Cybersickness remains a major barrier to the widespread adoption of virtual reality (VR) technologies, motivating researchers to investigate its causes and mitigation strategies through comparative human-subjects studies. These experiments may employ either within- or between-subjects designs. Although within-subjects designs require fewer participants and potentially offer higher statistical power, researchers need to wash out carryover effects of cybersickness symptoms before each session to avoid confounding the results. Prior studies have employed washout periods of varying lengths; some required testing conditions on different days, while others allowed only short breaks of less than 15 minutes. Although shorter washout periods are more convenient for experimenters, their impact on study outcomes has not been systematically investigated. In this work, we conducted a meta-analysis to evaluate the effects of study design and washout period length on cybersickness self-reports measured with the Simulator Sickness Questionnaire (SSQ). We found that short washout periods reduce statistical power compared to long washout periods or between-subjects designs. Based on these findings, we provide guidelines to help researchers design more reliable cybersickness studies and improve the generalizability of their results.

The decoupled relationship between the optical and inertial information in virtual reality is commonly acknowledged as a major factor contributing to cybersickness. Based on laws of physics, we noticed that a slope naturally affords acceleration, and the gravito-inertial force we experience when we are accelerating freely on a slope has the same relative direction and approximately the same magnitude as the gravity we experience when standing on the ground. This provides the opportunity to simulate a slope by manipulating the orientation of virtual objects accordingly with the accelerating optical flow. In this paper, we present a novel space deformation technique that deforms the virtual environment to replicate the structure of a slope when the user accelerates virtually. As a result, we can restore the physical relationship between the optical and inertial information available to the user. However, the changes to the geometry of the virtual environment during space deformation remain perceptible to users. Consequently, we created two different transition effects, pinch and tilt, which provide different visual experiences of ground bending. A human subject study (N=87) was conducted to evaluate the effects of space deformation on both slope perception and cyber-sickness. The results confirmed that the proposed technique created a strong feeling of traveling on a slope, but no significant differences were found on measures of discomfort and cybersickness.

Women are more likely to experience virtual reality (VR) sickness than men, which could pose a major challenge to the mass market success of VR. Because VR sickness often results from a visual-vestibular conflict, an effective strategy to mitigate conflict is to restrict the user’s field-of-view (FOV) during locomotion. Sex differences in spatial cognition have been well researched, with several studies reporting that men exhibit better spatial navigation performance in desktop three-dimensional environments than women. However, additional research suggests that this sex difference can be mitigated by providing a larger FOV as this increases the availability of landmarks, which women tend to rely on more than men. Though FOV restriction is already a widely used strategy for VR headsets to minimize VR sickness, it is currently not well understood if it impedes spatial learning in women due to decreased availability of landmarks. Our study (n=28, 14 men and 14 women) found that a dynamic FOV restrictor was equally effective in reducing VR sickness in both sexes, and no sex differences in VR sickness incidence were found. Our study did find a sex difference in spatial learning ability, but an FOV restrictor did not impede spatial learning in either sex.

Virtual reality sickness typically results from visual-vestibular conflict. Because self-motion from optical flow is driven most strongly by motion at the periphery of the retina, reducing the user’s field-of-view (FOV) during locomotion has proven to be an effective strategy to minimize visual vestibular conflict and VR sickness. Current FOV restrictor implementations reduce the user’s FOV by rendering a restrictor whose center is fixed at the center of the head mounted display (HMD), which is effective when the user’s eye gaze is aligned with head gaze. However, during eccentric eye gaze, users may look at the FOV restrictor itself, exposing them to peripheral optical flow which could lead to increased VR sickness. To address these limitations, we develop a foveated FOV restrictor and we explore the effect of dynamically moving the center of the FOV restrictor according to the user’s eye gaze position. We conducted a user study (n=22) where each participant uses a foveated FOV restrictor and a head-fixed FOV restrictor while navigating a virtual environment. We found no statistically significant difference in VR sickness measures or noticeability between both restrictors. However, there was a significant difference in eye gaze behavior, as measured by eye gaze dispersion, with the foveated FOV restrictor allowing participants to have a wider visual scan area compared to the head-fixed FOV restrictor, which confined their eye gaze to the center of the FOV.

Recent studies show that women are more susceptible to visually-induced VR sickness, which might explain the low adoption rate of VR technology among women. Reducing field-of-view (FOV) during locomotion is already a widely used strategy to reduce VR sickness as it blocks peripheral optical flow perception and mitigates visual/vestibular conflict. Prior studies show that men are more adept at 3D spatial navigation than women, though this sex bias can be minimized by providing women with a larger FOV. Our study provides insight into the relationship between sex and FOV restriction with respect to VR sickness and spatial navigation performance which seem to conflict. We find the use of an FOV restrictor to be effective in mitigating VR sickness in both sexes while we did not find a negative effect of FOV restriction on spatial navigation performance.