| Abstract: | Barn owls localize sound by using the interaural time difference of the horizontal plane and the interaural intensity difference for the vertical plane. The owl's auditory system possesses the two binaural cues in separate pathways in the brainstem. Owls use a process similar to cross-correlation to derive interaural time differences. Convergence of different frequency bands in the inferior colliculus solves the problems of phase-ambiguity which is inherent in cross-correlating periodic signals. The two pathways converge in the external nucleus of the inferior colliculus to give rise to neurons that are selective for combinations of the two cues. These neurons form a map of auditory space. The map projects to the optic tectum to form a bimodal map which, in turn, projects to a motor map for head turning. The visual system calibrates the auditory space map during ontogeny in which acoustic variables change. In addition to this tectal pathway, the forebrain can also control the sound-localizing behaviour. |
