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

2. 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

3. 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)

4. 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);

5. 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

6. 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)

7. 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

8. 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…

9. 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…

10. 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

11. 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)

12. 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

13. 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?

14. 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

15. 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

16. 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)

17. 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?

18. 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)

19. 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?

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