Cochlea a protein motor called prestin on their outer membranes; it generates additional movement that couples back to the fluid–membrane wave. This "active amplifier" is essential in the ear's ability to amplify weak sounds. The active amplifier also leads to the phenomenon of soundwave vibrations being emitted from the cochlea back into the ear canal through the middle ear (otoacoustic emissions). Otoacoustic emissions are due to a wave exiting the cochlea via the oval window, and propagating back through the middle ear to the eardrum, and out the ear canal, where it can be picked up by a microphone. Otoacoustic emissions
Evolution of the cochlea apex of the cochlea faces more inferiorly in the hominins than the latter two groups. Finally, the cochlea of European middle Pleistocene hominins faces more inferiorly than Neanderthals, modern humans, and Homo erectus. Human beings, along with Apes, are the only mammals that do not have high frequency (>32 kHz) hearing. Humans have long cochleae, but the space devoted to each frequency range is quite large (2.5mm per octave), resulting in a comparatively reduced upper frequency limit. The human cochlea has approximately 2.5 turns around the modiolus (the axis). Humans, like many mammals and birds, are able to perceive auditory