The influence of gravitoinertial force level on oculomotor and perceptual responses to Coriolis, cross-coupling stimulation.

Susceptibility to motion sickness during exposure to constant levels of Coriolis, cross-coupling stimulation is lower in zero G and higher in 1.8 G than in a 1-G force environment (10, 13). The goal of the present experiment was to determine whether gravitoinertial force magnitude also influences oculomotor and perceptual responses to Coriolis, cross-coupling stimulation. We had blind-folded subjects who were rotating at constant velocity make standardized head movements during the free-fall and high force phases of parabolic flight, and we measured both the characteristics of their horizontal nystagmus and the magnitude of their experienced self-motion. Both responses were less intense in the free-fall periods than in the high force periods. Although the slow phase velocity of nystagmus reached the same initial, peak level in both conditions, it decayed more quickly in zero G. These findings suggest that the response to semicircular canal stimulation depends on the background level of gravitoinertial force.