Cochlear Model for Hearing Loss

In many psychoacoustical tasks, hearing-impaired subjects display abnormal audiograms and poor understanding of speech compared to normal listeners. Existing models that ex‐ plain the performance of the hearing impaired indicate that possible sources for cochlear hearing loss may be the dysfunction of the outer and inner hair cells. In this study, a model of the auditory system is introduced. It includes two stages: (1) a nonlinear time domain cochlear model with active outer hair cells that are driven by the tectorial mem‐ brane motion and (2) a synaptic model that generates the auditory nerve instantaneous rate as a response to the basilar membrane motion and is affected by the inner hair cell transduction efficiency. The model can fit both a normal auditory system and an abnor‐ mal auditory system with easily induced pathologies. In typical psychoacoustical detection experiments, the ability of subjects to perceive a minimum difference in a physical property is measured. We use the model presented here to predict these performances by assuming that the brain behaves as an optimal pro‐ cessor that estimates a particular physical parameter. The performance of the optimal processor is derived by calculating its lower bound. Since neural activity is described as a nonhomogeneous Poisson process whose instantaneous rate was derived, the Cramer– Rao lower bound can be analytically obtained for both rate coding and all information coding. We compared the model predictions of normal and abnormal cochleae to human thresh‐ olds of pure tones in quiet and in the presence of background noise.