The frequency analysis of the cochlea – a review of Nobili et al (1998) and Ruggero et al (1992)

Hearing processes seems to divide into three main categories: the caption and transformation of physical sound waves, the transduction of the physical waves into neural patterns and the transformation of these neural patterns into an useful mirror of the physical world. It was thought that the processes of distortion of the physical wave sound, either to enhance the detection of sound origin, either to amplify (or reduce) certain frequencies, was restricted to the pinna (and the head) and middle ear. By the contrary, the inner ear was conceived as a passive transduction mechanism that accurately transduced the physical vibrations produced by the stapes into neural patterns. It is now apparent that the inner ear also interacts with physical waves through a mechanism that is not well known in its details but that seems to involve the motility of the outer hair cells (OHC). This physical capability of the inner ear, besides enhancing frequency discrimination, 1 also explains the existence of otoacoustic emissions, and some auditory illusions (such as the existence of combination tones, or two tone suppressing).