The Integration of Parallel Processing Streams in the Sound Localization System of the Barn Owl

Abstract

The barn owl, Tyto alba, exhibits both peripheral and central nervous system specializations that enable it to accurately localize sounds in space. Interaural time difference (ITD), for azimuthal localization, and interaural level difference (ILD), for vertical localization, are computed in parallel by two independent pathways. These pathways remain anatomically and physiologically segregated up to the level of the lateral shell of the central nucleus of the inferior colliculus (LS). Electrophysiological mapping studies of the LS were performed to characterize the mechanisms underlying the convergence of the ITD and ILD processing streams. These studies suggest that the space specificity observed in the owl's auditory midbrain is an emergent property of a hierarchically organized feed-forward network arranged anatomically across the mediolateral extent of the LS.