We investigated the effect of morphosyntactic violation type on accuracy and processing time in Broca's aphasics engaged in an on-line error detection task. Five agrammatic Broca's aphasic subjects and 15 age-matched control subjects performed grammaticality judgments on auditorily presented grammatical and ungrammatical sentences. Both judgment accuracy and decision time were measured, so that the data revealed not only whether aphasics detected violations, but when they noticed them. The ungrammatical sentences were created by changing quantifiers and auxiliary verbs in one of two ways: substituting one quantifier or auxiliary for another to create agreement errors, or moving the quantifier or auxiliary “downstream” from its proper site to create word order errors. Also, the position of the violation in the sentence (early versus late) as well as the distance relationships among sentence elements involved in the violation (local versus global) were manipulated.

Results suggest that aphasic subjects retain some sensitivity to grammaticality, knowledge that they are able to use “online.” Performance was also affected by type of violation. Aphasic subjects were less sensitive to agreement violations than they were to violations created by moving the same elements to an illegal position—and this tended to be reflected in decision times as well as accuracy.

These results support two conclusions. First, although the performance of aphasic subjects was degraded relative to control subjects, the findings of overall grammaticality sensitivity and relatively rapid decision times suggest that the locus of grammatical impairment in these patients has more to do with the accessing of linguistic information than with loss of linguistic knowledge. Second, the difference between agreement and movement violations provides further evidence that morphological marking is relatively vulnerable in aphasia, compared with the principles that govern word and morpheme ordering.

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