Modification of Vestibular Responses as a Function of Rate of Rotation About an Earth-Horizontal Axis

Eight men completed an experiment in which they were rotated about an Earth-horizontal axis at velocities of 10 and 30 rpm. Both nystagmus and subjective estimates of body position in space were modified by the higher rate of rotation. Subjects who gave essentially veridical estimates of body position at 10 rpm became disoriented at 30 rpm and gave responses closely resembling those of subjects with labyrinthine dysfunction. Subjects who produced sustained unidirectional horizontal nystagmus during constant velocity rotation at 10 rpm produced a reversing horizontal nystagmus during comparable intervals of rotation at 30 rpm. Nystagmus slow phase velocity for both 10 and 30 rpm exhibited a cyclic modulation which was related to orientation relative to gravity. As in previous studies, sickness was produced by rotation about a horizontal axis, and a relationship between mental task and incidence of sickness was again noted.