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The Journal of Neuroscience, November 9, 2005, 25(45):10446-10461; doi:10.1523/JNEUROSCI.2093-05.2005

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Behavioral/Systems/Cognitive
Localization and Identification of Concurrent Sounds in the Owl's Auditory Space Map

Clifford H. Keller and Terry T. Takahashi

Institute of Neuroscience, University of Oregon, Eugene, Oregon 97403

In nature, sounds from multiple sources sum at the eardrums, generating complex cues for sound localization and identification. In this clutter, the auditory system must determine "what is where." We examined this process in the auditory space map of the barn owl's (Tyto alba) inferior colliculus using two spatially separated sources simultaneously emitting uncorrelated noise bursts, which were uniquely identified by different frequencies of sinusoidal amplitude modulation. Spatial response profiles of isolated neurons were constructed by testing the source-pair centered at various locations in virtual auditory space. The neurons responded whenever a source was placed within the receptive field, generating two clearly segregated foci of activity at appropriate loci. The spike trains were locked strongly to the amplitude modulation of the source within the receptive field, whereas the other source had minimal influence. Two sources amplitude modulated at the same rate were resolved successfully, suggesting that source separation is based on differences of fine structure. The spike rate and synchrony were stronger for whichever source had the stronger average binaural level. A computational model showed that neuronal activity was primarily proportional to the degree of matching between the momentary binaural cues and the preferred values of the neuron. The model showed that individual neurons respond to and synchronize with sources in their receptive field if there are frequencies having an average binaural-level advantage over a second source. Frequencies with interaural phase differences that are shared by both sources may also evoke activity, which may be synchronized with the amplitude modulations from either source.

Key words: auditory scene analysis; binaural; inferior colliculus; masking; sound localization; stream segregation

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Received May 24, 2005; revised September 23, 2005; accepted September 24, 2005.

This article has been cited by other articles:

				B. J. Fischer, J. L. Pena, and M. Konishi Emergence of Multiplicative Auditory Responses in the Midbrain of the Barn Owl J Neurophysiol, September 1, 2007; 98(3): 1181 - 1193. [Abstract] [Full Text] [PDF]

				H. Wagner, A. Asadollahi, P. Bremen, F. Endler, K. Vonderschen, and M. von Campenhausen Distribution of Interaural Time Difference in the Barn Owl's Inferior Colliculus in the Low- and High-Frequency Ranges J. Neurosci., April 11, 2007; 27(15): 4191 - 4200. [Abstract] [Full Text] [PDF]

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