Figure 1

Experimental setup. A) The KINARM robot. Participants are seated in a wheel-chair base while their arms are resting on plastic arm troughs (one trough each for arm, forearm and hand). The setup permits movements of the arms in the horizontal plane, while providing full gravitational support for the participant's arms. The troughs are attached to an adjustable four-bar linkage. The experimenter adjusts the linkage and the troughs for each individual participant, insuring comfortable and correct position of the participant during the experiment. Visual targets and virtual paddles attached to the hands are displayed on a horizontally positioned monitor and two way mirror positioned below the monitor allows the subject to view the targets and paddles as appearing in the horizontal workspace of the participant's arms. The virtual environment is achieved by occluding direct vision of the participant's arms. B) A screen shot of the Object Hit task. Hand positions are displayed for illustrative purposes, but were not visible during performance of the task.