A narrow ear canal reduces sound velocity to create additional acoustic inputs in a microscale insect ear
| Autor: | Charlie Woodrow, Carl D. Soulsbury, Christian Adlai Pulver, Daniel Veitch, Fernando Montealegre-Z, Emine Celiker, Sarah Aldridge, Thorin Jonsson |
|---|---|
| Rok vydání: | 2021 |
| Předmět: |
Human ear
Tympanic Membrane Bioacoustics 030310 physiology Acoustics education finite element analysis Gryllidae bioacoustics 03 medical and health sciences 0302 clinical medicine Hearing medicine otorhinolaryngologic diseases Animals Ear canal Sound (geography) Microscale chemistry Physics 0303 health sciences geography sound propagation Multidisciplinary geography.geographical_feature_category katydid hearing Animal Structures Radius Laser Doppler velocimetry Biological Sciences Experimental animal Biophysics and Computational Biology medicine.anatomical_structure sense organs 030217 neurology & neurosurgery Ear Canal |
| Zdroj: | Proceedings of the National Academy of Sciences of the United States of America Proceedings of the National Academy of Sciences |
| ISSN: | 1091-6490 |
| Popis: | Significance The katydid tympanal ears have outer, middle, and inner ear components analogous to mammalian ears. Unlike mammals, each ear has two tympana exposed to sound both externally and internally, with a delayed internal version arriving via the gas-filled ear canal (EC). The two combined inputs in each ear play a significant role in directional hearing. Here, we demonstrate that the major factor causing the internal delay is the EC geometry. The EC bifurcates asymmetrically, producing two additional internal paths that impose different sound velocities for each tympanum. Therefore, various versions of the same signal reach the ears at various times, increasing the chance to pinpoint the sound source. Findings could inspire algorithms for accurate acoustic triangulation in detection sensors. 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. |
| Databáze: | OpenAIRE |
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