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 signals that displace the eardrum by a mere picometre. Because of its prominence and preserved state in the fossil record, until recently, the ear had been used to determine phylogeny. The ear itself contains different portions, including the outer ear, the middle ear, and the inner ear and all of these show evolutionary changes that are often unique to each lineage [14]. It was the independent evolution of a tympanic middle ear in the Triassic era that produced strong selection pressures towards improved hearing organs in the separate lineages of land vertebrates. The cochlea is the tri-chambered auditory detection portion