Adaptive changes in automatic motor responses based on acquired visuomotor correspondence.

The present study tested whether remapping of visuomotor correspondence alters automatic motor responses induced by visual stimuli. We hypothesized that the congruency effect, an automatic modulation of motor responses based on stimulus-response congruency, changes in accordance with a new visuomotor correspondence acquired through an adaptation task. To induce visuomotor adaptation, participants performed a tracking task with 30° or 150° rotation of the visual feedback. The congruency effect was evaluated multiple times by a visual response task where participants moved their finger left or right. We predicted that the congruency effect, as a measure of automatic responses, would be almost reversed after adaptation to the 150° rotation, because a visual stimulus spatially opposite to the participant's own action would become a "congruent" stimulus in a 150°-rotated environment but not in a 30°-rotation environment. The results show that visuomotor adaptation to the 150° rotation did modulate the congruency effect in accordance with the acquired visuomotor correspondence, but did not completely reverse the effect. When the effect was assessed after the manipulation, which was assumed to switch an internal model back to its normal state, there was no change in automatic motor responses. Furthermore, we found that after effects developed as the training proceeded but decreased over time. These findings suggest that the visuomotor system subserving automatic modulation in motor responses is based on the currently active internal model and, therefore, highly adaptive. In addition, the mechanism underlying after effects in a visuomotor task is discussed in terms of a switching function of internal models.