Torsional eye movements are facilitated during perception of self-motion

Visual motion in the roll plane elicits torsional optokinetic nystagmus (tO KN) with intermittent periods of illusory, contradirectional self-motion (c ircularvection, CV). The CV may also have a component of whole-body tilt if the axis of stimulus rotation is not aligned with the direction of gravity . We report how the characteristics of tOKN are affected by the presence of CV. Subjects had their eye movements recorded by VOG whilst viewing a full -field stimulus rotating at 30-60 degrees/s about their naso-occipital axis . They were tested in upright and supine posture and signalled the presence -absence of CV with a pushbutton. In both postures, during CV, tOKN slow-ph ase gain was found to be enhanced and average torsional eye position shifte d in the direction opposite to stimulus rotation. When supine, slow-phase g ain was greater than when upright both during the perception of object-moti on and during CV. The effects may be explained in terms of a relegation of restraining vestibular input to the torsional oculomotor system during CV a nd illusory tilt.