Summary

The effects of vision on spatial and temporal characteristics of free unrestrained reaching movements of the arm were examined in 17 patients with ataxic syndromes due to degenerative disease of the cerebellum and its connections. Subjects were required to reach out and touch a visually presented target either in the dark or with the target and their finger visible. Overall, patients had prolonged reaction times and their movements were performed slower than normal. The spatial paths described by their fingertips were more circuitous, being of greater length than normal, a characteristic that was uninfluenced by visual conditions. Ataxic movements were less accurate than normal in two ways. First, there was greater spatial variability between repeat paths to the same target. The increased variability was present very early in the movement trajectory and at that stage was not influenced by visual feedback. Secondly, there were large constant errors at the end of movement, but only when moving in darkness. Patients with Friedreich’s ataxia as well as those with intrinsic cerebellar degeneratio