title: The three-channel model of sound localization mechanisms: interaural level differences.
abstract: The current understanding of mammalian sound localization is that azimuthal (horizontal) position assignments are dependent upon the relative activation of two populations of broadly-tuned hemifield neurons with overlapping medial borders. Recent psychophysical work has provided evidence for a third channel of low-frequency interaural time difference (ITD)-sensitive neurons tuned to the azimuthal midline. However, the neurophysiological data on free-field azimuth receptive fields, especially of cortical neurons, has primarily studied high-frequency cells whose receptive fields are more likely to have been shaped by interaural level differences (ILDs) than ITDs. In four experiments, a selective adaptation paradigm was used to probe for the existence of a midline channel in the domain of ILDs. If no midline channel exists, symmetrical adaptation of the lateral channels should not result in a shift in the perceived intracranial location of subsequent test tones away from the adaptors because the relative activation of the two channels will remain unchanged. Instead, results indicate a shift in perceived test tone location away from the adaptors, which supports the existence of a midline channel in the domain of ILDs. Interestingly, this shift occurs not only at high frequencies, traditionally associated with ILDs in natural settings, but at low frequencies as well.
authors.affiliation: Department of Psychology and Neuroscience, Dalhousie University, 1355 Oxford Street, PO Box 15000, Halifax, NS B3H 4R2, Canada. rdingle@dal.ca
authors.forename: Rachel N
authors.initials: RN
authors.lastname: Dingle
authors.forename: Susan E
authors.initials: SE
authors.lastname: Hall
authors.forename: Dennis P
authors.initials: DP
authors.lastname: Phillips
mesh_terms: D000161:Acoustic Stimulation / Q000379:methods; D000328:Adult; D000704:Analysis of Variance; D006801:Humans; D007600:Judgment / Q000502:physiology; D008875:Middle Aged; D008954:Models, Biological; D010898:Pitch Perception / Q000502:physiology; D013017:Sound Localization / Q000502:physiology*; D013018:Sound Spectrography