Post-suppression vestibulo-ocular reflex in man: visual and non-visual mechanisms

The vestibulo-ocular reflex (VOR) was intermittently suppressed by fixating a head-fixed target (light on: 9 s; darkness: 2 s) during whole-body (60–100 deg/s peak; 0.01–0.17 Hz) sinusoidal and triangular oscillation about the vertical axis for about 2 min. Eye movements associated with intervals of darkness at different phases of body oscillation were stimulus-locked averaged, thereby estimating the “post-suppression VOR”. The gain ({eye velocity}/ {head velocity}) of the post-suppression VOR was generally 26–50% of the normal gain in maintained darkness. During sinusoidal body oscillation, the phase lead of the post-suppression VOR equalled or, at low frequencies, appeared to exceed the normal lead in maintained darkness. When the light was permanently extinguished after 2 min of intermittent suppression, an initially reduced VOR rapidly (e.g., 0.4 s) appeared and required 6–30 s to build up to normal again. These observations indicated that visual suppression of the VOR dissipated in darkness with rapid and slow components. During 0.17 Hz, 60 deg/s sinusoidal oscillation, the rapid (perhaps visual) component was responsible for 1/3, and the slow (perhaps non-visual) component for 2/3, of all suppressive effects.