Modulating Cerebral Asymmetries for Language

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The cortex of the human brain is subdivided into two halves, the left and right hemispheres, which process information in characteristically different ways. Although it is acknowledged that nearly all mental activities require some contribution from each cerebral hemisphere, understanding when and how each system participates in a variety of cognitive tasks remains a significant scientific challenge. The long-term goal of this research is to determine the precise contributions of the left and right hemispheres when people comprehend words. The experiments will test the hypothesis that the relative participation of each hemisphere in word recognition is determined by the linguistic context in which a word is experienced, rather than by intrinsic characteristics of the word itself. Words will be presented in the left or right visual fields, thereby selectively stimulating the right or left hemisphere. Two important word properties will be investigated: grammatical class (noun vs verb) and concreteness of meaning (concrete vs abstract). It is predicted that the right cerebral hemisphere will make a greater contribution to recognizing nouns and concrete words in the context of verbs or abstract words, than in more homogeneous contexts. Such findings would suggest that cerebral asymmetries for word recognition vary dynamically in concert with variation in the stimulus environment, rather than reflecting static (and hence unmodifiable) processing differences. This research will indicate the extent to which context modulates the brain systems used to recognize words, thereby enhancing our understanding of the neural bases for language comprehension.