Introduction: Off-vertical axis rotation (OVAR) provokes motion sickness. The visual motion equivalent to OVAR in simulators is also nauseogenic. Our experiment compared the nauseogenicity of OVAR vs. visual motion.
Methods: There were 12 subjects who undertook the following conditions: A) OVAR in darkness at 0.2 Hz, 18 degrees tilt; B) same OVAR with eyes open in the light; and C) stationary, seated upright, watching a video of the visual motion experienced in B. The conditions were counterbalanced and performed at the same time of day with a minimum 5-d separation between conditions. Stimulation was stopped at moderate nausea with a 20-min maximum cut-off. Motion sickness susceptibility was rated on a standardized questionnaire (MSSQ).
Results: Time (mean +/- SD minutes) to moderate nausea was significantly shorter for real OVAR conditions (A: 7.1 +/- 5.5; B: 7.7 +/- 6.7) vs. video (C: 15.7 +/- 6.4). Subjects with relatively low susceptibilities to motion sickness developed nausea more slowly with vision (B-A time difference correlated with MSSQ scores r = -0.7, P < 0.05). Headache was more prominent with visual field motion (C).
Conclusions: OVAR was twice as nauseogenic as visual motion. Headache during visual motion suggests mechanisms in common with migraine. We hypothesize that subjects who fared better in the light used visual cues to resolve sensory conflict, whereas subjects who were equally susceptible in light and dark made poor use of visual cues; perhaps a form of 'field dependency'. This may explain why some people prefer 'a view of the road ahead' to help against motion sickness whereas others shut their eyes.