Procedural learning eliminates specific slowing down of response selection in patients with idiopathic Parkinson syndrome.

Patients with idiopathic Parkinson syndrome and normally aged controls participated in a psychological refractory period experiment. Two tasks were presented on each trial: auditory discrimination of high versus low tones, followed by visual classification of letters versus their mirror images. Speeded responses to both tasks were required. Stimulus onset asynchrony between the tasks was varied (short vs. long). Both groups showed equal response times overall, but patients were slower on the second task in the short stimulus onset asynchrony condition. This effect was eliminated with practice. The results were interpreted in terms of reduced capacity for cognitive processes involving decision making as a secondary symptom of the Parkinson syndrome.