Resonant modes and musical ratios in otoacoustic emissions.

The ratios between frequency components of evoked otoacoustic emissions (OAE) were investigated for 100 ears. The signals were decomposed by means of an adaptive approximation method into basic waveforms coming from a very large and redundant dictionary of Gabor functions. The high time-frequency resolution of the method and the parametric representation of the waveforms allowed for an estimation of the frequency ratios of the basic components. A repetitive occurrence of the "fifths", "fourths" and octaves connected with the Pythagorean temperament was found. The octaves containing "fifths" were identified. This kind of sequences in OAE tend to appear in the same form for tonal stimulations of different frequencies and for broadband stimuli. The significance of the results was confirmed by comparison to Monte Carlo simulations of the null hypothesis of random distribution of frequency modes. These findings support the resonance theory of hearing, which binds musical ratios with the geometrical spacing of outer hair cells in the cochlea.