On mechanical preprocessing in the cochlea: the three great hearing theories combined.

Since otoacoustic emissions were discovered, the old idea of a second (active) filter in the cochlea has been pursued with considerable dedication. In this contribution a concept explaining the action of the second filter is presented, which is derived from high-frequency resonance: The outer hair cells are excited when the traveling wave breaks rather than when it reaches its peak amplitude. They vibrate at a much higher frequency, i.e. their mechano-electrical resonant frequency. The amplitude of the exciting stimulus is very small, but in keeping with the chaos theory it is amplified by self-organization to a level sufficient for physiologic excitation. This concept helps to explain the hitherto unexplained frequency changes of spontaneous otoacoustic emissions.