Postural instability and motion sickness in a fixed-base flight simulator

We evaluated the prediction that postural instability would precede the sub jective symptoms of motion sickness in a fixed-base flight simulator: Parti cipants sat in a cockpit in a video projection dome and were exposed to opt ical flow that oscillated in the roll axis with exposure durations typical of flight simulation. The frequencies of oscillation were those that charac terize spontaneous postural sway during stance. Head motion was measured pr ior to and during exposure to imposed optical flow. Of 14 participants, 6 w ere classified as motion sick, either during or after exposure to the optic al oscillation. Prior to the onset of subjective symptoms, head motion amon g participants who later became sick was significantly greater than among p articipants who did not become motion sick. We argue that the results suppo rt the postural instability theory of motion sickness. Actual or potential applications include the prevention ol mitigation of motion sickness in vir tual environments.