Testing the ‘differences in virtual and physical head pose’ and ‘subjective vertical conflict’ accounts of cybersickness

Abstract

AbstractWhen we move our head while in virtual reality, display lag will generate differences in our virtual and physical head pose (known as DVP). While DVP are a major trigger for cybersickness, theories differ as to exactly how they constitute a provocative sensory conflict. Here, we test two competing theories: the subjective vertical conflict theory and the DVP hypothesis. Thirty-two HMD users made continuous, oscillatory head rotations in either pitch or yaw while viewing a large virtual room. Additional display lag was applied selectively to the simulation about the same, or an orthogonal, axis to the instructed head rotation (generating Yaw-Lag + Yaw-Move, Yaw-Lag + Pitch-Move, Pitch-Lag + Yaw-Move, and Pitch-Lag + Pitch-Move conditions). At the end of each trial: (1) participants rated their sickness severity and scene instability; and (2) their head tracking data were used to estimate DVP throughout the trial. Consistent with our DVP hypothesis, but contrary to subjective vertical conflict theory, Yaw-Lag + Yaw-Move conditions induced significant cybersickness, which was similar in magnitude to that in the Pitch-Lag + Pitch-Move conditions. When extra lag was added along the same axis as the instructed head movement, DVP was found to predict 73–76% of the variance in sickness severity (with measures of the spatial magnitude and the temporal dynamics of the DVP both contributing significantly). Ratings of scene instability were also found to predict sickness severity. Taken together, these findings suggest that: (1) cybersickness can be predicted from objective estimates of the DVP; and (2) provocative stimuli for this sickness can be identified from subjective reports of scene instability.