Expanding and contracting optical flow patterns and simulator sickness.

Background: Sensory conflict may be a factor in simulator sickness (SS) given that visual input is often inconsistent with other sensory inputs. It was predicted that an expanding optical flow pattern would lead to more sensory conflict, and subsequently more SS than a contracting pattern.

Methods: There were 16 individuals who participated in the experiment (6 men, 10 women, mean age = 24.4 yrs). Subjects viewed a steadily expanding pattern of blue squares displayed on a computer monitor. In a second condition the pattern steadily contracted. Subjects completed the Simulator Sickness Questionnaire (SSQ) designed by Kennedy and colleagues both before and after a trial (5 min exposure to optic flow). A total SSQ score and three SSQ sub-scores (nausea, oculomotor, and disorientation) were obtained.

Results: Mean post-treatment total SSQ scores (mean=28) in the expanding condition were higher than those obtained in the contracting condition (mean=17). Nausea and oculomotor SSQ sub-scores were also higher in the expanding condition compared with the contracting condition.

Conclusions: Experience with expanding flow patterns that result during forward self-motion, and the sensory inputs that usually accompany them, have resulted in a central nervous system expectancy about what the appropriate inputs should be during forward self-motion. Less experience with backwards self-motion (and contracting patterns) may result in a lower level of expectation regarding what the appropriate sensory inputs should be for contracting flow patterns. This lower level of neural expectancy may subsequently lead to less sensory conflict and less SS generated by contracting flow patterns.