Saccade adaptation as a model of learning in voluntary movements.

Motor learning ensures the accuracy of our daily movements. However, we know relatively little about its mechanisms, particularly for voluntary movements. Saccadic eye movements serve to bring the image of a visual target precisely onto the fovea. Their accuracy is maintained not by on-line sensory feedback but by a learning mechanism, called saccade adaptation. Recent studies on saccade adaptation have provided valuable additions to our knowledge of motor learning. This review summarizes what we know about the characteristics and neural mechanisms of saccade adaptation, emphasizing recent findings and new ideas. Long-term adaptation, distinct from its short-term counterpart, seems to be present in the saccadic system. Accumulating evidence indicates the involvement of the oculomotor cerebellar vermis as a learning site. The superior colliculus is now suggested not only to generate saccade commands but also to issue driving signals for motor learning. These and other significant contributions have advanced our understanding of saccade adaptation and motor learning in general.