Ocular gaze is anchored to the target of an ongoing pointing movement

It is well known that, typically, saccadic eye movements precede goal-direc ted hand movements to a visual target stimulus. Also pointing in general is more accurate when the pointing target is gazed at. In this study, it is h ypothesized that saccades are not only preceding pointing but that gaze als o is stabilized during pointing in humans. Subjects, whose eye and pointing movements were re corded, had to make a hand movement and a saccade to a f irst target. Ar arm movement peak velocity, when the eyes are usually alrea dy fixating the first target, a new target appeared. and subjects had to ma ke a saccade toward it (dynamical trial type). In the statical trial type, a new target was offered when pointing was just completed. In a control exp eriment, a sequence of two saccades had to be made, with two different inte rstimulus intervals (ISI), comparable with the ISIs found in the first expe riment for dynamic and static trial types. In a third experiment, ocular fi xation position and pointing target were dissociated, subjects pointed at n ot fixated targets. The results showed that latencies of saccades toward th e second target were on average 155 ms longer in the dynamic trial types, c ompared with the static trial types. Saccades evoked during pointing appear ed to be delayed with approximately the remaining deceleration time of the pointing movement, resulting in "nonnal" residual saccadic reaction times ( RTs), measured from pointing movement offset to saccade movement onset. In the control experiment, the latency of the second saccade was on average on ly 79 ms larger when the two targets appeared with a short ISI compared wit h trials with long ISIs. Therefore the saccadic refractory period cannot be responsible for the substantially bigger delays that:were found in the fir st experiment. The observed saccadic delay during pointing is modulated by the distance between ocular fixation position and pointing target. The larg est delays were found when the targets coincided, the smallest delays when they were dissociated. In sum, our results provide evidence for an active s accadic inhibition process. presumably to keep steady ocular fixation at a pointing target and its surroundings. Possible neurophysiological substrate s that might underlie the reported phenomena are discussed.