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.

Computational model of the human cochlea with motion of the layered osseous spiral lamina.

Purpose: In the base of the human cochlea, the partition anatomy is distinct from the commonly recognized anatomy of laboratory animals. The human features a radially wide, osseous spiral lamina (OSL) and a soft-tissue bridge region that connects the OSL to the basilar membrane proper. In addition to the basilar membrane, the human OSL and bridge move considerably.