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Spatial Selectivity and Binaural Responses in the Inferior Colliculus of the Great Horned Owl

Volman, Susan F. and Konishi, Masakazu (1989) Spatial Selectivity and Binaural Responses in the Inferior Colliculus of the Great Horned Owl. Journal of Neuroscience, 9 (9). pp. 3083-3096. ISSN 0270-6474. http://resolver.caltech.edu/CaltechAUTHORS:20151202-075715738

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Abstract

In this study we have investigated the processing of auditory cues for sound localization in the great horned owl (Bubo virginianus). Previous studies have shown that the barn owl, whose ears are asymmetrically oriented in the vertical plane, has a 2-dimensional, topographic representation of auditory space in the external division of the inferior colliculus (ICx). As in the barn owl, the great horned owl's ICx is anatomically distinct and projects to the optic tectum. Neurons in ICx respond over only a small range of azimuths (mean = 32 degrees), and azimuth is topographically mapped. In contrast to the barn owl, the great horned owl has bilaterally symmetrical ears and its receptive fields are not restricted in elevation. The binaural cues available for sound localization were measured both with cochlear microphonic recordings and with a microphone attached to a probe tube in the auditory canal. Interaural time disparity (ITD) varied monotonically with azimuth. Interaural intensity differences (IID) also changed with azimuth, but the largest IIDs were less than 15 dB, and the variation was not monotonic. Neither ITD nor IID varied systematically with changes in the vertical position of a sound source. We used dichotic stimulation to determine the sensitivity of ICx neurons to these binaural cues. Best ITD of ICx units was topographically mapped and strongly correlated with receptive-field azimuth. The width of ITD tuning curves, measured at 50% of the maximum response, averaged 72 microseconds. All ICx neurons responded only to binaural stimulation and had nonmonotonic IID tuning curves. Best IID was weakly, but significantly, correlated with best ITD (r = 0.39, p less than 0.05). The IID tuning curves, however, were broad (mean 50% width = 24 dB), and 67% of the units had best IIDs within 5 dB of 0 dB IID. ITD tuning was sensitive to variations in IID in the direction opposite to that expected for time-intensity trading, but the magnitude of this effect was only 1.5 microseconds/dB IID. We conclude that, in the great horned owl, the spatial selectivity of ICx neurons arises primarily from their ITD tuning. Except for the absence of elevation selectivity and the narrow range of best IIDs, ICx in the great horned owl appears to be organized much the same as in the barn owl.


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http://www.jneurosci.org/content/9/9/3083.shortPublisherArticle
Additional Information:© 1989 by Society for Neuroscience. For the first six months after publication SfN’s license will be exclusive. Beginning six months after publication the Work will be made freely available to the public on SfN’s website to copy, distribute, or display under a Creative Commons Attribution 4.0 International (CC BY 4.0) license (https://creativecommons.org/licenses/by/4.0/). Received Oct. 31, 1988; revised Feb. 10, 1989; accepted Feb. 28, 1989. We thank R. Adolphs, S. Esterly, I. Fujita, E. Knudsen, J. Olsen, and T. Takahashi for their comments on the manuscript, and T. Takahashi, H. Wagner, and C E. Carr for their advice, assistance, and helpful discussions throughout the work. We are also grateful to the following people: M. Zucker for artwork; Dr. D. E. M. Lawson for providing the primary antiserum for calbindin immunohistochemistry; and Drs. D. Van Essen and J. Allman, whose facilities we used for computer microscopy and 3-D reconstructions. This work was supported by NRSA Fellowship NS07714 (to S.F.V.) and NSF Grant BNS8411458 (to M.K.).
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Funding AgencyGrant Number
NRSA FellowshipNS07714
NSFBNS8411458
Record Number:CaltechAUTHORS:20151202-075715738
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:20151202-075715738
Official Citation:Spatial selectivity and binaural responses in the inferior colliculus of the great horned owl SF Volman and M Konishi The Journal of Neuroscience, 1 September 1989, 9(9):3083-3096
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:62527
Collection:CaltechAUTHORS
Deposited By: Ruth Sustaita
Deposited On:02 Dec 2015 21:14
Last Modified:02 Dec 2015 23:37

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