Clustering strategies on tasks of verbal fluency in Parkinson's disease.

The verbal output of patients with Parkinson's disease (PD) was analyzed for semantic and phonemic clusters on tasks of verbal fluency. One task required cued retrieval by semantic category (i.e. animals), and one required non-cued retrieval by initial letter (e.g. words beginning with 'F'). Nondemented PD patients (N = 25) produced significantly fewer words on the cued semantic retrieval task than age-, gender- and education-matched normal control subjects (N = 22), but were not impaired on the non-cued letter retrieval task. However, overall, PD patients were able to form more semantic clusters than phonemic clusters. These results are discussed in light of other studies of verbal fluency deficits in patients with PD.