The nature of the naming deficit in Alzheimer's and Huntington's disease.

A comparison of naming performance, on the Boston Naming Test, of 52 patients with dementia of Alzheimer's type (DAT), 16 patients with Huntington's disease (HD) and 52 normal control subjects was performed using a comprehensive classification of error types. Spontaneous and cued naming scores were significantly impaired both in the DAT and HD groups, but performance in the DAT patients was significantly worse than that of the HD patients. Normal controls made predominantly semantic-category and circumlocutory errors. The HD group differed from normal only in the proportion of visually based errors, which was greater in the patient group. By contrast, the DAT patients made a significantly greater proportion of semantic-superordinate and semantic-associative errors. The same pattern of naming errors was found when a group of DAT and HD patients matched for overall naming ability was compared. A subgroup of 22 DAT patients was followed longitudinally over 3 y. Their deterioration in overall naming performance was accompanied by a consistent change in the profile of naming errors: the proportion of semantic-associative errors increased significantly as did the proportion of visual errors. These results are considered in the light of current cognitive models of naming. They suggest that in HD, naming deficits initially involve disruption of perceptual analysis, whereas in DAT such impairments in the early stages reflect a breakdown in semantic processes. However, as DAT progresses, perceptual problems also begin to contribute to the patients' naming difficulties. Postlexical (phonemic) processes remain relatively intact throughout in both diseases.