# Ossicular Mechanics of a Low Frequency Ear and Implications for Bone-Conducted Hearing.

> **NIH NIH K01** · MASSACHUSETTS EYE AND EAR INFIRMARY · 2020 · $141,750

## Abstract

Abstract
The mammalian ear contains three middle-ear bones called ossicles that transmit both air-conducted (AC)
sound from the eardrum to the inner ear and bone-conducted (BC) vibrations of the skull to the inner ear. The
functional significance of having three ossicles to transmit sound is not completely understood, yet their
varied shapes, mass distributions, and articulation around two flexible joints could serve to protect the inner
ear from static pressure and impulsive AC sounds presented in the ear canal, and could reduce sensitivity to
potentially distracting self-generated BC vibrations caused by head movement, chewing, etc. At the same
time, ossicles might also improve AC and BC hearing at low frequencies. In this study, we propose to test the
role that ossicular shape, mass and mass distribution, as well as flexibility play on 3D ossicular motion and
sound transmission into the cochlea for both human and elephant temporal bones in response to AC and BC
stimulation under normal and modified conditions. Despite significant anatomical differences, humans and
elephants exhibit very similar audiograms over their overlapping 20 Hz–11 kHz frequency range, although
elephants can hear below 20 Hz and humans can hear above 11 kHz. Middle-ear bones scale with skull size,
such that elephant ossicles (the largest among terrestrial mammals) are approximately seven times heavier
than those of humans. Studies suggest that BC hearing is enhanced below 100 Hz using mass-loading to
simulate greater ossicular mass, and our preliminary measurements on elephants suggest that their heavier
ossicles should yield an order of magnitude better BC hearing than humans at low frequencies. BC hearing in
elephants might also be enhanced due to what appears to be a partially fused incudo-malleolar joint. Thus,
quantifying the structure–function relationships and mass loading within human versus elephant ears could
improve our understanding of the possible optimizations and trade-offs within the middle ear. The immediate
goal of this investigation is to quantitatively compare human and elephant ossicular-chain morphology and
motion as it relates to input to the cochlea by measuring ossicular shape and mass distributions using µCT
imaging; and measuring 3D ossicular motions in response to AC and BC stimulation using 3D laser Doppler
vibrometry, for the normal and modified cases with added mass and reduced ossicular-joint flexibility. The
motion measurements will be used to animate µCT reconstructions of the ossicles, and these results will be
compared using moments of inertia (MOI) to quantify the functional implications of the inter-species structural
differences and effects of modifications in terms of: 1) sound transmission from the ear canal to the cochlea,
especially at lower frequencies; 2) the relative motion of the ossicles; and 3) the transmission of sound via
bone conduction. The structure–function relationships revealed through this inter-species comparison ...

## Key facts

- **NIH application ID:** 9869878
- **Project number:** 5K01DC017812-02
- **Recipient organization:** MASSACHUSETTS EYE AND EAR INFIRMARY
- **Principal Investigator:** Caitlin O'Connell-Rodwell
- **Activity code:** K01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2020
- **Award amount:** $141,750
- **Award type:** 5
- **Project period:** 2019-04-01 → 2024-03-31

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/9869878

## Citation

> US National Institutes of Health, RePORTER application 9869878, Ossicular Mechanics of a Low Frequency Ear and Implications for Bone-Conducted Hearing. (5K01DC017812-02). Retrieved via AI Analytics 2026-05-22 from https://api.ai-analytics.org/grant/nih/9869878. Licensed CC0.

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