Non-linear effects in visual suppression of vestibular nystagmus.

Visual-vestibular interaction in the control of eye movement was investigated in six subjects during exposure to a low frequency (0.05 Hz) angular oscillation about the longitudinal axis of the body at four levels of peak head velocity: 30, 60, 90 and 120 degrees/s. Eye movements were recorded whilst the subject was presented with a head-fixed visual display consisting of either a single central target or a pair of targets placed at +/- 20 degrees in the periphery. For the lower stimulus levels (30 and 60 degrees/s) the degree of suppression was reasonably constant and the vestibular nystagmus was never completely suppressed. However, during oscillation at higher velocity levels (90 and 120 degrees/s) the relationship between eye velocity and head velocity became non-linear, the degree of suppression being much less during the high velocity periods of the waveform than when the head velocity was low. The changes in suppression may be interpreted as a decrease in gain of visual feedback as a function of increasing image velocity error on the retina.