Evidence for a context-sensitive word retrieval disorder in a case of nonfluent aphasia.

We describe a patient (BM) with nonfluent aphasia who presents with sparse, fragmented spontaneous speech but normal or near-normal performance on standard naming tasks. However, more detailed investigation revealed some unusual features to BM's naming: On a task involving repeated naming of a small set of targets, his performance degenerated when the targets were semantically blocked, particularly at fast rates of presentation. This semantic blocking effect was not observed in an analogous wordpicture matching task. Also, it was not present on a task where a set of words had to be named repeatedly in a fixed, predictable sequence. Finally, a fluent aphasic patient who presented with a classic "output" anomia failed to show the semantic blocking and predictability effects. It is suggested that BM suffers from a context-sensitive word retrieval disorder. The disorder is attributed to a difficulty in modulating activation within the lexical network. Implications for nonfluent aphasia, as well as for models of lexical retrieval, are discussed.