Target velocity based prediction in saccadic vector programming

Two experiments have been designed to test whether the saccadic system takes target motion into consideration in computing saccade amplitude. In one experiment, while the subject fixated straight ahead, either a horizontal ramp-step-ramp or a horizontal step-ramp target moved from left to right. After the step, the subject had to make a saccade and follow the target. In the second set of experiments, the target, after an initial step, moved extrafoveally from up to down at fixed velocity; a tone, signaling the subject to make a saccade to the target and follow it, was delivered either after a variable delay (previewed condition) or simultaneously with the initial target step (non-previewed condition). In both experiments, eye position at saccade end was statistically different from target position 100 msec before saccade onset only when the target slow motion was presented before the step (i.e. in horizontal ramp-step-ramp and in previewed H-step V-ramp paradigms), suggesting that target motion could be used by the saccadic system to extrapolate the future target position, only if the subject is given enough time to observe the target ramp motion before the step.