Picture naming and progression of Alzheimer's disease: an analysis of error types.

Seven patients affected by Dementia of the Alzheimer Type (DAT) took part in a longitudinal study aimed at assessing the qualitative and quantitative evolution of picture naming impairment. The follow-up lasted 6-36 months and the patients were examined at intervals of 6 months or longer. We found that the absolute number of lexical-semantic errors tended to be constant or to rise slightly until an advanced stage of DAT severity was reached. However, the proportion of errors of the lexical-semantic type in relation to the overall number of errors showed a decline as the disease progressed, with empty and unrelated responses being increasingly observed. Visual errors were generally a minority; they were produced in different proportions for each patient but did not vary greatly over time. For the observed patients, the proportion of lexical and semantic errors was inversely related to the overall naming performance, following a negative logarithmic function. This finding was replicated analysing cross-sectional data from another 24 DAT patients who were given the same naming task.