Cybersickness without the wobble Mark Dennison Department of Cognitive Sciences University of California, Irvine November 18, 2015

What is cybersickness? Cybersickness is a type of motion sickness felt during immersion in virtual reality (VR) Symptoms include: nausea, vomiting, facial pallor, increased body temperature, salivation, headache1,2,3,4 The underlying causes of this sickness are still not agreed upon 1) Money, 1970; 2) Reason, 1978; 3) Treisman, 1977; 4) Yates et al., 1998a

Sensory Mismatch Theory Motion sickness caused by conflicting information between the visual, vestibular, and proprioceptive systems5,6 Severity of symptoms increase with amount of mismatch between actual signals and what is expected e.g. Moving an avatar in virtual reality (VR) while remaining stationary in reality7 5) Reason and Brand, 1975; 6) Reason, 1978, 7) Dennison et al. (submitted)

Postural Instability Theory8,9 Suggests that cybersickness is not caused by conflicting sensory information Control of body stability and sense of gravity are necessary for normal function Claim cybersickness is preceded by postural instability due to lack of an appropriate body control scheme This theory makes sense when considering microgravity and some theme park attractions 8) Riccio & Stoffregen (1988); 9) Riccio & Stoffregen (1991); https://www.youtube.com/watch?v=pjdVLRyTrZw

Aim: Test Postural Instability Theory in VR Create a visually unstable environment by replicating Dichgans and colleagues (1972) experiment on the perceived direction of gravity Rebecca Chen I was helped in early phases of this work by UCI alumn Rebecca Chen, who was a Psych honors student in our lab at the time

Perceived Direction of Gravity Subjects in the 1972 study viewed monocularly a 2D dot field (130 deg diameter) that rotated about the line of sight Subjects rotated an arrow to match the perceived vertical The tilt of the perceived vertical increased with rotation speed The direction of the tilt matched the direction of the rotation Dichgans, Held, Young and Brandt (1972) Dichgans and colleagues (1972)

Aim: Test Postural Instability Theory in VR Create a visually unstable environment by replicating Dichgans and colleagues (1972) experiment on the perceived direction of gravity Two sessions: seated and standing Measure changes in postural stability and cybersickness So we brought subjects in for two sessions to measure changes in postural stability and cybersickness Wii Balance Board Oculus Rift Dev Kit 2

Aim: Test Postural Instability Theory in VR Create a visually unstable environment by replicating Dichgans and colleagues (1972) experiment on the perceived direction of gravity Two sessions: seated and standing Measure changes in postural stability and cybersickness Hypotheses: cybersickness will increase with rotation speed (as in the Dichgans study) and will be greater while standing than while seated Our hypothesis, assuming postural instability theory is true, is that cybersickness…

Aim: Test Postural Instability Theory in VR We rotated the virtual tunnel clockwise and counter-clockwise Six rotation speeds ranged from 6 to 60 deg/s Each trial lasted 30 seconds (4 trials per condition, 48 trials per session) Measurements: perceived vertical offsets, cybersickness, and response time posture using a Wii balance board (weights measured by four sensors) head position from the HMD Subjects (N = 15) filled out Simulator Sickness Questionnaire (SSQ) at end of session So for our study we rotated…

Perceived Vertical Offsets Offsets tilt in the direction of tunnel rotation Offsets do not increase with rotation speed Offsets do not depend on seated vs. standing viewing We partially replicated Dicgans. Point at statistical insignificance of 2 an 3. F(1,13) = 2.296, p < .000

Cybersickness Increases with Rotation Speed Cybersickness increases with speed for both seated and standing conditions Cybersickness is unrelated to perceived vertical settings Cybersickness at the two fastest speeds is positively correlated with end-of-experiment SSQ scores F(1.4,17.5) = 5.051, p < .029 1 = no symptoms, 2 = some symptoms, 3 = mild nausea, 4 = moderate nausea (The majority of subjects reported a 2 or higher on at least one trial)

Response Times Response times do not depend on rotation speed Response times do not depend on seated vs standing This suggests that motion aftereffects from previous trials do not influence perceived vertical settings

Interim Conclusions Perceived vertical offsets are tilted in the direction of tunnel rotation, which agrees with results of Dichgans and colleagues Perceived vertical offsets do not depend on rotation speed, which disagrees (smaller FOV, interleaved speeds) Increasing rotation speed increases cybersickness Cybersickness increases similarly for seated and standing subjects … but what about the wobble?

Forward-Backward Postural Change at Stimulus Rotation Onset (for the Minority) Sample FB data from a representative subject who wobbles Only three subjects showed such a response There were no notable changes in the Right-Left direction Data are from the two fastest speeds

Forward-Backward Postural Change at Stimulus Rotation Onset (for the Majority) 11 of 14 subjects showed no appreciable wobble in their posture after rotation onset There were no notable changes in the Right-Left direction For the majority, cybersickness is not accompanied by wobble Same axes as previous slide for ease of comparison

Less Comfortable Subjects Wobbled Less Split subjects into two groups using SSQ score: More Comfortable and Less Comfortable The plotted variations at right are the standard deviations of the posture time series10 FB posture variation is greater for More Comfortable subjects These data speak against postural instability theory 10) Koslucher et al. (2012)

Less Comfortable Subjects Wobbled Less Split subjects into two groups using SSQ score: More Comfortable and Less Comfortable The plotted variations at right are the standard deviations of the posture time series1 FB posture variation is greater for More Comfortable subjects These data speak against postural instability theory The body is not wobbling as expected by Postural Instability Theory. We have not shown this for the head, which is where the vestibular system’s semicircular canals and otolith organs are located. How are body posture and head position related in this experiment?

Forward-Backward Head and Body Movements are Closely Coupled Head position and body posture were cross-correlated on each trial 95% confidence intervals were calculated by correlating head and body data on unmatched trials11 Movements of the head closely match movements of the body in the FB direction only * We saw that peopled wobbled in the FB direction, which agrees with earlier results, despite this being counter intuitive lags separated by 0.01s from -30 to 30 sec FB = forward-backward RL = right-left Data from a representative subject 11) Horton et al. (2013)

Conclusions Future Work Cybersickness increased as stimulus rotation speed increased. There was no corresponding increase in perceived vertical offset. This suggests that cybersickness and perceived vertical are not correlated. Postural instability theory fails to explain the similar levels of cybersickness experienced by seated and standing subjects. Subjects who experience more cybersickness exhibit less postural instability. The lesser postural change in less comfortable subjects may be related to a phenomenon I call “VR lock”; subjects who feel sick keep their head and body immobile. Future Work How does cybersickness evolve over time? Can physiological data be used to estimate cybersickness in individual subjects?

Thank you! And thanks to: Rebecca Chen Mike D’Zmura Jonathan Kasko Stacie Sanchez Zack Wisti