Cochlear nonlinearity: Implications for auditory signal processing and perception

Conscious perception of auditory nonlinearity in combination tones, the low-frequency intermodulation products of two or more tones, goes at least back to Tartini (1692–1770). Renewed interest around 1970 [e.g., J. L. Goldstein, J. Acoust. Soc. Am. 41, 676–689 (1967); J. L. Hall, J. Acoust. Soc. Am. 56, 1818–1828 (1974); G. F. Smoorenburg, J. Acoust. Soc. Am. 52, 615–632 (1972)] led to the conclusion that the nonlinearity originates in the (intact) cochlea. At that time, nobody paid special attention to the point that acoustical effects within the cochlea should be reflected at the aural entrance. Today, that issue (DPOAE) is actively explored. The link with auditory perception receives lesser emphasis, hopefully not because a proper psychoacoustic measurement requires more than reading a stimulus parameter (cf. Psychoacoustics and David M. Green). Next, two-tone suppression became an issue where psychological and physiological nonlinear acoustics met. The phenomena are intertwined, and probably inseparable from the point of view of underlying biophysical mechanism. Finally, obviously the auditory nonlinearity is compressive. The negligible impact of this result on development of a biophysical basis for the auditory dynamic range and the decibel scale remains puzzling.