Coupling of eye, finger, elbow, and shoulder movements during manual aiming

Temporal and spatial coupling of point of gaze (PG) and movements of the fi nger, elbow, and shoulder during a speeded aiming task were examined. Ten p articipants completed 40-cm aiming movements with the right arm, in a situa tion that allowed free movement of the eyes, head, arm, and trunk. On the m ajority of trials, a large initial saccade undershot the target slightly, a nd 1 or more smaller corrective saccades brought the eyes to the target pos ition. The finger elbow, and shoulder exhibited a similar pattern of unders hooting their final positions, followed by small corrective movements. Eye movements usually preceded limb movements, and the eyes always arrived at t he target well in advance of the finger. There was a clear temporal couplin g between primary saccade completion and peak acceleration of the finger, e lbow, and shoulder. The initiation of limb-segment movement usually occurre d in a proximal-to-distal pattern. Increased variability in elbow and shoul der position as the movement progressed may have served to reduce variabili ty in finger position. The spatial-temporal coupling of PG with the 3 limb segments was optimal for the pick up of visual information about the positi on of the finger and the target late in the movement.