# Auditory Processing of Complex Sounds

> **NIH NIH R01** · UNIVERSITY OF ROCHESTER · 2021 · $517,656

## Abstract

The challenge of understanding speech in noise, especially for listeners with sensorineural hearing loss
(SNHL), cannot be explained by conventional models of neural coding. These models are typically based on
average discharge rates and/or phase-locking to temporal fine structure of auditory-nerve (AN) fibers. Because
these response properties are only weakly affected by mild to moderate SNHL, such models fail to explain the
significant difficulties caused by relatively small amounts of hearing loss. Our recent studies of responses in
the midbrain of rabbit and budgerigar have directed our attention to response features that apparently solve
this problem. Midbrain neurons are well known to be strongly driven (or suppressed) by low-frequency
amplitude modulations (AM). We have recently observed that selectivity of midbrain neurons to the direction of
frequency chirps can match or exceed their AM sensitivity. Changes in amplitudes and frequencies of neural
responses across peripheral frequency channels create strong fluctuation contrasts that encode the location of
spectral peaks (formants) in voiced speech. We hypothesize that midbrain sensitivity to neural amplitude
and frequency fluctuations in peripheral responses provides a robust representation of complex
sounds, including speech. Aim 1 tests this hypothesis with physiological and behavioral studies of midbrain
responses to stimuli that combine these cues, including “designer” stimuli with conflicting cues to determine
how they may interact. These results will be used to test and refine a new computational model for midbrain
responses with sensitivity to these cues. Aim 2 tests the hypothesis with physiological responses of midbrain
neurons to voiced speech, to directly test model predictions based on characterization of each neuron's
sensitivity to these cues.
Understanding the role in speech coding of the amplitude and frequency fluctuations in peripheral
responses is clinically significant because these fluctuations are vulnerable to SNHL. In Aim 3, we will test
the hypothesis that amplitude and frequency fluctuations can be manipulated in synthetic speech to
influence intelligibility in human listeners with or without SNHL, in quiet and in noise. In the healthy
auditory system, fluctuation contrasts are mapped into a robust midbrain response, where rate and timing cues
(i.e., phase-locking to the F0-related fluctuations) persist across a wide range of sound levels and in noise.
Because fluctuation contrasts depend upon saturation of inner hair cells, which is in turn influenced by cochlear
amplification, pathological reduction of either inner or outer hair cell sensitivity reduces the fluctuation contrasts
in the periphery and ultimately in the midbrain. Model-based algorithms will manipulate the fluctuation contrasts
to improve (or degrade) intelligibility in listeners. Preliminary results from modeling, physiological, and
behavioral studies support the proposed hypotheses. Ultimately, ...

## Key facts

- **NIH application ID:** 10071079
- **Project number:** 5R01DC001641-30
- **Recipient organization:** UNIVERSITY OF ROCHESTER
- **Principal Investigator:** Laurel H. Carney
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2021
- **Award amount:** $517,656
- **Award type:** 5
- **Project period:** 1992-07-01 → 2023-11-30

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10071079

## Citation

> US National Institutes of Health, RePORTER application 10071079, Auditory Processing of Complex Sounds (5R01DC001641-30). Retrieved via AI Analytics 2026-05-23 from https://api.ai-analytics.org/grant/nih/10071079. Licensed CC0.

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