On-line sensitivity to subject-verb agreement violations in Broca's aphasics: the role of syntactic complexity and time.

This study examined on-line sensitivity to subject-verb agreement violations in patients with Broca's aphasia and age-matched controls using a word monitoring paradigm. The agreement violations were couched in either simple or complex syntactic frames. In a first experiment, these syntactic frames were immediately followed by the noun phrase containing the target, whereas in the second experiment a 750-msec separation was introduced. The main finding of the first experiment was that patients with Broca's aphasia showed an agreement effect only for simple (i.e., conjoined) sentences but not for complex (i.e., embedded) ones, while controls showed the expected agreement effect for both. The results of the second experiment demonstrated further that the 750-msec delay in target presentation abolished the agreement effect in Broca's aphasics but not in normal controls. The findings are interpreted to suggest that Broca's suffer from a pathological limitation in parsing capacity, giving rise to a faster than normal decay of syntactic information.