Auditory Functional Analysis: Lessons From the Primate Auditory Ossicles

Soon after the auditory structures were first described, mechanical engineering theory was applied in order to understand the movements of the various components and the forces generated during this process, with the aim to accurately postulate the actual hearing of an individual or species. Many acoustic hypotheses are limited by their assumption of perfect conditions or ideal movements and rely on the ossicular chain functioning as a mechanical lever unit, however, changes in the angles between these bones have not been considered and until such studies are conducted, the movements of the ossicular chain under sound pressure cannot be accurately modelled. To address this issue, a landmark analysis was conducted on ultra‐high resolution computer tomography (UhrCT) scans of twenty‐six primate auditory ossicle chains. The study allowed not only visualisation but quantification of unexpected angles between bones and articulations which may answer questions regarding ossicle flexibility and relative motions. The morphometry of stand‐out specimens including the articulation angle of V.v. variegata, the relatively large chain of Daubentonia, the bulbous and shortened chain of A. calabarensis and the mediolaterally constricted bodies of T. bancanus suggest that many of the foundational mechanical theories of the auditory system will need to be revised to include more variables than they currently accept. Grant Funding Source : NSERC discovery grant to MTS and the Canadian Research Chairs program for YC