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Published September 1, 1998 | Published
Journal Article Open

How the owl resolves auditory coding ambiguity

Abstract

The barn owl (Tyto alba) uses interaural time difference (ITD) cues to localize sounds in the horizontal plane. Low-order binaural auditory neurons with sharp frequency tuning act as narrow-band coincidence detectors; such neurons respond equally well to sounds with a particular ITD and its phase equivalents and are said to be phase ambiguous. Higher-order neurons with broad frequency tuning are unambiguously selective for single ITDs in response to broad-band sounds and show little or no response to phase equivalents. Selectivity for single ITDs is thought to arise from the convergence of parallel, narrow-band frequency channels that originate in the cochlea. ITD tuning to variable bandwidth stimuli was measured in higher-order neurons of the owl's inferior colliculus to examine the rules that govern the relationship between frequency channel convergence and the resolution of phase ambiguity. Ambiguity decreased as stimulus bandwidth increased, reaching a minimum at 2–3 kHz. Two independent mechanisms appear to contribute to the elimination of ambiguity: one suppressive and one facilitative. The integration of information carried by parallel, distributed processing channels is a common theme of sensory processing that spans both modality and species boundaries. The principles underlying the resolution of phase ambiguity and frequency channel convergence in the owl may have implications for other sensory systems, such as electrolocation in electric fish and the computation of binocular disparity in the avian and mammalian visual systems.

Additional Information

© 1998 National Academy of Sciences. Edited by Masakazu Konishi, California Institute of Technology, Pasadena, CA, and approved July 17, 1998 (received for review June 3, 1998). I thank Drs. Mike Lewicki, David Perkel, Terry Takahashi, Koichi Mori, and Kourosh Saberi for numerous valuable discussions and important critical comments on this manuscript. This work was supported by National Institute of Neurological Disorders and Stroke Grant DC-00134. This paper was submitted directly (Track II) to the Proceedings office. The publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked ''advertisement'' in accordance with 18 U.S.C. §1734 solely to indicate this fact.

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