Understanding degraded speech leads to perceptual gating of a brainstem reflex in human listeners

PLoS Biol. 2021 Oct 20;19(10):e3001439. doi: 10.1371/journal.pbio.3001439. eCollection 2021 Oct.

Abstract

The ability to navigate "cocktail party" situations by focusing on sounds of interest over irrelevant, background sounds is often considered in terms of cortical mechanisms. However, subcortical circuits such as the pathway underlying the medial olivocochlear (MOC) reflex modulate the activity of the inner ear itself, supporting the extraction of salient features from auditory scene prior to any cortical processing. To understand the contribution of auditory subcortical nuclei and the cochlea in complex listening tasks, we made physiological recordings along the auditory pathway while listeners engaged in detecting non(sense) words in lists of words. Both naturally spoken and intrinsically noisy, vocoded speech-filtering that mimics processing by a cochlear implant (CI)-significantly activated the MOC reflex, but this was not the case for speech in background noise, which more engaged midbrain and cortical resources. A model of the initial stages of auditory processing reproduced specific effects of each form of speech degradation, providing a rationale for goal-directed gating of the MOC reflex based on enhancing the representation of the energy envelope of the acoustic waveform. Our data reveal the coexistence of 2 strategies in the auditory system that may facilitate speech understanding in situations where the signal is either intrinsically degraded or masked by extrinsic acoustic energy. Whereas intrinsically degraded streams recruit the MOC reflex to improve representation of speech cues peripherally, extrinsically masked streams rely more on higher auditory centres to denoise signals.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Acoustic Stimulation
  • Adolescent
  • Adult
  • Auditory Cortex / physiology
  • Behavior
  • Brain Stem / physiology*
  • Cochlea / physiology
  • Computer Simulation
  • Female
  • Humans
  • Male
  • Models, Biological
  • Neurons / physiology
  • Noise
  • Reflex / physiology*
  • Speech / physiology*
  • Speech Perception / physiology*
  • Task Performance and Analysis
  • Young Adult

Associated data

  • Dryad/10.5061/dryad.3ffbg79fw

Grants and funding

H.H.P. was supported in this study by an International Macquarie University Excellence Scholarship (https://www.mq.edu.au/research/phd-and-research-degrees/scholarships/scholarship-search/data/international-hdr-main-scholarship-round) and the The HEARing Cooperative Research Centre (https://www.hearingcrc.org/) J.M.H. was supported in this study by an Australian Research Council Laureate Fellowship (FL 160100108) awarded to D.M (https://www.arc.gov.au/grants/discovery-program/australian-laureate-fellowships).The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.