VISION DURING MOTION IN PATIENTS WITH ABSENT VESTIBULAR FUNCTION

We have measured a spatial visual response and visual velocity discrim ination in 3 patients with long standing vestibular loss and 6 control s. The spatial response was measured during; i) body and visual displa y stationary conditions, ii) whole-body oscillation (1Hz +/- 50 degree s/s) and iii) visual stimulus oscillation (1Hz +/- 50 degrees/s). Velo city discrimination was assessed during conditions i) and ii). The vis ual tests applied were selected on the basis that the spatial response is known to reflect peripheral processes of the retina, whereas veloc ity processing is more central in origin. Patients had normal spatial responses under static conditions and they suffered a degradation in t heir spatial responses during whole-body oscillation, whereas, normals ' responses remained unaltered. During oscillation of the visual displ ay both patients and normals suffered a degradation in their spatial r esponses, and for patients the change was very similar to that observe d during whole-body oscillation. The changes in the spatial responses were dependent on the gain of the rye movements which compensated for the whole-body or visual display oscillation. In 3 patients and all co ntrols whole-body oscillation did not alter the discrimination of velo city of a vertically moving horizontally orientated grating compared w ith when the subjects were stationary. One patient suffered a severe r eduction in the ability to discriminate velocity under whole-body osci llation, which suggests that central suppression of motion perception reduces oscillopsia.