The visual consequences of deviations in the orientation of the axis of rotation of the human vestibulo-ocular reflex

The 3D orientation and amplitude of the movement of each eye evoked by predictable, sinusoidal and non-predictable, sum-of-sines rotation about roll, yaw, pitch and intermediate axes were measured in seven subjects. The rotation axis of the eyes was not always perfectly aligned with the stimulus axis but showed systematic deviations that depended on the orientation of the rotation axis of the head. Misalignment of the oculomotor response with the stimulus axis is equivalent to adding an orthogonal, non-compensatory vector that potentially could introduce retinal slip, rather than compensate for it. The variations in orientation could not be readily explained as an artifact arising from the differential processing of the roll component. Instead, differences in the movements of the left and right eyes had trends appropriate for compensating for the geometrical demands of the translation of the eyes that must necessarily accompany natural head rotation.