Physiological mechanisms of three-dimensional hearing.

Abstract

1. Bilateral cold blocking of the temporal regions of the cortex in cats, causing temporary disappearance of hearing, does not disturb spatial differentiation formed previously, evidence that localization of sound can take place through the activity of subcortical auditory formations. 2. Unilateral blocking of areas AI, AII, Ep, and IT, creating functional asymmetry at subcortical levels also irreversibly distorts the activity of binaural mechanisms, the normal working of which requires initial functional equilibrium of the paired auditory formations at all levels. 3. Unilateral blocking of area AI, as a result of the onset chiefly of only interhemispheric asymmetry, disturbs the localization of long sounds but does not prevent spatial discrimination of clicks. This confirms the view that the urgent orienting reaction to sound is subcortical in origin. 4. Sound is localized by all levels of the brain: Its distortion at lower levels leads to corresponding distortion at higher levels also. However, the decisive role in sound projection rests with the highest levels of the auditory system. 5. Animals with the cortical representation of hearing intact in only one hemisphere can project sound only into the field opposite to the intact hemisphere, and only on the conventional prolongation of the interaural line. 6. In the course of evolution animals evidently acquire several mechanisms of sound localization, and a new and more perfect mechanism formed at a certain stage does not lead to disappearance of the previous mechanisms, but incorporates them in itself as subsystems and integrates the preliminary results of their activity.