This study compared 38 patients with Alzheimer's disease, 20 patients with
Parkinson's disease, and 51 normal controls on nonverbal, semantic, and pho
nological fluency tasks. Semantic and nonverbal fluencies declined signific
antly with age. The AD group was impaired on all fluency measures, with the
greatest impairments on nonverbal and semantic fluency. The PD group was i
mpaired on nonverbal and semantic fluencies. Differences observed in semant
ic fluency between the AD and PD groups could not be accounted for by demen
tia severity. Motor disability did not account for the PD nonverbal fluency
deficit. This study provides evidence for a semantic-based impairment in A
D and suggests that PD fluency deficits are primarily cognitive rather than
motor in nature.