Vision during motion in patients with absent vestibular function.

We have measured a spatial visual response and visual velocity discrimination in 4 patients with long standing vestibular loss and 6 controls. The spatial response was measured during; i) body and visual display stationary conditions, ii) whole-body oscillation (1 Hz +/- 50 degrees/s) and iii) visual stimulus oscillation (1 Hz +/- 50 degrees/s). Velocity discrimination was assessed during conditions i) and ii). The visual tests applied were selected on the basis that the spatial response is known to reflect peripheral processes of the retina, whereas velocity processing is more central in origin. Patients had normal spatial responses under static conditions and they suffered a degradation in their spatial responses during whole-body oscillation, whereas, normals' responses remained unaltered. During oscillation of the visual display both patients and normals suffered a degradation in their spatial responses, and for patients the change was very similar to that observed during whole-body oscillation. The changes in the spatial responses were dependent on the gain of the eye movements which compensated for the whole-body or visual display oscillation. In 3 patients and all controls whole-body oscillation did not alter the discrimination of velocity of a vertically moving horizontally orientated grating compared with when the subjects were stationary. One patient suffered a severe reduction in the ability to discriminate velocity under whole-body oscillation, which suggests that central suppression of motion perception reduces oscillopsia.