Reverse propagation of sound in the gerbil cochlea.

It is commonly believed that the cochlea emits sounds through backward-traveling waves. In the present experiment using a scanning-laser interferometer, I detected forward-traveling but not backward-traveling waves and found that the stapes vibrates earlier than the basilar membrane. These results contradict the current theory and show that the ear emits sounds through the cochlear fluids as compression waves rather than along the basilar membrane as backward-traveling waves.