Modeling normal and impaired hearing: implications for hearing aid design.

A cochlear simulation has been developed to model normal and impaired hearing. The simulation includes the middle ear, the mechanical motion of the cochlear partition, and the mechanical to neural transduction of the inner hair cells. The outer hair cells are postulated to provide an active feedback mechanism that adjusts the gain and shape of the auditory filters. Auditory impairment is simulated by reducing the efficacy of the outer hair cells and by modifying the inner hair cell transduction process. The effects of simulated impairment are illustrated for two speech sounds, /ba/ and /ka/, with the neural firing patterns from the impaired ear compared with those of a normal ear. The differences in the neural firing patterns are interpreted in the context of hearing aid signal processing.