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Thesis

Vestibulo-Ocular Reflex Adaptation and Motion Sickness Symptoms in Response to Virtual Reality Exposure

19 June 2020

Abstract

Significance: VOR adaptation as a predictor of cybersickness symptoms would elucidate the physiological mechanism by which sensory conflicts are able to induce these symptoms. This can be used to reduce symptoms in those at a higher risk with individually based modification of content and to provide an objective for future therapeutic approaches. The long-term goal of this research is to increase user comfort and reduce negative side effects of virtual reality, in order for VR technology to be accessible to the entire population.

Purpose: Many users of virtual reality (VR) devices experience severe discomfort after even just a few minutes, reporting symptoms including nausea, headache, and eyestrain. These symptoms are commonly referred to as cybersickness, and are thought to be from conflicting visual, vestibular, and proprioceptive signals. Vestibulo-Ocular Reflex (VOR) is likely a primary source of such conflict and can adapt to reduce associated symptoms with accrued experiences. The present study examined if the amplitude or rate of vision-enhanced and vision-denied VOR gain adaptation can predict the susceptibility and mitigation of cybersickness symptoms over time.

Specific Aims: Our aims are to (1) develop a method for assessing the VOR during VR use utilizing a head-mounted virtual reality display in conjunction eye/head-tracking goggles, (2) explore VOR and VVOR adaptation amplitude and rate during exposure to various virtual conditions, and (3) relate VOR adaptation to symptom scores

Methods: Thirty-six participants played a custom VR game requiring horizontal head rotation. The gain of updated visual shift in relation to the demand of head rotation was manipulated to be 50, 100 (control) and 200% of predicted visual shift. An Oculus Rift headset rendered the visual input and an integrated eye tracking system monitored the head rotation velocity and gaze position relative to the head. Participants’ long-term and pre-game cybersickness propensity were assessed with the Motion Sickness Assessment Questionnaire (MSAQ), and their momentary discomfort measured with an analog scale every minute.

Results: Individuals with higher motion sickness symptoms exhibited significantly less adaptation of the VOR to the imposed visual shifts. The control condition induced an increase in VOR gain for all participants; individuals with high nausea on the control condition had significantly increased VOR responses relative to those with low symptoms. Adaptation to the 50% condition took longer and was more nausea-inducing than the 200% or control conditions. Additionally, individuals with decreased stereoacuity (25 arcsec or worse) had higher symptoms than individuals with excellent stereoacuity (20 arcsec).

Conclusions: Despite recent technological advances, virtual reality head-mounted displays still cause transient vestibulo-ocular reflex changes that result in motion sickness symptoms. This is especially evident when the content imposes an adaptation requirement to a decreased rotational gain demand. Even without imposing an intentional demand, the 1X (Control) condition resulted in a variety of VVOR/VOR adaptation responses. Researchers, device manufacturers, and content developers should explore utilizing objective and/or subjective methods to personalize the display responses to rotational position changes in an effort to reduce visual-vestibular conflict and ameliorate symptoms.

Keywords: Vestibulo-Ocular Reflex Adaptation, Stereoacuity, Virtual Reality, Motion Sickness, Cybersickness

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