effect of the visual representation is limited, but that an anthropomorphic representation offers the best trade-off between computational complexity and ecological validity, even though a more realistic representation can be preferred when user behaviour is studied in more details. Our work leads to clear recommendations on the design of immersive simulations for the study of crowd behavior.

Locomotion Techniques for Dynamic Environments: Effects on Spatial Knowledge and User Experiences

Various locomotion techniques are used to navigate and find way through space in virtual environments (VE), and each technique provides different experiences and performances to users. Previous studies have primarily focused on static environments, whereas there is a need for research from a different perspective of dynamic environments because there are many moving objects in VE, such as other users. In this study, we compare the effects of different locomotion techniques on the user's spatial knowledge and experience, depending on whether the virtual objects are moving or not. The investigated locomotion techniques include joystick, teleportation, and redirected walking (RDW), all commonly used for VR navigation. The results showed that the differences in spatial knowledge and user experience provided by different locomotion techniques can vary depending on whether the environment is static or dynamic. Our results also showed that for a given VE, there are different locomotion techniques that induce fewer collisions between the user and other objects, or reduce the time it takes the user to perform a given task. This study suggests that when designing a locomotion interface for a specific VR application, it is possible to improve the user's spatial knowledge and experience by recommending different locomotion techniques depending on the degree of environment dynamism and and type of task.

Crowd Navigation in VR: Exploring Haptic Rendering of Collisions

Virtual reality (VR) is a valuable experimental tool for studying human movement, including the analysis of interactions during locomotion tasks for developing crowd simulation algorithms. However, these studies are generally limited to distant interactions in crowds, due to the difficulty of rendering realistic sensations of collisions in VR. In this article, we explore the use of wearable haptics to render contacts during virtual crowd navigation. We focus on the behavioral changes occurring with or without haptic rendering during a navigation task in a dense crowd, as well as on potential after-effects introduced by the use haptic rendering. Our objective is to provide recommendations for designing VR setup to study crowd navigation behavior. To the end, we designed an experiment (N=23) where participants navigated in a crowded virtual train station without, then with, and then again without haptic feedback of their collisions with virtual characters. Results show that providing haptic feedback improved the overall realism of the interaction, as participants more actively avoided collisions. We also noticed a significant after-effect in the users' behavior when haptic rendering was once again disabled in the third part of the experiment. Nonetheless, haptic feedback did not have any significant impact on the users' sense of presence and embodiment.

A Fully-Immersive Virtual Reality Setup to Study Gait Modulation

Objective: Gait adaptation to environmental challenges is fundamental for independent and safe community ambulation. The possibility of precisely studying gait modulation using standardized protocols of gait analysis closely resembling everyday life scenarios is still an unmet need.

Methods: We have developed a fully-immersive virtual reality (VR) environment where subjects have to adjust their walking pattern to avoid collision with a virtual agent (VA) crossing their gait trajectory. We collected kinematic data of 12 healthy young subjects walking in real world (RW) and in the VR environment, both with (VR/A+) and without (VR/A-) the VA perturbation. The VR environment closely resembled the RW scenario of the gait laboratory. To ensure standardization of the obstacle presentation the starting time speed and trajectory of the VA were defined using the kinematics of the participant as detected online during each walking trial.

Results: We did not observe kinematic differences between walking in RW and VR/A-, suggesting that our VR environment per se might not induce significant changes in the locomotor pattern. When facing the VA all subjects consistently reduced stride length and velocity while increasing stride duration. Trunk inclination and mediolateral trajectory deviation also facilitated avoidance of the obstacle.

Conclusions: This proof-of-concept study shows that our VR/A+ paradigm effectively induced a timely gait modulation in a standardized immersive and realistic scenario. This protocol could be a powerful research tool to study gait modulation and its derangements in relation to aging and clinical conditions.

Technologies for Multimodal Interaction in Extended Reality—A Scoping Review

When designing extended reality (XR) applications, it is important to consider multimodal interaction techniques, which employ several human senses simultaneously. Multimodal interaction can transform how people communicate remotely, practice for tasks, entertain themselves, process information visualizations, and make decisions based on the provided information. This scoping review summarized recent advances in multimodal interaction technologies for head-mounted display-based (HMD) XR systems. Our purpose was to provide a succinct, yet clear, insightful, and structured overview of emerging, underused multimodal technologies beyond standard video and audio for XR interaction, and to find research gaps. The review aimed to help XR practitioners to apply multimodal interaction techniques and interaction researchers to direct future efforts towards relevant issues on multimodal XR. We conclude with our perspective on promising research avenues for multimodal interaction technologies.

