Short-term adaptation in acoustical and cochlear-implant hearing

Abstract

Sound onset and changes in sound intensity appear to play important roles in many aspects of hearing, e.g., detection, speech communication, and source identification. Perhaps for this reason the auditory system displays mechanisms that emphasize changes in sound intensity at multiple levels of neurophysiological processing. Short-term adaptation, observed in auditory-nerve responses, is perhaps the most peripheral example of onset emphasis. It can be observed in its simplest form in the auditory-nerve response to a constant-intensity tone burst where firing rate is maximum at response onset and decays to a steady-state value during the tone. Firing rate drops below spontaneous rate following tone offset, and the response to brief probe tones is reduced and gradually recovers in this post-stimulation interval. Short-term adaptation is generally assumed to occur in auditory hair cells and cochlear-implant stimulation by-passes hair cells and hence this potential source of adaptation. The results reviewed here will describe a model of peripheral short-term adaptation and how this model can be added to cochlear-implant speech processing. Preliminary results will be presented that indicate that adding short-term adaptation to cochlear-implant processing produces an improvement in speech intelligibility on the order of 5% to 10% in a variety of listening tasks.