Sentence processing in fluent and non-fluent aphasia

The most notable feature of Broca\u27s aphasia is agrammatic speech production, with loss of fluency and constriction of vocabulary. In addition, some Broca\u27s aphasics have been found to exhibit difficulties in sentence comprehension, though the source of their comprehension problems remains controversial. One theory of agrammatism identifies impairment of the syntactic component, predicting errors both in comprehension and production. If there is a central syntactic deficit, then Broca\u27s aphasics patients would be expected to perform poorly on sentences in which the correct interpretation hinges on a full syntactic analysis, independent of variations in other task demands. They would also be expected to yield a different pattern of errors than Wernicke\u27s aphasics on sentences with complex syntactic structure.^ To investigate these predictions the present study tested Serbo-Croatian speaking aphasics (seven Broca-type aphasics with agrammatic output; five Wernicke-type aphasics). The test sentences were semantically reversible relative clauses, which were administered in three different experimental tasks; grammaticality judgments, sentence-picture matching, and judgments of semantic anomaly. Because it minimizes nonsyntactic processing demands, the grammaticality judgment task was expected to provide the most accurate measure of syntactic competence. The sentence-picture matching task was used to provide a basis for cross-task comparison and for comparison with results of previous studies. Judgments on the semantic anomaly task also served for cross-task comparison and as a control for subjects\u27 semantic comprehension of the sentences.^ The results showed that non-fluent aphasics can process complex syntactic structures, as evidenced by their performance with relative clauses on the grammaticality judgment task. Their rate of successful performance was considerably lower on the other tasks, however. The pattern of errors by Broca-type aphasics closely resembled the pattern displayed by Wernicke-type aphasics and normal subjects. These findings are interpreted as support for the view that comprehension deficits in agrammatism reflect varying degrees of loss of processing ability, but sparing of syntactic knowledge. Although use of grammatical knowledge is impaired in some tasks, it can be exploited successfully in tasks that minimize processing load.