Language disorders secondary to focal brain damage can cause a variety of disruptions to the ability of aphasic speakers to understand and produce sentences. This project investigates the functional bases of sentence processing disorders from the perspective of what is known about normal language processing. Primary focus is on the role of the verb in sentence comprehension and production, on the assumption that impairments that selectively affect verb representation or processing in aphasia will have important effects on sentence processing. Emerging functional neuroimaging methods, which can identify distinct patterns of neural activation associated with different language tasks, are also used to test hypotheses about the independence and interrelationships among language processing components. In the next project period, five experiments will investigate the important question of whether noun/verb distinctions found among aphasic speakers and in previous neuroimaging studies reflect semantic or syntactic differences between words. A related issue to be studied in the same experiments is the extent to which grammatical class ambiguity affects word processing. Two experiments will investigate effects of syntactic and semantic factors in aphasic sentence comprehension. The word-monitoring paradigm will be used to determine the sensitivity of patients to 1) the different syntactic consequences of some semantically related verbs, and 2) to the semantic relationships between verbs and the nouns that are potential fillers of their thematic roles. Two additional experiments based on the same set of theoretical issues that underlie the monitoring experiments will be conducted to elicit sentences with specific structures. Two experiments using functional Magnetic Resonance Imaging (fMRI) with normal subjects during sentence processing will seek to distinguish brain activation patterns that may be attributable to syntactic or semantic processes. These studies differ from much previous work on this issue in that they employ relatively simple sentences or phrases, and they focus subjects? attention on sentence interpretation, rather than on their well-formedness. The results of these experiments are expected to contribute to our understanding of how the language system is organized, which is necessary before we can understand the basis of aphasic symptoms and how their remediation might be approached.
