Active error corrections enhance adaptation to a visuo-motor rotation.

In two experiments we studied the role of active movements for adaptation to a visuo-motor rotation by way of adding external forces. In the first experiment we compared practice with target guidance and path guidance with a no-guidance control condition. With target guidance the arm was driven to the target on a straight path, whereas with path guidance active movements were required which were driven to the correct straight path of the hand whenever there was a deviation. During practice target guidance resulted in faster movements with smaller initial direction errors than in the other two conditions. However, in subsequent visual open-loop tests the adaptive shifts turned out to be smaller after both target-guidance and path-guidance practice than after no-guidance practice. In the second experiment resistive path guidance during practice was compared with a no-guidance control condition. With resistive path guidance the hand was driven away from the correct straight path whenever there was a deviation. Thus, corrections required active movements and could not be passive as with assistive path guidance in the first experiment. During practice resistive path guidance resulted in longer movement time than in the no-guidance group. Adaptive shifts, as assessed in subsequent open-loop tests, were not different between the two groups. According to these findings adaptation to a visuo-motor rotation is driven by active error corrections.