Selective impairment of semantics in lexical processing

Abstract

We report the performance of a neurologically impaired patient, KE, whose frequent errors in reading, writing, naming, and comprehension were nearly always semantically related to the target response. To quantify this pattern, a large number of items were presented for tasks of verbal and written naming, oral reading, writing to dictation, word/picture matching, and naming from tactile exploration. Detailed analyses of his performance on these tasks show very similar rates and types of errors, regardless of the modality of stimulus or response. KE's homogeneous pattern of semantic errors across modalities is interpreted as evidence for selective damage to a semantic system common to all lexical processes. In addition, although KE demonstrated some spared knowledge of all items in response to picture stimuli, we were able to interpret all aspects of his performance without resorting to a proposal that there are modality-specific semantic systems. Finally, we show that our interpretation, which assumes a unitary, modality-independent semantic system, can also account for previously reported cases in the cognitive neuropsychology literature that have been taken as evidence for modality-specific semantic systems.