Coordinated Eye-Head Movements in the Cat

Abstract

Coordinated movements of the eyes and head were first studied systematically in the monkey by Bizzi et al. 1971; Morasso et al. 1973; and Dichgans et al. 1973. In these classic studies they showed that an animal, orienting to a randomly appearing visual target, encodes the same saccadic eye movement signal in both the head fixed and head free conditions. In the head free condition the vestibularly induced compensatory eye movement produced by the head movement is added linearly to the saccade signal. Since the compensatory eye movement is in the opposite direction to the saccade, saccade velocity and amplitude for a given target eccentricity are reduced. The elegance of this system is that an eye movement can be programmed independently of the head movement, and that a high degree of accuracy is achieved because the vestibulo-ocular reflex (VOR) enables the gaze to reach and stay on-target irrespective of what the head does. This strategy will be called the saccade attenuation (SA) strategy.