A narrow ear canal reduces sound velocity to create additional acoustic inputs in a micro-scale insect ear

Veitch, Daniel, Celiker, Emine, Aldridge, Sarah , Pulver, Christian Adlai, Soulsbury, Carl, Jonsson, Thorin, Woodrow, Charlie and Montealegre-Z, Fernando (2021) A narrow ear canal reduces sound velocity to create additional acoustic inputs in a micro-scale insect ear. Proceedings of the National Academy of Sciences, 118 (10). e2017281118. ISSN 0027-8424

Full content URL: https://doi.org/10.1073/pnas.2017281118

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A narrow ear canal reduces sound velocity to create additional acoustic inputs in a micro-scale insect ear
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A narrow ear canal reduces sound velocity to create additional acoustic inputs in a micro-scale insect ear
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Abstract

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, micro-CT scanning, and numerical analysis on precise 3D 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). New research paths, and implication of findings in avian directional hearing are discussed.

Keywords:Bioacoustics, Katydid hearing, sound propagation, finite element analysis
Subjects:C Biological Sciences > C770 Biophysical Science
G Mathematical and Computer Sciences > G140 Numerical Analysis
F Physical Sciences > F361 Laser Physics
F Physical Sciences > F380 Acoustics
C Biological Sciences > C340 Entomology
Divisions:College of Science > School of Life Sciences
ID Code:43806
Deposited On:15 Feb 2021 16:09

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