Eye-hand coordination in object manipulation

We analyzed the coordination between gaze behavior, fingertip movements, an d movements of the manipulated object when subjects reached for and grasped a bar and moved it to press a target-switch. Subjects almost exclusively f ixated certain landmarks critical for the control of the task. Landmarks at which contact events took place were obligatory gaze targets. These includ ed the grasp site on the bar, the target, and the support surface where the bar was returned after target contact. Any obstacle in the direct movement path and the tip of the bar were optional landmarks. Subjects never fixate d the hand or the moving bar. Gaze and hand/bar movements were linked conce rning landmarks, with gaze leading. The instant that gaze exited a given la ndmark coincided with a kinematic event at that landmark in a manner sugges ting that subjects monitored critical kinematic events for phasic verificat ion of task progress and subgoal completion. For both the obstacle and targ et, subjects directed saccades and fixations to sites that were offset from the physical extension of the objects. Fixations related to an obstacle ap peared to specify a location around which the extending tip of the bar shou ld travel. We conclude that gaze supports hand movement planning by marking key positions to which the fingertips or grasped object are subsequently d irected. The salience of gaze targets arises from the functional sensorimot or requirements of the task. We further suggest that gaze control contribut es to the development and maintenance of sensorimotor correlation matrices that support predictive motor control in manipulation.