This proposal is part of a research program that aims to clarify (1) hemispheric specialization and independence. (2) interhemispheric spheric interaction, and (3) interhemispheric control. These mechanisms of interhemispheric relations address three central theoretical concepts in cognitive neuroscience: modularity of processing. intermodular communication. and behavior. Specific Aims A basic thesis of this research program is that the two cerebral hemispheres constitute parallel, semi-independent. information processing systems which interact through function-specific cortical channels in the corpus and through less specific subcortical channels. In the following proposal we analyze the anatomical basis of the relationship between hemispheric specialization and interhemispheric interaction by analyzing the anatomical substrates of language gifted asymmetric cortex and of the callosal channels that interconnect it. We focus on two regions corresponding to two of our main behavioral tasks; Broca's area, which is specialized for phonetic processing in dichotic listening to nonsense consonant-vowel syllables (CVs) and; Wernicke's area, which is specialized for lateralized lexical decision. Since we believe that the different behavioral measures draw upon these different cortical regions, we hypothesize that different behavioral measures will also be associated with different callosal channels. Furthermore, we expect the anatomical asymmetry of cortical modules will be negatively correlated with the size of the callosal channel that interconnects it. Another goal is to map the organization of callosal channels and their relationship to hemispheric specialization.