Abstract

The role of the vestibuloocular reflex (VOR) on the control of body posture in normal subjects was examined, using a sinusoidal chair. Eye responses during four different rotation frequencies and velocities of the whole body (at the frequency of 0.1 Hz and the velocity of 48-50 o/s, 0.2 Hz and 75-88 o/s, 0.5 Hz and 148-179 o/s, and 1.0 Hz and 105-47 o/s) were examined in three VOR conditions: normal VOR, suppressed VOR, and enhanced VOR. The following results were obtained: (1) The rotatory stimulus evoked two types of eye movement: nystagmus and a gross eye movement. Nystagmus was composed of a fast component and a slow component; (2) The fast component of nystagmus was in the same direction to a rotatory stimulus, and the slow component was in the opposite direction. The direction of the gross eye movement was always in the opposite direction to that of the stimulus; (3) In the normal VOR condition, the frequency of nystagmus decreased as the frequency of the stimulus increased, and the velocity of nystagmus increased as the velocity of the stimulus increased; (4) In the suppressed VOR condition, the suppression ratios (normal VOR/ suppressed VOR) of the frequency and of the velocity of nystagmus decreased as the frequency of the stimulus increased; (5) In the enhanced VOR condition, the eye movement responses were similar to those of the normal VOR condition, but many subjects complained about subjective symptoms of motion sickness. Thes results show that the VOR plays an important role in the control of body posture. Verf.-Ref.