The neurocognitive basis of word-finding difficulty in Alzheimer's disease

Past research has indicated that deficits in the areas of visual perception, semantic memory, and word availability may each underlie the word-finding difficulty observed in dementia of the Alzheimer type. This study attempted to evaluate the independent contribution of deficits in each of these cognitive domains to naming ability in a single sample of patients. In comparison to a group of age- and sex-matched normal controls, performance by the mid to moderate Alzheimer patients indicated deficits in all three functional areas. Using multiple linear regression, with dementia severity, knowledge of word meaning, and visuoperceptual processing as predictors, 59.6% of naming variance was accounted for. However, after controlling for the nonspecific effects of dementia on naming, knowledge of word meaning remained as the only specific deficit which continued to predict naming accuracy. Measures of visual perception and word availability were independent of naming ability. The results were interpreted as indicating that in the mild to moderate stages of disease progression, dysnomia is a sensitive index of the generalised effects of dementia with a specific component due to impairment in semantic memory, which is independent of visuo-perceptual and word-availability processes.