Visual feedback of the hand and target guides goal-directed reaching movements. However, the magnitude of visuomotor responses to visual shifts of hand location are not consistent throughout the movement, but evolve temporally, peaking in the middle and falling as the hand nears the target (1,2). We previously showed that the two visual feedback systems of hand and target motion elicit partially independent responses that are integrated in later stages of the sensorimotor system (3), arguing against the difference vector model of visually guided reaching. This result also suggests that the evolution of feedback might differ in these two systems. Here we examined to what degree the temporal evolution of the visuomotor feedback gain of the target differs from the visuomotor feedback gain of the hand. Participants performed reaching movements to a target while grasping a robotic manipulandum. Visual feedback of both the hand position (cursor) and target position was provided in the plane of movement using a virtual reality setup. On random probe trials the cursor or target was momentarily laterally displaced visually before returning to the actual hand or target position. On all probe trials the hand trajectory was constrained by a mechanical channel in order to measure the resulting feedback force. The perturbations occurred at thirteen different times prior to movement initiation, during movement, or after movement completion. The involuntary force responses to both target and cursor shifts exhibited a strong temporal evolution, and were not present before or after the movement.Consistent differences in the temporal pattern of hand and target responses further demonstrate independent control of visual feedback systems for hand and target motion.     «

Visual feedback of the hand and target guides goal-directed reaching movements. However, the magnitude of visuomotor responses to visual shifts of hand location are not consistent throughout the movement, but evolve temporally, peaking in the middle and falling as the hand nears the target (1,2). We previously showed that the two visual feedback systems of hand and target motion elicit partially independent responses that are integrated in later stages of the sensorimotor system (3), arguing ag...     »