The effects of Alzheimer's disease on item output in verbal fluency tasks.

We collected category fluency data from several moderate-to-large samples of participants at three different sites: the New York University Aging and Dementia Center, the Oregon Health Services Aging and Dementia Research Center, and the Einstein Aging Study at the Albert Einstein College of Medicine. These data were analyzed by calculating the average relative frequency (e.g., typicality) of the category members generated by each participant. Alzheimer's disease (AD) patients recalled fewer atypical members of common taxonomic categories than did the elderly control group. In addition, the probability of producing an item declined at a greater rate for AD patients than for the elderly control group over the duration of the task. According to sequential sampling models, this latter result implies that the rate at which AD patients search memory must be slower than the search rate of the elderly controls.