Sound transmission by the hyoid apparatus during echolocation in bats
Chelsie C.G. Snipes1 and Richard T. Carter1
1 East Tennessee State University, Johnson City TN, USA
The morphology of the stylohyal-tympanic bone articulation found in laryngeally echolocating bats is highly indicative of a function associated with signal production. One untested hypothesis is that this morphology allows the transfer of a sound signal from the larynx to the tympanic bones (auditory bulla) via the hyoid apparatus during signal production by the larynx. To test this hypothesis, we used µCT data, CAD editing software, and finite element analysis (FEA) to model the propagation of sound through the hyoid chain into the tympanic bones. This involved making digital segmentations from the µCT data of the tympanic bones and cartilaginous segments and converting it into a digital mesh body. Since the cartilaginous segments are not visible in CTs, we segmented the air in each gap and subsequently used a Boolean function in CAD software to fit each bony end into their respective cartilaginous segment. Further post-processing of the model included a reduction in the number of facets bodies and smoothing surfaces which allowed us to convert it into a solid body model. The solid body geometry was then uploaded into FEA software and assigned material properties for cortical bone, cartilage, and bulla. Additional biomechanical data, including Young’s Modulus, Poisson’s ratio, and speed of sound through each material were defined in previous literature. We ran two FEA analysis with our model: the first was an acoustic analysis that modelled sound propagation through our material (bone and cartilage), and the second was a coupled modal and structural analysis that modelled resonant behavior and sound pressure wave propagation from the hyoid body to the tympanic bones. Our models support the hypothesis that bats use this physical connection between the larynx and auditory bulla to transfer sound (mechanical excitation). Our models show both pressure waves and vibration due to resonance could be used to transfer this signal and this resonance behavior can be modulated by restraining the hyoid apparatus, perhaps through muscle contraction. We propose that by modulating the resonant behavior of the hyoid apparatus, bats can selectively filter which frequencies of sound are transferred from the larynx to the auditory bulla during echolocation signal production.
| Identifer | oai:union.ndltd.org:ETSU/oai:dc.etsu.edu:asrf-1781 |
| Date | 18 March 2021 |
| Creators | Snipes, Chelsie, Carter, Richard T |
| Publisher | Digital Commons @ East Tennessee State University |
| Source Sets | East Tennessee State University |
| Detected Language | English |
| Type | text |
| Source | Appalachian Student Research Forum |
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