CLUSTERING AND SWITCHING ON VERBAL FLUENCY TESTS IN ALZHEIMERS AND PARKINSONS-DISEASE

Two components of verbal fluency performance-clustering (i.e., generat ing words within subcategories) and switching (i.e., shifting between subcategories)-were examined in patients with dementia of the Alzheime r type (DAT), patients with dementia with Parkinson's disease (DPD), n ondemented patients with Parkinson's disease (NPD), and demographicall y matched controls. The DAT and DPD groups were impaired in the number of words generated on both phonemic and semantic fluency. The DAT gro up produced smaller clusters on both tasks and switched less often on semantic fluency than controls. The DPD group switched less often on b oth tasks and produced smaller clusters on phonemic fluency than contr ols. The NPD group was not impaired on any fluency variable. Thus, the total number of words generated on phonemic and semantic fluency did not discriminate the dementia groups from their respective control gro ups, but measures of clustering and switching did. This differential p attern of performance provides evidence for the potential usefulness o f measures of switching and clustering in the assessment of dementia.