Semantic dementia and pure anomia: Two varieties of progressive fluent aphasia

We compared the performance of one patient with typical semantic dementia (JL) with that of another patient (FM) who seemed to represent a different variety of progressive fluent aphasia. A series of neuropsychological and experimental investigations suggested that FM's anomia was not due to a loss of semantic knowledge or an impairment at the phonological level. These studies found the following: (1) Over time (3 years of longitudinal testing) FM had only a mild and stable impairment on tests of semantic memory, unlike other patients with semantic dementia, who often show rapid decline on such tests. (2) While FM performed at ceiling on tests of immediate single word repetition, she often lost the phonological form of words when a delay was introduced between her hearing the word and attempting to produce it. By contrast, her ability to perform word-picture matching tests was not affected by a timed delay, suggesting that she still had access to semantic information about the spoken word. (3) By using two gating experiments in which FM heard and had to identify incrementing fragments of concrete words, she showed near normal performance and minimal benefit from the provision of a semantic clue in the form of a picture of the spoken word. These results suggest that FM's deficits were due to a loss of communication between semantic memory and the phonological output lexicon: a case of progressive pure anomia rather than semantic dementia