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 word-picture 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.