The function of the medial superior olive in small mammals: temporal receptive fields in auditory analysis |
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Authors: | B Grothe G Neuweiler |
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Institution: | (1) Zoological Institute of Ludwig-Maximilians-University Munich, Luisenstrasse 14, D-80333 München, Germany e-mail: neuweil@zi.biologie.uni-muenchen.de Fax: +49-89-5902450, DE |
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Abstract: | Traditionally, the medial superior olive, a mammalian auditory brainstem structure, is considered to encode interaural time
differences, the main cue for localizing low-frequency sounds. Detection of binaural excitatory and inhibitory inputs are
considered as an underlying mechanism. Most small mammals, however, hear high frequencies well beyond 50 kHz and have small
interaural distances. Therefore, they can not use interaural time differences for sound localization and yet possess a medial
superior olive. Physiological studies in bats revealed that medial superior olive cells show similar interaural time difference
coding as in larger mammals tuned to low-frequency hearing. Their interaural time difference sensitivity, however, is far
too coarse to serve in sound localization. Thus, interaural time difference sensitivity in medial superior olive of small
mammals is an epiphenomenon. We propose that the original function of the medial superior olive is a binaural cooperation
causing facilitation due to binaural excitation. Lagging inhibitory inputs, however, suppress reverberations and echoes from
the acoustic background. Thereby, generation of antagonistically organized temporal fields is the basic and original function
of the mammalian medial superior olive. Only later in evolution with the advent of larger mammals did interaural distances,
and hence interaural time differences, became large enough to be used as cues for sound localization of low-frequency stimuli.
Accepted: 28 February 2000 |
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Keywords: | Medial superior olive Interaural time difference Receptive field Precedence effect Temporal processing |
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