The Untapped Potential of Virtual Reality in Rehabilitation of Balance and Gait in Neurological Disorders

Dynamic systems theory transformed our understanding of motor control by recognizing the continual interaction between the organism and the environment. Movement could no longer be visualized simply as a response to a pattern of stimuli or as a demonstration of prior intent; movement is context dependent and is continuously reshaped by the ongoing dynamics of the world around us. Virtual reality is one methodological variable that allows us to control and manipulate that environmental context. A large body of literature exists to support the impact of visual flow, visual conditions, and visual perception on the planning and execution of movement. In rehabilitative practice, however, this technology has been employed mostly as a tool for motivation and enjoyment of physical exercise. The opportunity to modulate motor behavior through the parameters of the virtual world is often ignored in practice. In this article we present the results of experiments from our laboratories and from others demonstrating that presenting particular characteristics of the virtual world through different sensory modalities will modify balance and locomotor behavior. We will discuss how movement in the virtual world opens a window into the motor planning processes and informs us about the relative weighting of visual and somatosensory signals. Finally, we discuss how these findings should influence future treatment design.

Motor adaptation to real-life external environments using immersive virtual reality: A pilot study

INTRODUCTION

Virtual reality (VR) has been described as an emerging therapeutic strategy to promote motor adaptation in different populations. The aim of this study was to investigate the effect of virtual environment demands, provided by an immersive VR system, on kinematic and spatio-temporal gait parameters in healthy young participants.

METHODS

Fifteen healthy young participants participated in this experimental study performing, in sequence, a baseline natural walking (NW) block, two different virtual environment walking blocks (snowy and crowded conditions), and a mixed walking block (including NW, snowy, and crowded conditions). Participants' Center-of-Mass (COM) excursion angle, medio-lateral (ML) COM excursion, step length, and walking speed were analyzed for each trial.

RESULTS

COM excursion angle and ML-COM excursion increased significantly during the first snowy and crowded VR trials compared to NW trials, while walking speed and step length decreased only for the snowy conditions. COM excursion angle and ML-COM excursion increased significantly from the first to the fourth VR snowy trial and decreased from the first to the fourth VR crowded trial. Participants retained the acquired motor adaptations even after the mixed block.

CONCLUSION

This study showed that kinematic and spatio-temporal gait parameters of young participants changed according to the virtual environment demands provided for each virtual scenario. In addition, all participants showed a consistent gait adaptation process to each virtual environment across the VR trials. The present findings highlight the impact of VR for gait adaptation, suggesting that VR training could modify motor behavior and enhance the motor adaptation process in healthy young participants.

Influence of path curvature on collision avoidance behaviour between two walkers

Navigating crowded community spaces requires interactions with pedestrians that follow rectilinear and curvilinear trajectories. In the case of rectilinear trajectories, it has been shown that the perceived action opportunities of the walkers might be afforded based on a future distance of closest approach. However, little is known about collision avoidance behaviours when avoiding walkers that follow curvilinear trajectories. Twenty-two participants were immersed in a virtual environment and avoided a virtual human (VH) that followed either a rectilinear path or a curvilinear path with a 5 m or 10 m radius curve at various distances of closest approach. Compared to a rectilinear path (control condition), the curvilinear path with a 5 m radius yielded more collisions when the VH approached from behind the participant and more inversions when the VH approached from in-front. During each trial, the evolution of the future distance of closest approach showed similarities between rectilinear paths and curvilinear paths with a 10 m radius curve. Overall, with few collisions and few inversions of crossing order, we can conclude that participants were capable of predicting future distance of closest approach of virtual walkers that followed curvilinear trajectories. The task was solved with similar avoidance adaptations to those observed for rectilinear interactions. These findings should inform future endeavors to further understand collision avoidance strategies and the role of-for example-non-constant velocities.

Evaluating Human Movement Coordination During Immersive Walking in a Virtual Crowd

This paper describes our investigation on how participants coordinate movement behavior in relation to a virtual crowd that surrounds them while immersed in a virtual environment. The participants were immersed in a virtual metropolitan city and were instructed to cross the road and reach the opposite sidewalk. The participants performed the task ten times. The virtual crowd that surrounded them was scripted to move in the same direction. During the experiment, several measurements were obtained to evaluate human movement coordination. Moreover, the time and direction in which the participants started moving toward the opposite sidewalk were also captured. These data were later used to initialize the parameters of simulated characters that were scripted to become part of the virtual crowd. Measurements were extracted from the simulated characters and used as a baseline to evaluate the movement coordination of the participants. By analyzing the data, significant differences between the movement behaviors of the participants and the simulated characters were found. However, simple linear regression analyses indicated that the movement behavior of participants was moderately associated with the simulated characters' movements when performing a locomotive task within a virtual crowd population. This study can be considered as a baseline for further research that evaluates the movement coordination of participants during human-virtual-crowd interactions using measurements obtained by the simulated characters.

