Compensation for and adaptation to changes in the environment.

Human motor behavior is remarkably accurate, even though many everyday skills require flexible adjustments between motor activity and its consequences in extracorporeal space. The present study addressed two questions: first, how do people compensate for unpredictable changes in the environment, and second, how do they adapt to such changes? In Experiment 1, participants repeatedly and continuously drew up and down strokes on a writing pad. After drawing under a base mapping, either (a) a change of target position, or (b) a change of gain, or (c) both occurred. Compensation for gain changes occurred later than compensation for changes in target position. In addition, there were aftereffects of the previous movement in accuracy and movement time. Adaptation to changes occurred in reference to extracorporeal space, with motor constraints as a limiting factor. In Experiment 2 we obtained similar effects when participants had more time to adapt. The view that movements are planned in reference to their goals in extracorporeal space is supported.