DISSOCIATIONS OF LEXICAL FUNCTION - SEMANTICS, SYNTAX, AND MORPHOLOGY

Aphasic patients who exhibit ''asyntactic comprehension'' show poor pe rformance on a sentence-picture matching task with semantically uncons trained sentences, such as ''The cow bit the horse,'' but good perform ance when the sentences are semantically constrained, such as ''The bo y threw the ball.'' The assumption has been that such patients are abl e to interpret these latter sentences by relying solely on the meaning s of the individual words, and that their intact lexical semantics can support some amount of sentence processing. We test this claim by inv estigating, in detail, the lexical semantics of an aphasic patient (JG ), whose speech production is severely agrammatic and whose sentence-p icture matching is asyntactic. We explore the semantics of JG's lexico n for both morphologically simple and complex words. We find that word meanings are represented normally in his mental lexicon, and he is ab le to use this information to integrate words into phrases. In contras t, lexical syntactic and morphological processes are severely impaired . This pattern confirms that lexical semantics can support some limite d amount of sentence processing in patients with asyntactic comprehens ion, and that different lexically based processes can be impaired diff erentially following brain damage.