Clustering and switching analysis of verb fluency in individuals with Alzheimer’s disease

PURPOSE: To investigate verb fluency performance in individuals with Alzheimer’s disease compared with healthy older adults by analyzing total correct responses, number of clusters, average cluster size, and number of switches. METHODS: This is a case-control study of 39 healthy older adults and 29 older adults with a diagnosis of Alzheimer’s disease. Verb fluency performance was analyzed in terms of total number of correct verbs retrieved, number of clusters, average cluster size, and number of switches. To obtain the study outcomes, we previously conducted a procedure for categorization of the verbs that would compose the clusters. The classification of verbs was adapted for this study, including assessment by raters and analysis of inter-rater reliability. RESULTS: Individuals with Alzheimer’s disease showed significantly poorer performance than healthy controls in the number of switches and total number of correct verbs retrieved. The two groups did not differ significantly in the other measures. CONCLUSION: In this study, individuals with Alzheimer’s disease showed impaired verb fluency, characterized by a reduced number of verbs retrieved and fewer transitions between verb categories. The findings suggest that, in Alzheimer’s disease, verb fluency is more sensitive to cognitive deficits resulting from executive dysfunction than from semantic disruption.