Preview control of gaze saccades: efficacy of prediction modulates eye-head interaction during human gaze saccades.

Abstract

Healthy human subjects made orienting saccades towards visual target stimuli, either with the head fixed or during intended time optimal head movements. Four experimental paradigms were used to study the influence of target predictability on eye-head coordination. They represented different sequences of horizontal target steps, that were varied in amplitude, direction and frequency. In some subjects midflight perturbations of the active head movements were applied to examine the intrasaccadic vestibulo-ocular reflex (VOR). In coordinated gaze saccades, latencies and dynamics of the eye saccade and the additional head trajectory demonstrated specific task-related changes with respect to the head fixed condition. Highly predictable target steps result in the relatively earlier onset of the head movement and an increase of the intrasaccadic head contribution to the overall gaze displacement. Differences in the level of VOR suppression became significant when gaze amplitudes exceeded 60 degrees. Consequently, an effective speed up of large gaze saccades was found with increased target predictability. We concluded, that eye-head coordination during human gaze saccades underlies high level preview control mechanisms. A parametric modulation of the intrasaccadic VOR maintains gaze accuracy, although the actual contribution of the more flexible head motor system varied, depending on gaze amplitude and prediction. The efficacy of preview control depends on interaction of these factors.