MONKEY SACCADIC LATENCY AND PURSUIT VELOCITY SHOW A PREFERENCE FOR UPWARD DIRECTIONS OF TARGET MOTION

SACCADIC latency was studied as a function of the direction of sudden target displacements (steps) and of subsequent smooth target motion (r amps) in Macaca fascicularis. The monkey fixated a central spot that s uddenly changed its position and then moved constantly at 10 deg s(-1) , thus eliciting initial saccades and subsequent pursuit eye movements (recorded by a magnetic search-coil technique). Latencies for initial saccades differed markedly in the vertical axis, being shorter in upw ard than downward directions for both step and ramp components of targ et motion. Saccadic latency was also related to the mean pursuit veloc ity, indicating that the oculomotor system accounts for the direction of step and ramp components of target motion in an integrative way.