Design and Evaluation of Dynamic Field-of-View Restriction Techniques to Mitigate Cybersickness in Virtual Reality

Abstract

Although virtual reality has been gaining in popularity, users continue to report discomfort during and after the use of VR applications, and many experience symptoms associated with cybersickness. To mitigate this problem, dynamic field-of-view (FOV) restriction is a common technique that has been widely implemented in commercial VR games. FOV restriction artificially reduces the field of view during movement to limit optical flows and reduce discomfort caused by the mismatch between virtual motion and physical motion. FOV restriction has been shown in numerous studies to improve comfort and enhance user experience in virtual reality. The standard dynamic FOV restriction is created by adding a symmetrical black opaque mask at the periphery of the user’s filed-of-view and its size changes only with the user's virtual velocity. It does not take into account any differences in users, virtual environments, or other usage conditions. This simplistic implementation leads to some limitations. The first limitation is that the FOV restriction reduces users' visibility of the virtual environment and can negatively impact their subjective experience. The second limitation is that the unblocked imagery when applying restrictor is usually in the center of the field of view, which is incompatible with the users' eye movements during locomotion. The third limitation is that the classical restrictor is scaled by the velocity and angular velocity of users' virtual movements. This design assumes that users feel the same cybersickness when they experience the same velocity, which is unrealistic. Beyond these limitations, there is a lack of scientific understanding of how to effectively apply FOV restrictions for different types of virtual environments and virtual motions. This thesis presents four major contributions to the existing dynamic FOV restriction research. First, I present a novel technique known as passthrough FOV restriction, which combines the dynamic field of view modification with rest frames generated from 3D scans of the physical environment. The informal testing suggests that this approach is a promising method for reducing motion sickness and improving user safety at the same time. Secondly, I present a novel asymmetric field-of-view restrictor known as the ground-visible restrictor, which maintains the visibility of the ground plane during movement. User studies showed that ground-visible FOV restriction offers benefits for user comfort, postural stability, and a subjective sense of presence. Thirdly, I provide another variant of FOV restriction, referred to as the side restrictor, which expands side visibility and maintains restriction during rotation. A user study evaluated the new technology and demonstrated its benefits in reducing cybersickness and discomfort and improving visibility. Finally, I present an adaptive restrictor that uses the optical flow amount to determine the position and size of the restriction. A mixed design study investigated its performance and confirmed its superiority over traditional restrictors in providing a better subjective user experience.