[Is the duplicity theory of the hair cells still valid today?].

The "Duplizitätstheorie" of Meyer zum Gottesberge (1948) states that signal processing takes place at low sound intensities on the nerve fibers of the outer hair cells, whereas at high sound intensities on the nerve fibers of the inner hair cells. The discovery of oto-acoustic emissions by Kemp (1978) makes a modification of the "Duplizitätstheorie" necessary. The outer hair cells are supposed to be motor-drives final control elements to enhance the sensitivity of inner hair cells. Thus outer hair cells do not serve for the direct transmission of information in the sense of neural coding. Signal processing takes place at all intensities exclusively on the nerve fibers of the inner hair cells.