Improvement of Redirected Walking in Virtual Reality: Optical Flow Modulation, Multi-sensory Stimulation, and Interactive User Behavior

Abstract

The study focuses on the implementation of redirected walking (RDW) technology in virtual reality (VR) environments. RDW, a software-based VR locomotion technology, enables users to navigate large virtual spaces beyond physical limits by manipulating their perception of motion. Unlike real-world locomotion, RDW controls virtual scenes differently, providing users with a seamless and natural walking experience within confined tracking areas. However, this technique inevitably causes a visual-vestibular discrepancy. If users become consciously aware of this visual-vestibular discrepancy, it can lead to a phenomenon known as "semantic violation." The detection of such discrepancies disrupts users' presence in the VR environment, often resulting in discomfort and symptoms like motion sickness. The "detection threshold" (DT) is pivotal in this relationship, representing the point at which users cannot perceive a perceptual discrepancy, ensuring their immersive VR experience. On the other hand, the effectiveness of RDW faces challenging constraints caused by the DT, limiting users to virtual areas and necessitating frequent redirection interventions, thus impacting the overall user experience. Consequently, there is a need to extend the DT. This study aims to achieve three goals: enhancing redirection performance, reducing user discomfort, and understanding the user’s perception of redirection. To accomplish these goals, four methods have been proposed. These four methods are devised with the goal of examining the possibility of extending the DT and mitigating discomfort by modulating user awareness of redirection manipulation. One technique involves optical flow (OF) modulation, manipulating the OF direction in virtual space. Results indicate that redirection performance improves when the OF is presented opposite to the actual movement of VR-familiar users. This suggests that VR-familiar users are more attentive to OF-generating effects than relatively unfamiliar users, thereby increasing redirection performance. To apply these results effectively, incorporating visual effects tailored to the VR context, such as trees swaying or animated characters, may be beneficial. The study also explores auditory and olfactory stimuli for redirecting users. Olfactory cues increase the angle of reorientation, while auditory cues decrease the time required to reorient. The combination of olfactory and auditory stimuli enhances reorientation performance, even with frequent presentation. However, addressing the disadvantage of requiring additional equipment and olfactory materials is essential. Another aspect of the study involves providing vestibular sensory stimulation. Electrical-based methods effectively increase gait stability and reduce discomfort, while the non-electrical method (i.e., Bone-Conduction Vibration) induces task performance enough to play in gaming scenarios requiring frequent changes of direction. Combining non-electrical stimuli with background music or sound effects can provide vestibular stimulation without a tailored scenario. Nevertheless, employing a vestibular stimulation system has the potential to cause discomfort for users. The study investigates the effectiveness of RDW technology in interactive user behavior tasks. Results indicate that users are less likely to perceive RDW technology use during such tasks, especially in situations with limited viewing distance or tasks requiring object handling. Focusing the user's visual attention on interactive elements could enhance redirection performance. Despite the potential implementation of RDW technology in pre-designed VR interaction scenarios, the challenge of addressing scenario diversity persists and requires a solution. The study provides design guidelines for integrating RDW technology into VR content. To effectively incorporate these results, designers should consider the VR context, sensory-vestibular stimulation, and tasks requiring interactive user behavior in the design stage. It is crucial to provide these techniques only when users can appropriately accept and engage with them. Identifying the user's physical and cognitive state using mixed sensors enables the natural building of VR content and suitable usage of RDW technology. The outcome aims to simulate movement in a virtual space exceeding physical limitations without degrading the VR user experience.