The experimental paradigm used in this study. Subjects performed self-paced bimanual movements, either symmetric (Symmetric task) or asymmetric (Asymmetric task), of both thumbs. The other task was that both hands were kept stationary (Stationary task). The three tasks were conducted with normal visual feedback (NoMirror condition) and non-veridical visual feedback (Mirror condition). In the Asymmetric task of the Mirror condition, since the actual visual information on left hand movement was masked by the mirror, subjects saw symmetric movements despite performing asymmetric movements. By contrast, in the Symmetric task, although subjects saw the mirrored movement, the phase of bimanual movement was the same for masked and mirrored hands. Electrical stimulation for the recording of somatosensory responses was delivered to the median nerve at the left wrist.