The vestibulo-ocular reflex and seasickness susceptibility.

VOR parameters were compared in subjects at the extremes of the seasickness susceptibility scale. Thirty-nine subjects highly susceptible to seasickness and 30 nonsusceptible subjects participated in the study. The VOR was evaluated by the Sinusoidal Harmonic Acceleration (SHA) test at frequencies of 0.01, 0.02, 0.04, 0.08, and 0.16 Hz. In subjects susceptible to seasickness, VOR gain was significantly higher at 0.02 and 0.04 Hz, and phase lead was significantly lower at 0.01, 0.02, 0.04, and 0.08 Hz, than in nonsusceptible subjects. Our findings are in agreement with the notion that the vestibular response will be more intense in subjects susceptible to motion sickness. The present results support the contention that a natural insusceptibility, or increased resistance to seasickness produced by adaptive responses to repeated sea exposures, may be reflected by lower VOR gain and higher phase lead.