title: Distortion products and backward-traveling waves in nonlinear active models of the cochlea.
abstract: This study explores the phenomenology of distortion products in nonlinear cochlear models, predicting their amplitude and phase along the basilar membrane. The existence of a backward-traveling wave at the distortion-product frequency, which has been recently questioned by experiments measuring the phase of basilar-membrane vibration, is discussed. The effect of different modeling choices is analyzed, including feed-forward asymmetry, micromechanical roughness, and breaking of scaling symmetry. The experimentally observed negative slope of basilar-membrane phase is predicted by numerical simulations of nonlinear cochlear models under a wide range of parameters and modeling choices. In active models, positive phase slopes are predicted by the quasi-linear analytical computations and by the fully nonlinear numerical simulations only if the distortion-product sources are localized apical to the observation point and if the stapes reflectivity is unrealistically small. The results of this study predict a negative phase slope whenever the source is distributed over a reasonably wide cochlear region and/or a reasonably high stapes reflectivity is assumed. Therefore, the above-mentioned experiments do not contradict "classical" models of cochlear mechanics and of distortion-product generation.
authors.affiliation: Dipartimento Igiene del Lavoro, INAIL, Via Fontana Candida 1, 00040 Monte Porzio Catone, Rome, Italy.
authors.forename: Renata
authors.initials: R
authors.lastname: Sisto
authors.forename: Arturo
authors.initials: A
authors.lastname: Moleti
authors.forename: Teresa
authors.initials: T
authors.lastname: Botti
authors.forename: Daniele
authors.initials: D
authors.lastname: Bertaccini
authors.forename: Christopher A
authors.initials: CA
authors.lastname: Shera
mesh_terms: D000162:Acoustics; D003051:Cochlea / Q000502:physiology*; D003198:Computer Simulation; D006801:Humans; D008433:Mathematics; D008959:Models, Neurological; D017711:Nonlinear Dynamics; D017084:Otoacoustic Emissions, Spontaneous / Q000502:physiology; D010469:Perceptual Distortion / Q000502:physiology*; D013199:Stapes / Q000502:physiology; D014732:Vibration