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 sensoryinputs. It was predicted that an expanding optical flow pattern wouldlead to more sensory conflict, and subsequently more SS than a contractingpattern. Methods: There were 16 individuals who participatedin the experiment (6 men, 10 women, mean age 24.4 yrs). Subjectsviewed a steadily expanding pattern of blue squares displayed on acomputer monitor. In a second condition the pattern steadily contracted.Subjects completed the Simulator Sickness Questionnaire (SSQ) designedby Kennedy and colleagues both before and after a trial (5 minexposure to optic flow). A total SSQ score and three SSQ sub-scores(nausea, oculomotor, and disorientation) were obtained. Results: Meanpost-treatment total SSQ scores (mean 28) in the expanding conditionwere higher than those obtained in the contracting condition (mean 17). Nausea and oculomotor SSQ sub-scores were also higher in theexpanding condition compared with the contracting condition. Conclusions:Experience with expanding flow patterns that result during forwardself-motion, and the sensory inputs that usually accompany them,have resulted in a central nervous system expectancy about what theappropriate inputs should be during forward self-motion. Less experiencewith backwards self-motion (and contracting patterns) may resultin a lower level of expectation regarding what the appropriate sensoryinputs should be for contracting flow patterns. This lower level of neuralexpectancy may subsequently lead to less sensory conflict and less SSgenerated by contracting flow patterns.