Project Abstract/Summary The mammalian cochlea achieves its outstanding performance characteristics by including a physiologically vul- nerable active process that strategically amplifies waves as they propagate through the cochlear spiral. As a result of this spatially coordinated and nonlinear wave amplification, the cochlear response at one characteristic- frequency location largely depends upon the physiological status and the response in more basal regions. In response to complex sounds, waves of different frequency nonlinearly interact along the cochlea, mutually sup- pressing one with the other. In contrast to a bank of independently operating filters commonly used to depict cochlear function, the responses of distinct “cochlear filters" are strongly coupled by nonlinear wave interactions. Although nonlinear wave interactions play a major role for the cochlea response, their role for encoding complex sounds in the auditory periphery—and consequently their contribution to central auditory mechanisms—is poorly understood and largely ignored. Understanding nonlinear wave interactions is hence essential to establish how the cochlea encodes eco- logically relevant sounds and the role of the auditory periphery for sound perception. Because nonlinear wave interactions depend upon the health of the ear, understanding these interactions is fundamental also to establish how cochlear impairment affects the peripheral representation of complex sounds. Further, because even mild sensorineural hearing loss greatly degrades behavioral performance in acoustically challenging situations, it is likely that nonlinear wave interactions underlie unexplored mechanisms for the outstanding performance of the healthy ear. My project will tackle these issues by: (i) deriving from the experimental data a cochlear model that reproduces accurately nonlinear wave interactions in laboratory animals (Aim 1.a) and humans (Aim 1.b); (ii) testing the hypothesis that nonlinear wave interactions underly beneficial mechanisms to encode sounds in acoustically adverse situations (Aim 2.a), and (iii) determining how and with what limitations the effects of nonlinear wave interactions elucidated in this project are accounted for by popular computer models of the auditory periphery (Aim 2.b). The results of this project will not only challenge and improve the current understanding of cochlear function for hearing, but will also find natural application in improving models of hearing impairment, and in determining novel cochlear-inspired strategies to improve the performance of assistive hearing technology.