Otoacoustic emissions (sounds generated by the ear) provide a powerful noninvasive tool for probing the underlying mechanisms of the inner ear. In humans evoked otoacoustic emissions (EOAEs) are currently the only objective means of probing the mechanisms of hearing, and in other mammals the only means for intact ears. Any model claiming to accurately represent the underlying active nonlinear processes associated with hearing must be able to reproduce the rich phenomenology associated with these EOAEs. Spontaneous otoacoustic emissions (SOAES), while apparently playing no direct role in hearing, also have profound implications by their very presence for any realistic model. The current generation of our model of the auditory periphery gives good qualitative agreement with data, but not yet detailed quantitative agreement. We propose a systematic procedure for enhancing our current model to improve the quantitative agreement. In particular, we will incorporate a more realistic model of the underlying linear, active impedance of the organ of Corti. We will also experimentally characterize the variability of the linear, active impedance from the base to the apex, and the form of the cochlear no linearity as well as its variation from the apex to the base. We will incorporate these results into our model. We will develop detailed models of rodent (gerbil, guinea pig, chinchilla) auditory peripheries that will allow us to augment our otoacoustic emission data with published auditory physiological measurements in these species. We will also study theoretically the effects of the surgical modifications on these physiological measurements that will enhance not only our models but will also provide insight into the limitations of these physiological measurements. We will add a model of perception to our model of the auditory periphery and test it by comparing the nonlinear component of otoacoustic emission and psycho acoustic fine structures. This model will allow us to determine which aspects of perceptual no linearity are associated with the auditory periphery and which need to be more centrally located. Furthermore, this model will provide a basis for understanding and modeling the effects of cochlear damage on hearing, and will form the basis for our future plans for studying hearing aid design.
