Binaural characteristics of units in the owl's brainstem auditory pathway: precursors of restricted spatial receptive fields.

The barn owl uses binaural phase and intensity differences for sound localization. These two cues also determine the receptive fields of specialized neurons in the inferior colliculus. The main aim of this study was to investigate where neuronal sensitivity to the binaural cues emerges in the brainstem auditory nuclei, and how this sensitivity reaches the neurons in the inferior colliculus. The owl's phase-sensitive neurons are selective to microsecond phase differences of high frequency signals, unlike mammalian phase-sensitive neurons which are restricted to low frequency signals. In certain nuclei virtually all of the neurons are sensitive to either phase differences or intensity differences, but not to both. These nuclei form two distinctly separate pathways that converge at the inferior colliculus where neurons selective to both phase and intensity differences occur. In contrast to the mammalian auditory system, the owl's phase- and intensity difference-sensitive pathways are not segregated into low frequency and high frequency channels.