Effects of thematic structure on syntactic comprehension in aphasia

This study assessed aphasic subjects' sensitivity to the given-new structure within simple paragraphs and the extent to which narrative discourse is facilitative of syntactic processing in the absence of semantic constraints. Subjects were divided into four groups along the dimensions of comprehension level and fluency. Stimulus items consisted of reversible active and passive sentences that were presented in the following three conditions: isolation, at the end of paragraphs such that the given-new structure was respected, and at the end of paragraphs such that the given-new structure was violated. Fluency did not significantly influence performance but comprehension level did. The high-comprehension group presented no significant differences between contextual conditions. The low-comprehension group, however, favored both paragraph contexts over isolation with no difference occurring between contextual conditions. These results suggest that lower level aphasic subjects are able to utilize thematic, antecedent verbal information for comprehending sentences in connected discourse even when the discourse is not semantically predictive of the underlying meaning of these sentences. Whether the narrative respects or violates the given-new relationship may not be an important factor. The reasons for these findings are explored.