Abstract
Visual feedback has been shown to play a pivotal role shaping metrical and efficient spatiotemporal grasping parameters (Jeannerod, 1985). In the present investigation, we sought to determine the degree visual feedback predominates the exemplar specification of grasp kinematics (i.e., peak grip aperture, time to peak grip aperture) by applying an intrinsic afferent perturbation to the grasping limb. Specifically, participants completed closed-loop (i.e., with continuous visual feedback) and open-loop (i.e., visual feedback withdrawn at movement initiation) grasps to midline objects in the depth plane under an environment wherein 33% of the trials entailed an unexpected and small amplitude (1 mm) high-frequency (70 Hz) vibration to the antagonist muscle (i.e., the biceps) of the grasping limb. The purpose of the tendon vibration was to induce erroneous sensory feedback concerning the reaching characteristics (e.g., absolute position and velocity) of the grasping limb. For closed- and open-loop trials performed without tendon vibration, maximal grip aperture scaled with veridical object size and occurred at approximately 70% of movement time. Interestingly, closed-loop trials performed with tendon vibration elicited kinematic parameters parallel to non-vibrated counterparts whereas open-loop trials showed a decrease in grip aperture scaling and delayed onset of maximal grip aperture. Moreover, time-course examination of grasp kinematics showed that closed-loop grasps were refractory to tendon vibration throughout the movement trajectory; however, open-loop grasp parameters were sensitive to an early (i.e., at peak acceleration) and continuous influence of tendon vibration. Those results confirm the central role of vision in the specification and online control of action and provide putative evidence of an inhibitory central nervous system mechanism, or mechanisms, allowing vision to supercede other afferent resources for the online control of reach and grasp movements.