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veitch-et-al-2021-a-narrow-ear-canal-reduces-sound-velocity-to-create-additional-acoustic-inputs-in-a-microscale-insect.pdf (1.47 MB)

A narrow ear canal reduces sound velocity to create additional acoustic inputs in a microscale insect ear

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journal contribution
posted on 2024-02-08, 16:16 authored by D Veitch, E Celiker, S Aldridge, C Pulver, CD Soulsbury, T Jonsson, C Woodrow, Z Fernando Montealegre
Located in the forelegs, katydid ears are unique among arthropods in having outer, middle, and inner components, analogous to the mammalian ear. Unlike mammals, sound is received externally via two tympanic membranes in each ear and internally via a narrow ear canal (EC) derived from the respiratory tracheal system. Inside the EC, sound travels slower than in free air, causing temporal and pressure differences between external and internal inputs. The delay was suspected to arise as a consequence of the narrowing EC geometry. If true, a reduction in sound velocity should persist independently of the gas composition in the EC (e.g., air, CO2). Integrating laser Doppler vibrometry, microcomputed tomography, and numerical analysis on precise three-dimensional geometries of each experimental animal EC, we demonstrate that the narrowing radius of the EC is the main factor reducing sound velocity. Both experimental and numerical data also show that sound velocity is reduced further when excess CO2 fills the EC. Likewise, the EC bifurcates at the tympanal level (one branch for each tympanic membrane), creating two additional narrow internal sound paths and imposing different sound velocities for each tympanic membrane. Therefore, external and internal inputs total to four sound paths for each ear (only one for the human ear). Research paths and implication of findings in avian directional hearing are discussed.

Funding

European Research Council Grant ERCCoG-2017-773067

European Commission via Horizon 2020 Marie Skłodowska-Curie Fellowship 829208 (InWingSpeak)

History

Author affiliation

School of Engineering, University of Leicester

Version

  • VoR (Version of Record)

Published in

Proceedings of the National Academy of Sciences of the United States of America

Volume

118

Issue

10

Pagination

e2017281118

Publisher

Proceedings of the National Academy of Sciences

issn

0027-8424

eissn

1091-6490

Copyright date

2021

Available date

2024-02-08

Spatial coverage

United States

Language

eng

Data Access Statement

Numerical simulations, experimental data (laser Doppler vibrometry recordings), Comsol model files, and μ -CT stereolithography files (in .stl format) are available in Dryad (DOI: 10.5061/dryad.2547d7wnn; deposited 8 November 2020).

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