Pursuit and saccadic eye movements in response to unpredictable constant velocity targets

Pursuit eye movements in response to unpredictable reversals of constant velocity target motion at 20 degrees, 40 degrees and 60 degrees/s were analysed in 20 normal subjects. The gain in smooth pursuit was originally determined by the preceding target duration; the shorter the preceding movement, the longer was the acceleration of pursuit velocity inhibited. The ongoing target duration secondarily affected the gain at faster target velocities by restricting time for eye velocity acceleration. Whereas the saccadic reaction time was around 200 ms, the intersaccadic interval shortened as target velocity increased. The saccadic amplitude increased in direct proportion to an increase in target velocity. The present study showed that, even under irregular stimulations, pursuit eye movement is regulated in a feedforward manner by the perceptual analysis of the preceding target motion, and that corrective saccades in pursuit eye movement correspond to those observed in step displacements, except for the programming on the basis of the changing rate of position error.