Impairments in the learning and performance of a new manual skill in patients with Parkinson's disease.

Twelve patients with Parkinson's disease learned two novel skills in which they had to track a target by moving a joystick. In task 1 they had to learn to anticipate the movements of a semi predictable target. In task 2 they had to learn a novel control system in which the movements of the joystick were mirror reversed in relation to the computer screen. On each task they performed two sessions of three minutes continuous practice separated by a 10 minute rest. In both tasks the patients performed much worse than the controls, but showed clear evidence of learning, particularly after the ten minute rest. Detailed examination of their performance suggested that the skill was becoming automatic, releasing attention for aspects of the task that could not be learned. The major difference from the controls appeared during the first minute of each practice session when the controls showed a marked improvement in performance while the patients did not. We suggest that this rapid but temporary improvement in performance reflects the acquisition of a motor "set" whereby existing motor programs or skills are modified to suit the task currently in hand. We concluded that patients with Parkinson's disease have difficulty in maintaining such sets.