A mystery solved: human high-frequency middle-ear motion

The middle ear transforms sound from low-impedance external air to high-impedance cochlear fluid. However, the human stapes – the input to the cochlea – has been reported to have minimal or no motion above ~ 4 kHz. For decades, this lack of observed high-frequency stapes motion has been puzzling, as it is inconsistent with our ability to hear up to 20 kHz. In this study we address this mysterious discrepancy. Here, we succeed in measuring robust high-frequency stapes motion up to 20 kHz in fresh human cadaveric ears. Furthermore, when stapes motion is robust at high frequencies, these ears also show robust cochlear partition motion measured in situ . The ability to measure robust high-frequency stapes and cochlear motion represents an advancement in the field. To preserve high-frequency sound transmission, we modify surgical technique to prevent loosening of the ossicular chain. This implies that similar modifications in otologic surgery for patients may better preserve high-frequency hearing. The importance of this is that the ability to understand speech in noisy environments and sound localization requires high-frequency hearing.