Are avatars treated like human obstacles during aperture crossing in virtual environments?

RESEARCH OBJECTIVE

The current study set out to determine whether individuals walking in a virtual reality environment pass through apertures made of two avatars differently than apertures created by two pole obstacles, as previously observed between pole and human obstacles in real-world environments.

METHODS

Eleven healthy young adults wore a head-mounted virtual reality display, walked along a 10 m path and passed through a virtual aperture located 5 m from the starting location. Participants were instructed to avoid colliding with the obstacles when passing through the aperture. The experiment was conducted in a block design, where the aperture was either created by two pole obstacles or by two avatars. In both conditions, the width of the aperture ranged between 1.0-1.8x each participant's shoulder width.

RESULTS

Regardless of whether the aperture was created by the virtual poles or the avatars, participants rotated their shoulders for all aperture sizes and results found no significant differences in shoulder rotation angle, onset of rotation, walking speed or velocity at time of crossing between the two types of obstacles. Therefore, it appears that the differences in avoidance behaviours observed in real-world settings between people and pole obstacles is not translated to a virtual reality environment.

SIGNIFICANCE

It is possible that during experiments in which the avatars do not move, they do not possess human-like qualities suggested to be responsible for the increased caution used when walking through real human obstacles and instead, are treated as any ordinary obstacle.

Gait coordination in overground walking with a virtual reality avatar

Little information is currently available on interpersonal gait synchronization in overground walking. This is caused by difficulties in continuous gait monitoring over many steps while ensuring repeatability of experimental conditions. These challenges could be overcome by using immersive virtual reality (VR), assuming it offers ecological validity. To this end, this study provides some of the first evidence of gait coordination patterns for overground walking dyads in VR. Six subjects covered the total distance of 27 km while walking with a pacer. The pacer was either a real human subject or their anatomically and biomechanically representative VR avatar driven by an artificial intelligence algorithm. Side-by-side and front-to-back arrangements were tested without and with the instruction to synchronize steps. Little evidence of spontaneous gait coordination was found in both visual conditions, but persistent gait coordination patterns were found in the case of intentional synchronization. Front-to-back rather than side-by-side arrangement consistently yielded in the latter case higher mean synchronization strength index. Although the mean magnitude of synchronization strength index was overall comparable in both visual conditions when walking under the instruction to synchronize steps, quantitative and qualitative differences were found which might be associated with common limitations of VR solutions.

Detection of deceptive motions in rugby from visual motion cues

Frequently, in rugby, players incorporate deceptive motions (e.g., a side-step) in order to pass their opponent. Previous works showed that expert defenders are more efficient in detecting deceptive motions. Performance was shown to be correlated with the evolution of the center of gravity of the attacker, suggesting that experts may rely on global motion cues. This study aims at investigating whether a representation of center of gravity can be useful for training purposes, by using this representation alone or by combining it with the local motion cues given by body parts. We designed an experiment in virtual reality to control the motion cues available to the defenders. Sixteen healthy participants (seven experts and nine novices) acted as defenders while a virtual attacker approached. Participants completed two separate tasks. The first was a time occlusion perception task, occlusion after 100ms, 200ms or 300ms after the initial change in direction, thereafter participants indicated the passing direction of the attacker. The second was a perception-action task, participants were instructed to intercept the oncoming attacker by displacing medio-laterally. The attacker performed either a non-deceptive motion, directly toward the final passing direction or a deceptive motion, initially toward a false direction before quickly reorienting to the true direction. There was a main effect of expertise, appearance, cut off times and motion on correct responses during both tasks. There was an interaction between visual appearance and expertise, and between motion type and expertise during the perception task, however, this interaction was not present during the perception-action task. We observed that experts maintained superiority in the perception of deceptive motion; however when the visual appearance is reduced to global motion alone the difference between novices and experts is reduced. We further explore the interactions and discuss the effects observed for the visual appearance and expertise.

