Auditory brainstem models: adapting cochlear nuclei improve spatial encoding by the medial superior olive in reverberation

Andrew Brughera*, Jason Mikiel-Hunter, Mathias Dietz, David McAlpine

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

Abstract

Listeners typically perceive a sound as originating from the direction of its source, even as direct sound is followed milliseconds later by reflected sound from multiple different directions. Early-arriving sound is emphasised in the ascending auditory pathway, including the medial superior olive (MSO) where binaural neurons encode the interaural-time-difference (ITD) cue for spatial location. Perceptually, weighting of ITD conveyed during rising sound energy is stronger at 600 Hz than at 200 Hz, consistent with the minimum stimulus rate for binaural adaptation, and with the longer reverberation times at 600 Hz, compared with 200 Hz, in many natural outdoor environments. Here, we computationally explore the combined efficacy of adaptation prior to the binaural encoding of ITD cues, and excitatory binaural coincidence detection within MSO neurons, in emphasising ITDs conveyed in early-arriving sound. With excitatory inputs from adapting, nonlinear model spherical bushy cells (SBCs) of the bilateral cochlear nuclei, a nonlinear model MSO neuron with low-threshold potassium channels reproduces the rate-dependent emphasis of rising vs. peak sound energy in ITD encoding; adaptation is equally effective in the model MSO. Maintaining adaptation in model SBCs, and adjusting membrane speed in model MSO neurons, ‘left’ and ‘right’ populations of computationally efficient, linear model SBCs and MSO neurons reproduce this stronger weighting of ITD conveyed during rising sound energy at 600 Hz compared to 200 Hz. This hemispheric population model demonstrates a link between strong weighting of spatial information during rising sound energy, and correct unambiguous lateralisation of a speech source in reverberation.

Original languageEnglish
Pages (from-to)289-318
Number of pages30
JournalJARO - Journal of the Association for Research in Otolaryngology
Volume22
Issue number3
DOIs
Publication statusPublished - Jun 2021

Keywords

  • adaptation
  • cochlear nucleus
  • MSO
  • binaural
  • sensory coding
  • spatial hearing

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