Aphasic sentence comprehension as a resource deficit: a computational approach.

This article describes a new computational model of aphasic sentence comprehension. The model is based on the premise that all aphasics, however different, share a common deficit which determines a considerable amount of the individual variation observed in their sentence comprehension performance. This common deficit is construed as a pathological reduction in the activation resources of a working memory system that subserves sentence comprehension (Miyake, Carpenter, & Just, 1994). To test the theoretical feasibility of the resource reduction hypothesis, a new computer model of aphasic sentence comprehension was developed and tested. We describe the model as well as some initial simulation results, indicating that the model can account for some of the sentence complexity and severity effects that have been reported in the aphasia literature.

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.

The production of grammatical morphology in Broca's and Wernicke's aphasics: speed and accuracy factors.

A group of Broca's aphasics (BA), Wernicke's aphasics (WA) and normal controls participated in a CLOZE experiment which required the oral production of various types of free and bound morphemes. Results provided support for the hypothesis that BA and WA share the same underlying impairment in the production of grammatical morphology. The relative difficulty of the various free and bound morpheme types was the same for BA and WA. This appeared to be the case not only in an analysis of the number of errors but also in an analysis of response times. The same analyses furthermore revealed no significant differences in the absolute levels of performance of BA and WA. Finally, it was found that BA and WA show the same relative contribution of within- and across-category substitutions of free morphemes. For bound morphemes, there was a slight difference between BA and WA, in that BA exclusively produced within-category substitutions while WA also produced some across-category substitutions.