9507924 HELLIGE The goal of cognitive neuroscience is to understand how it is that our brains produce our thoughts, our emotions and our actions. A pervasive characteristic of the human brain is what has been termed cerebral hemisphere asymmetry. The cerebral cortex (or outside surface) of the brain is divided into two hemispheres, the right and the left. Although their gross appearance is very similar, there are subtle differences in the anatomical structure of the two hemispheres and in their information processing abilities and propensities. This research will investigate the consequences of this hemispheric specialization for information processing in neurologically normal individuals in several specific areas of functioning. One set of studies will increase our understanding of hemispheric specialization for processing spatial relationships by investigating visual mechanisms that underlie the tendency of the two hemispheres to make different contributions to processing what have been called categorical (e.g., above/ below, left/right, etc.) and coordinate (e.g., distance between two objects) aspects of spatial location. A second set of studies will determine the extent to which the same visual mechanisms also contribute to hemispheric differences in the identification of visual stimuli, including letters, words and other multipart objects (e.g., an airplane). In order to understand how it is that the two hemispheres make complementary contributions to perception, cognition and action, it is important to understand the ways in which the two hemispheres interact with each other to coordinate their activities and produce unified effects on behavior. For this reason, a third set of studies will examine interhemispheric interaction for the processing of both verbal and nonverbal information, with an emphasis on tasks that are known to be performed in qualitatively different ways by the left and right hemispheres. It is also impossible to understand the role that hemispheric asymmetry plays in normal cognitive processing without understanding the role that such asymmetry plays in individual variation. With this in mind, a fourth set of studies will focus on differences from person to person in the pattern of hemispheric asymmetry and in the nature and efficiency of interhemispheric interaction. Some of these studies will also determine the relationship between various functional or behavioral asymmetries and anatomical/structural brain asymmetries as determined by brain imaging procedures. Each set of studies will address basic issues in cognitive neuroscience. At the same time, the outcomes will have implications for a variety of more applied questions. For example, it has been hypothesized that a variety of disorders (e.g., dyslexia,) result from unusual patterns of hemispheric asymmetry or from difficulty in coordinating the activities of the two hemispheres. Testing such hypotheses requires detailed information about the normal patterns of operation of the two hemispheres, separately and in concert. ***
