ABSTRACT
The demands for the two oculomotor subsystems, smooth pursuit and the vestibulo-ocular reflex (VOR), differ considerably. The pursuit system is designed to keep small, moving targets on the fovea by smooth eye movements. The restriction of three-dimensional (3D) eye position to a common plane might facilitate the coordination between smooth pursuit, saccades and fixation. The vestibular system detects the angular motion of the head in 3D space and the brain uses these signals to program 3D eye movements aimed at stabilizing the retinal image. VOR slow phase eye velocities depend systematically on current eye position. Static changes of the head relative to gravity induce changes in 3D eye position during and in between saccades. The effect of these tonic otolith inputs on 3D eye position has been examined by determining Listing’s plane during various static positions. Closer inspection of the postrotatory eye velocity revealed quantitative differences for the different VOR planes.
