ELECTRIC RESPONSES OF THE BRAIN STEM TO BILATERAL AUDITORY STIMULATION

Abstract

When the 2 ears were stimulated alternately by 2 carefully matched sound systems, responses from the homolateral and contralateral components in the lateral lemniscus were practically equivalent in threshold, latency, and amplitude. Clicks and tones were used as stimuli. When both ears were stimulated simultaneously (at intensities less than 40 db above the threshold for either ear), the binaural latency was not appreciably shorter than either monaural latency; and binaural masking was not demonstrable; stimulation of both ears gave amplitudes expected from addition of the 2 monaural effects at low intensity levels (less than 10-15 db above threshold), but not at higher intensities. Binaural responses to tones gave perfect synchronization of homolateral with contralateral fibres. These results argued against the convergence of the tracts from the 2 ears in the cochlear nuclei or sup. olivary complex. When one ear was stimulated slightly before the other, both responses appeared in the record from the lateral lemniscus with the time difference preserved. The 2nd response showed no diminution in amplitude. These results were of significance for the problems of binaural interaction and auditory localization.