Abstract: Estimation of audiograms for marine mammals, particularly cetaceans, is a challenging task due to regulatory restrictions, sample availability, and the general paucity of data regarding the anatomical and physiological characteristics of the auditory system in these species. At present, we are characterizing point stiffness of the basilar membrane (BM), the principal resonating structure in the cochlea that supports hair cells of the organ of Corti. The ultimate goal of this project is to correlate point-stiffness measurements with accurate position-based estimates of the frequency response distribution along the BM in multiple cetacean species. Herein, we present the preliminary step of a method for estimating the length along the BM at which point-stiffness measurements were taken to determine frequency-stiffness correlates in one species, the harbor porpoise (Phocoena phocoena), which is also a “control” species for which there are live animal audiograms. A species-specific model of cochlear geometries and BM spirals were aligned and fitted to the individual curvature of each specimen on high-resolution photographs of the experimental point-stiffness measurement sites. This method produces reliable estimates of the location along the BM at which point stiffnesses were recorded, with precisions of approximately 0.33%, providing a reliable means of localizing point-stiffness responses for improving audiogram estimation.
Key Words: cetacean, hearing, modeling, basilar membrane, frequency-place map, cochlear length
DOI: https://doi.org/10.1578/AM.45.6.2019.733
Page Numbers: 733-738

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