The left and right hemispheres of the human cortex are specialized for different cognitive functions. This research will investigate the consequences of this specialization for information processing in neurologically normal individuals. The left hemisphere appears to be specialized for the processing of verbal and phonetic information; one set of studies will explore consequences of this left-hemisphere verbal/phonetic superiority. Other studies will test the hypothesis that the brain computes two types of spatial representations, one (computed by the left hemisphere) that is appropriate for categorizing locations (e.g., one stimulus is above another) and another (computed by the right hemisphere) that is appropriate for processing information about distance (e.g., two stimuli are more than 2 cm apart). The research will also investigate the manner in which unified information processing emerges from a brain consisting of two separate but interacting hemispheres. Of particular importance is the investigation of conditions that determine when the mode or style of processing characteristic of one hemisphere dominates performance. The research is designed around an experimental paradigm that allows a comparison of the style of cognitive processing when both hemispheres are stimulated at the same time to the styles of processing that are obtained when each individual hemisphere is stimulated separately. Individuals differ in their patterns of hemispheric superiority and it is likely that they also differ with respect to which hemisphere's preferred style of processing emerges when both hemispheres are equally stimulated. The research will investigate this by having the same individuals participate in a number of tasks chosen to measure different aspects of hemispheric asymmetry and interaction, to discover how performance on one task relates to performance on others. Although the research will address basic issues in human cognition, the outcome will have implications for a variety of important societal concerns. For example, many educators and scientists have held that individual differences in hemispheric asymmetry are related to a variety of learning disabilities such as dyslexia and attentional deficit disorder. Testing such notions has been nearly impossible because of the absence of noninvasive behavioral techniques to separate differences in hemispheric asymmetry from differences in the tendency to rely more on the processing style of one hemisphere or the other. The techniques developed in this research should make it possible to begin such testing, thus opening the door to answering a host of questions of great immediate practical import to our society.
