Word fluency skills in dementia of the Alzheimer's type for common and goal-directed categories

Background : Categorisation abilities, as measured by word fluency, have been observed to deteriorate in dementia of the Alzheimer's type (DAT). Specifically, patients with early dementia have been observed to produce fewer examples than their healthy age-matched cohorts. As disease severity increases, accuracy of responses decreases. This decrease appears to be related to increased deterioration in semantic memory. Thus, exemplar generation is a sensitive indicator of early effects of dementia. Individuals' responses on word fluency have been analysed in a variety of ways and reveal unique quantitative and qualitative profiles for adults with DAT. Furthermore, type of category may also affect performance of adults with DAT. Two types of categories that have been examined are common and goal-directed categories. Aim : The purpose of the investigation was to study the categorisation skills of adults with dementia as the result of Alzheimer's disease. Specifically, the generation of goal-directed and common category exemplars by adults with mild and moderate severity DAT and normal elderly adults was examined. One concern of the study was participants' sensitivity to graded structure, examined through analysis of mean typicality ratings for responses. Another focus was identification and frequency of usage of particular response strategies. Total number of category examples produced and accuracy of these responses were also examined. Methods & Procedures : A total of 30 adults, comprising 20 individuals meeting the NINCSD-ADRDA criteria for DAT and 10 neurologically intact elderly adults, participated. Dementia severity was determined using the Global Deterioration Scale and the Dementia Rating Scale resulting in 10 mildly impaired and 10 moderately impaired DAT participants. Four common and four goal-directed categories were presented to each participant. Common categories were four of ten categories for which Rosch (1975) established typicality norms with young adults; goal-directed categories were four of sixteen for which typicality norms were developed with normal middle-aged adults (Hough, 1988). Each participant was asked to generate as many exemplars as possible for each category. No preset time limit was established for the amount of time to respond to each category. Outcomes & Results : The NBD participants produced significantly more exemplars for both category types than either DAT groups. However, the moderate DAT group was significantly less accurate than the mild DAT and NBD groups. The NBD group produced significantly more exemplars and had significantly lower mean typicality ratings for the common than the goal-directed categories; both DAT groups showed no differences between category types for these variables. Both DAT groups used fewer response strategies overall, regardless of category type, and utilised a significantly smaller percentage of semantic and subordinate association strategies than the NBD participants. Conclusions : DAT may, to some extent, adversely affect sensitivity to the general process of category construction, regardless of category type. This pervasive deficit is apparent even in milder stages of the disease process and supports the hypothesis that as severity of DAT increases, there is an accompanying increase in the deterioration of semantic memory. This greater deterioration appears to result in increased problems with creation and ordering of ideas, one of the primary bases for exemplar generation.