EYE TORSION ELICITED BY OSCILLATING GRATINGS - EFFECTS OF ORIENTATION, WAVELENGTH AND STATIONARY CONTOURS

We studied binocular cyclorotatory (torsional) eye movements in respon se to gratings that oscillated sinusoidally in a frontal plane. The sq uare-wave gratings viewed by the right and left eye were presented and controlled separately to induce cycloversion and cyclovergence by osc illation in phase and out of phase. Eye movements were recorded with s cleral induction coils. Stimulus oscillation frequency ranged from 0.1 25 to 1 Hz and the wavelength of the gratings ranged from 0.92 to 25.7 5 deg of visual angle. Cycloversion and cyclovergence gain were, on av erage, comparable in magnitude and decreased with increasing oscillati on frequency. There was no consistent effect of the wavelength on the magnitude of the responses. In general, responses were considerably hi gher to gratings that were oriented horizontally than to those oriente d vertically. This anisotropy was present both in cycloversion and cyc lovergence. It was enhanced in a larger sized stimulus and by presenti ng stationary, orthogonal contours (mimicking a ''shear'' movement), b ut it was not consistently influenced by wavelength. Cyclovergence sho wed a phase lag, which increased with oscillation frequency but which was independent of wavelength. In contrast, cycloversion showed a slig ht phase lead which was independent of both oscillation frequency and wavelength.