Order and anomaly: An investigation of the semantic and syntactic contributions to sentence processing in the left and right cerebral hemispheres

This dissertation set out to examine hemispheric sensitivity to sentence-level constraints on meaning, and to discover how the processing of each hemisphere may contribute to the construction of an internal representation of the message conveyed by the sentence. In particular, I wanted to know to what extent the semantic and grammatical information conveyed by the sentence influences message level processing in the left and right hemispheres. The first experiment attempted to tease apart semantic, grammatical, and message-level processes by comparing normal sentences to sentences which had an anomalous sentence level meaning (but still contained a lexical-semantic associate), sentences where the syntactic information was removed by randomly rearranging the word order, and sentences in which all of the semantic information was removed by replacing content words with pseudowords, but leaving the sources of grammatical information intact (preserving function word order and inflections). Both hemispheres exhibited better performance for normal than for anomalous sentences, suggesting a bilateral sensitivity to message-level meaning. Surprisingly, the RH was also found to be sensitive to the syntactic structure of the sentence. The second experiment examined whether form-class constraints would mediate lexical-semantic priming during sentence comprehension. The LH was found to be much more sensitive to form-class constraints than was the RH. The third experiment looked at the importance of content and function word order, and found that the two hemispheres process word order information in qualitatively different ways. These results are discussed in terms of the theoretical implications for left and right hemisphere language functions, and potential models of right and left hemisphere sentence comprehension are described.