Interpersonal Affordances and Social Dynamics in Collaborative Immersive Virtual Environments: Passing Together Through Apertures

An essential question in understanding how to develop and build collaborative immersive virtual environments (IVEs) is recognizing how people perform actions together. Many actions in the real world require that people act without prior planning, and these actions are executed quite successfully. In this paper, we study the common action of two people passing through an aperture together in both the real world (Experiment 1) and in a distributed, collaborative IVE (Experiment 2). The aperture's width is varied from too narrow to be passable to so wide as to be easily passable by both participants together simultaneously. We do this in the real world for all possible gender-based pairings. In virtual reality, however, there is potential for the gender of the participant and the gender of the self-avatar to be different. We also investigate the joint action for all possible gender-based pairings in the distributed IVE. Results indicated that, in the real world, social dynamics between gendered pairings emerged; male-male pairings refused to concede to one another until absolutely necessary while other pairings did not. Male-female pairings were most likely to provide ample space to one another during passage. These behaviors seemed not to appear in the IVE, and avatar gender across all pairings generated no significant behavioral differences. In addition, participants tended to require wider gaps to allow for passage in the IVE. These findings establish base knowledge of social dynamics and affordance behaviors within multi-user IVEs.

Walking with avatars: Gait-related visual information for following a virtual leader

Dynamic situations, such as interactive sports or walking on a busy street, impose high demands on a person's ability to interact with (others in) its environment (i.e., 'interact-ability'). The current study examined how distance regulation, a fundamental component of these interactions, is mediated by different sources of visual information. Participants were presented with a back and forwards moving virtual leader, which they had to follow by walking back and forwards themselves. We presented the leader in several appearances that differed in the presence of segmental (i.e., relative movements of body segments), cadence-related (i.e., sway and bounce), and global (i.e., optical expansion-compression) information. Results indicated that removing segmental motion information from the virtual leader significantly deteriorated both temporal synchronization and spatial accuracy of the follower to the leader, especially when the movement path of the leader was less regular/predictable. However, no difference was found between cadence-related and global motion information appearances. We argue that regulating distance with others effectively requires a versatile attunement to segmental and global motion information depending on the specific task demands. The results further support the notion that detection of especially segmental information allows for more timely 'anticipatory' tuning to another person's locomotor movements and intentions.

Guided by gaze: Prioritization strategy when navigating through a virtual crowd can be assessed through gaze activity

Modelling crowd behavior is essential for the management of mass events and pedestrian traffic. Current microscopic approaches consider the individual's behavior to predict the effect of individual actions in local interactions on the collective scale of the crowd motion. Recent developments in the use of virtual reality as an experimental tool have offered an opportunity to extend the understanding of these interactions in controlled and repeatable settings. Nevertheless, based on kinematics alone, it remains difficult to tease out how these interactions unfold. Therefore, we tested the hypothesis that gaze activity provides additional information about pedestrian interactions. Using an eye tracker, we recorded the participant's gaze behavior whilst navigating through a virtual crowd. Results revealed that gaze was consistently attracted to virtual walkers with the smallest values of distance at closest approach (DCA) and time to closest approach (TtCA), indicating a higher risk of collision. Moreover, virtual walkers gazed upon before an avoidance maneuver was initiated had a high risk of collision and were typically avoided in the subsequent avoidance maneuver. We argue that humans navigate through crowds by selecting only few interactions and that gaze reveals how a walker prioritizes these interactions. Moreover, we pose that combining kinematic and gaze data provides new opportunities for studying how interactions are selected by pedestrians walking through crowded dynamic environments.

Circumvention of Pedestrians While Walking in Virtual and Physical Environments

Virtual environments (VEs) are increasingly used in the context of scientific inquiries and rehabilitation for tasks that are otherwise difficult to control or perform safely in physical environments (PEs), such as avoiding other pedestrians during locomotion. The usefulness of VEs, however, remains constrained by the extent to which they can elicit natural responses. The objectives of the study were to examine circumvention strategies in response to pedestrians approaching from different directions in the VE versus PE and to determine the effects of repeated practice on the circumvention strategies. Twelve participants were assessed over five blocks of eight trials that consisted of walking toward a target while circumventing pedestrians approaching from different directions (0°, ± 30° right or left or none) in the VE and the PE. Similar onset distances of circumvention strategy and preferred side of circumvention were observed between the two environments. Participants, however, maintained enlarged minimum distances from the interferer (13%) and walked slower (11.5%) in the VE. Repeated practice resulted in walking speed increments of 7.4% over the entire session that were similar in the VE versus PE. While the changes observed in VE may reflect the use of more cautious circumvention strategies, the similarities in strategies between the two environments and the advantages of VEs (e.g., controlled exposure, reproduction of ecologically valid conditions, and safety) suggest that virtual reality is a valuable tool to study visually guided locomotor tasks, such as pedestrian circumvention, and shows great potential for assessment and intervention in physical rehabilitation.