# Neural and Perceptual Mechanisms for Coding Frequency Modulation

> **NIH NIH R21** · UNIVERSITY OF MICHIGAN AT ANN ARBOR · 2024 · $127,282

## Abstract

Modulations in frequency and amplitude are fundamental attributes of natural sounds. Frequency modulation
(FM) is essential for sound segregation, talker recognition, and the tracking of prosody in speech and music.
FM sensitivity degrades with normal aging and hearing loss, thereby restricting the communication abilities of
older and hearing-impaired individuals. Importantly, assistive listening devices, such as hearing aids and
cochlear implants, have not been successful in restoring FM sensitivity. This limitation is in part due to an
incomplete understanding of the neural and perceptual mechanisms underlying FM coding. Human FM
perception is best at the low rates (fm < ~5-10 Hz) and carrier frequencies (fc < 4-5 kHz) that are also most
relevant for speech and music, with sensitivity worsening at faster rates and/or higher carriers. These rate and
carrier-dependent trends are widely believed to reflect dual mechanisms for FM coding: one mechanism based
on precise phase-locking to temporal fine structure (TFS; time code), and another based on the fidelity of
cochlear filtering across the tonotopic axis and amplitude modulation (AM) processing (envelope/place code).
Crucially, slow-rate, low-carrier FM has been treated as the gold standard behavioral measure for monaural
TFS coding. The proposed research will use a combination of psychoacoustics, computational modeling, and
electroencephalography (EEG) to test the hypothesis that neural and perceptual FM sensitivity in normal-
hearing listeners can instead be explained by a unitary neural place code. Aim 1 will provide new insights into
the necessity of time coding in FM detection in young, normal-hearing listeners by testing whether classic
behavioral evidence for time coding is also found when using novel amplitude-modulated stimuli that provide
no TFS cues. Aim 2 uses a rigorous, large-scale approach to test whether perceptual and neural degradations
in slow FM processing with age can be accounted for by TFS coding, as currently believed, or whether these
changes too can be explained within the unified framework based on place coding. This aim has important
clinical implications, as it provides the first large-scale replication and extension of a new EEG measure, the
FM following response (FMFR), which has been claimed to reflect individual fidelity of TFS coding to slow FM.
The results will provide the preliminary data and foundation for future studies with hearing-impaired listeners to
determine how these critical acoustic cues are affected by different types and degrees of hearing loss and how
both perceptual and neural responses can be explained within a unifying theoretical framework in order to
provide a novel basis for future sensory interventions.

## Key facts

- **NIH application ID:** 11222335
- **Project number:** 7R21DC019409-04
- **Recipient organization:** UNIVERSITY OF MICHIGAN AT ANN ARBOR
- **Principal Investigator:** Kelly L Whiteford
- **Activity code:** R21 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2024
- **Award amount:** $127,282
- **Award type:** 7
- **Project period:** 2021-12-01 → 2025-11-30

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/11222335

## Citation

> US National Institutes of Health, RePORTER application 11222335, Neural and Perceptual Mechanisms for Coding Frequency Modulation (7R21DC019409-04). Retrieved via AI Analytics 2026-05-22 from https://api.ai-analytics.org/grant/nih/11222335. Licensed CC0.

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