Naming and category concept generation in older adults with and without dementia

Abstract

Background: An intact semantic memory system is vital for accurate naming of objects; naming failures exhibited by individuals with dementia have been a means of identifying the nature of the semantic memory impairment. However, naming impairment has also been reported in healthy older adults. Categorisation is a process of concept formation within semantic memory. Category type influences ability to synthesise category concepts. Studies investigating categorisation skills in adults with dementia have revealed deterioration in conceptual knowledge as compared to age-matched healthy cohorts. Aims: It is hypothesised that normal older adults are impaired at the lexical access stage of word retrieval; those with dementia have deficits in the earlier concept identification stages of word retrieval and lexical access difficulties. Methods & Procedures:A group of adults with dementia of the Alzheimer's type (DAT) and a group of normal elderly adults were examined on naming and category concept generation tasks relative to accuracy and error types. Participants were 15 adults with DAT and 15 age-, education-, and gender-matched neurologically intact adults. MMSE results supported division of two groups. All participants were native English speakers, literate, with normal hearing. Experimental tasks were the Test of Adolescent/Adult Word Finding (TAWF) and a category concept generation task (CCGT). For the CCGT, participants were presented with four category examples for common and goal-directed categories and instructed to provide a category label. Context vignettes accompanied category examples for half the categories. Outcomes & Results: For the TAWF, there were no significant group differences for standard scores. Further analysis revealed that: (1) the control group performed significantly poorer on picture naming: nouns than any other subtest; (2) normal controls performed better than the DAT group on all subtests except picture naming: nouns; and (3) the DAT group performed significantly worse on category naming than all other subtests. Analysis of CCGT revealed that: (1) normal controls performed better than the DAT participants on goal-directed categories with context but not without context; (2) performance was higher for goal-directed categories with context for controls only; and (3) performance was higher on common than goal-directed categories without context for controls. Conclusions:The results indicate that normal older adults are impaired in lexical access; those with DAT have deficits in the earlier conceptual stages of word retrieval in addition to lexical access difficulties. DAT participants especially had difficulty with category naming. The DAT adults showed minimal differences in performance from a no-context to context condition. The findings support previous research that adults with DAT display semantic memory impairments.