The in ̄uence of stochastic behavior on the human threshold of hearing

The inner hair cells in the cochlea perform the crucial task of transforming mechanical sound signals into electrical activity. The cochlear nerve ®bers code this information and convey it to the brain for further processing. This study investigates the performance of the system inner hair cell ± primary auditory a€erent nerve ®bers at the physical limit of the mechano-electrical transduction for the human auditory frequency range. The Brownian motion of the hair cellÕs receptive organelle, the hair bundle, does not blunt the sensitivity, but in fact enlarges ± especially in frequency regions which are most important for the perception of music and speech ± via the mechanism of nonlinear stochastic resonance (SR) the dynamical range of the mechano-electrical transduction by at least one order of magnitude. The coding eciency of small sinusoidal hair bundle de ̄ections shows basic properties of the human hearing threshold curve for pure tones and corresponds to experimental results of noise-induced tuning curves in mechano-receptors in the rat foot. Furthermore, the model explains how altered coding eciency contributes to pathological changes in the spiking pattern which arise from morphological changes in the hair bundle structure (e.g., in noise-induced sensorineural hearing loss of cochlear origin). Ó 2000 Elsevier Science Ltd. All rights reserved.