Auditory processing of spectral cues for sound localization in the inferior colliculus

Kevin A. Davis, Ramnarayan Ramachandran, Bradford J. May

Research output: Contribution to journalArticle

Abstract

The head-related transfer function (HRTF) of the cat adds directionally dependent energy minima to the amplitude spectrum of complex sounds. These spectral notches are a principal cue for the localization of sound source elevation. Physiological evidence suggests that the dorsal cochlear nucleus (DCN) plays a critical role in the brainstem processing of this directional feature. Type O units in the central nucleus of the inferior colliculus (ICC) are a primary target of ascending DCN projections and, therefore, may represent midbrain specializations for the auditory processing of spectral cues for sound localization. Behavioral studies confirm a loss of sound orientation accuracy when DCN projections to the inferior colliculus are surgically lesioned. This study used simple analogs of HRTF notches to characterize single-unit response patterns in the ICC of decerebrate cats that may contribute to the directional sensitivity of the brain's spectral processing pathways. Manipulations of notch frequency and bandwidth demonstrated frequency-specific excitatory responses that have the capacity to encode HRTF-based cues for sound source location. These response patterns were limited to type O units in the ICC and have not been observed for the projection neurons of the DCN. The unique spectral integration properties of type O units suggest that DCN influences are transformed into a more selective representation of sound source location by a local convergence of wideband excitatory and frequency-tuned inhibitory inputs.

Original languageEnglish (US)
Pages (from-to)148-163
Number of pages16
JournalJARO - Journal of the Association for Research in Otolaryngology
Volume4
Issue number2
DOIs
StatePublished - Jun 2003

Keywords

  • Central nucleus
  • Dorsal cochlear nucleus
  • Head-related transfer function
  • Sound localization
  • Spectral integration

ASJC Scopus subject areas

  • Otorhinolaryngology
  • Sensory Systems

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