A Model for the representation of Speech Signals in Normal and Impaired Ears

A model of human auditory periphery, ranging from the outer ear to the auditory nerve, was developed. The model consists of the following components: outer ear transfer function, middle ear transfer function, basilar membrane velocity, inner hair cell receptor potential, inner hair cell probability of neurotransmitter release and auditory nerve fibre refractoriness. The model builds on previously published models, however, parameters for basilar membrane velocity and inner hair cell probability of neurotransmitter release were successfully fitted to model data from psychophysical and physiological data for normal hearing and impaired hearing. The psychophysical data consisted in forward masking data from three studies. The “temporal window model” was tested and found to account for the data, except for low frequency stimulus. It was suggested that the temporal window should be frequency dependent. Impaired hearing was modelled as a combination of outer- and inner hair cell loss. The percentage of dead inner hair cells was calculated based on a new computational method relating auditory nerve fibre thresholds to behavioural thresholds. Finally, a model of the entire auditory nerve fibre population was proposed for normal and impaired hearing.