Mechanism of backward propagation of sound in the cochlea

Cochlea is the auditory sensory organ in the inner ear. It normally transfers sound-induced vibrations of the cochlear partition to bioelectrical signals, which are transmitted to the brain by the auditory nerve. Sensitive cochleae can also generate sounds, named as otoacoustic emissions, which can be measured in the external ear canal. Although otoacoustic emissions have been used to evaluate hearing and to study cochlear mechanism, how emissions exit the cochlea remains unclear. Recent experimental results have showed that the backward delay of emissions is equal to or shorter than the forward delay, indicating that otoacoustic emissions exit the cochlea likely via cochlea fluids as compression waves rather than along the cochlear partition as backward traveling waves.