title: Sound frequency-invariant neural coding of a frequency-dependent cue to sound source location.
abstract: The century-old duplex theory of sound localization posits that low- and high-frequency sounds are localized with two different acoustical cues, interaural time and level differences (ITDs and ILDs), respectively. While behavioral studies in humans and behavioral and neurophysiological studies in a variety of animal models have largely supported the duplex theory, behavioral sensitivity to ILD is curiously invariant across the audible spectrum. Here we demonstrate that auditory midbrain neurons in the chinchilla (Chinchilla lanigera) also encode ILDs in a frequency-invariant manner, efficiently representing the full range of acoustical ILDs experienced as a joint function of sound source frequency, azimuth, and distance. We further show, using Fisher information, that nominal "low-frequency" and "high-frequency" ILD-sensitive neural populations can discriminate ILD with similar acuity, yielding neural ILD discrimination thresholds for near-midline sources comparable to behavioral discrimination thresholds estimated for chinchillas. These findings thus suggest a revision to the duplex theory and reinforce ecological and efficiency principles that hold that neural systems have evolved to encode the spectrum of biologically relevant sensory signals to which they are naturally exposed.
authors.affiliation: Neuroscience Training Program, University of Colorado School of Medicine, Aurora, Colorado; and Department of Physiology and Biophysics, University of Colorado School of Medicine, Aurora, Colorado.
authors.forename: Heath G
authors.initials: HG
authors.lastname: Jones
authors.affiliation: Department of Physiology and Biophysics, University of Colorado School of Medicine, Aurora, Colorado.
authors.forename: Andrew D
authors.initials: AD
authors.lastname: Brown
authors.affiliation: Department of Physiology and Biophysics, University of Colorado School of Medicine, Aurora, Colorado.
authors.forename: Kanthaiah
authors.initials: K
authors.lastname: Koka
authors.affiliation: Neuroscience Training Program, University of Colorado School of Medicine, Aurora, Colorado; and Department of Physiology and Biophysics, University of Colorado School of Medicine, Aurora, Colorado.
authors.forename: Jennifer L
authors.initials: JL
authors.lastname: Thornton
authors.affiliation: Neuroscience Training Program, University of Colorado School of Medicine, Aurora, Colorado; and Department of Physiology and Biophysics, University of Colorado School of Medicine, Aurora, Colorado daniel.tollin@ucdenver.edu.
authors.forename: Daniel J
authors.initials: DJ
authors.lastname: Tollin
mesh_terms: D000161:Acoustic Stimulation; D000162:Acoustics; D000200:Action Potentials; D000818:Animals; D001306:Auditory Pathways / Q000502:physiology*; D002682:Chinchilla; D003463:Cues; D005260:Female; D007245:Inferior Colliculi / Q000502:physiology*; D007257:Information Theory; D008297:Male; D008839:Microelectrodes; D009474:Neurons / Q000502:physiology*; D013017:Sound Localization / Q000502:physiology*
keywords: inferior colliculus; interaural level difference; low-frequency neurons; sound localization