The objective of the proposed research is to investigate the anatomical basis for binaural hearing in insectivores and prosimian primates. The purpose of these comparative observations is to: (1) provide data relevant to the evolution of hearing in mammals and (2) provide an anatomical basis for behavioral studies on binaural hearing and auditory localization. In the anatomical studies, modern techniques for demonstrating connectivity in the nervous system are used to show ascending projections from the cochlear nucleus and superior olivary complex to inferior colliculus and descending connections from auditory cortex to inferior colliculus. The results of these anatomical experiments have provided specific hypotheses about the function of various parts of the central auditory system. Some of these hypotheses will be tested in behavioral experiments by examining the effects of lesions in subdivisions of the auditory pathway on auditory discriminations, especially localization of sound in space. BIBLIOGRAPHIC REFERENCES: Casseday, J. H., Diamond, I. T., and Harting, J. K. Auditory pathways to the cortex in Tupaia glis. J. Comp. Neurol, 1976, 166: 303-340. Neff, W. D. and Casseday, J. H. Effects of unilateral ablation of auditory cortex on monaural cat's ability to localize sound. J. Neurophysiol., 1977, 40:44-52.