Contribution of perceptual and lexical-semantic errors to the naming impairments in Alzheimer's disease.

The contribution of perceptual and semantic processing deficits to naming-test performance by Alzheimer's Disease subjects was examined. Groups of 34 Alzheimer subjects and 25 elderly controls completed tests of naming standard line drawings and naming perceptually degraded figures, and a test of verbal fluency for a specific semantic category. Alzheimer subjects were impaired on all measures and, when their naming-test errors were analyzed, they showed higher proportions of perceptual errors and failures to respond. Further, considerable variability in the proportions of different types of error was found both among subjects and among test items. These findings indicate that poor naming-test performance cannot necessarily be attributed to a specific deficit in semantic processing. Also, the discrepancies between previous reports of the naming deficits in Alzheimer's Disease may reflect differences in task difficulty and item selection that were apparent in this study.