Visually induced motion sickness with radial displays: Effects of gaze angle and fixation

Background: Exposure to moving visual scenes can induce illusory feelings of self-motion (vection) and visually induced motion sickness in stationary observers. We have investigated the effect of viewing conditions on motion sickness in a radial optic flow environment, simulating the situation in which an observer shifts gaze in order to sample from the environment. In view of the spatiotemporal structure of radial flow patterns, vection magnitude and motion sickness were expected to increase when gaze position was directed away from the focus of expansion. Methods: There were 12 participants who were exposed to an expanding-contracting radial optic flow pattern under four viewing conditions: 1) fixation at the focus of expansion; 2) fixation at targets located 16 degrees eccentric with respect to the focus of expansion; 3) consecutive gaze shifting between the focus of expansion and eccentric located targets; and 4) free viewing. Subjective measures of motion sickness and vection were obtained and gaze position was monitored using video-oculography. Results: Forced eccentric gaze position (conditions 2 and 3) significantly increased the level of motion sickness and facilitated vection. Mean accumulated sickness ratings in conditions 2 and 3 were about 20% higher than the conditions in which participants were free to move their eyes or were asked to fixate at the focus of expansion, and this trend was consistent across the different sickness measures employed. Conclusion: Optic flow appears to interact differently with different portions of the retina and, in central vision at least, visually induced motion sickness is influenced by retinal image velocity.