Retrieval from semantic and letter-initial categories in patients with Parkinson's disease.

We report the impaired performance by a group of 27 patients with Parkinson's disease (vs matched controls) on semantic and letter-initial verbal fluency tasks, carried out in both single and alternating category conditions. Individual differences in fluency were significantly correlated with confrontation picture naming scores in the patient group, but not in control subjects. However, the PD patients showed no significant correlation between verbal fluency scores, and rate of reciting days of the week as rapidly as possible. Both controls and patients produced more items when retrieving words from a single category than when alternately retrieving words from two categories. The magnitude of the decrement was nonetheless no greater in the patient than in the control population. This finding shows that "task switching" per se is not impaired in PD. We suggest that the verbal fluency deficit, while it may in part be attributed to motor-speech factors, primarily reflects an underlying cognitive disorder.