Spectral Processing In Cochlear Implants

Cochlear implants are now an accepted clinical device for the alleviation of severe to profound deafness. Currently more than 60,000 people are users of cochlear implants, and this number is increasing rapidly as the technology improves and criteria for candidacy widen. A multiple-electrode cochlear implant directly stimulates the remaining peripheral auditory nerve (AN) cells within the spiral ganglion of the cochlea with current delivered by an array of electrodes inserted into the scala tympani of the cochlea. As such, the array of electrodes is designed to at least partially restore the function of the cochlea as an important organ for spectral processing (see Chapter 1 by Lopez-Poveda). Because the peripheral processing of the normal external, middle, and inner ear is bypassed by a cochlear implant, it is possible to produce peripheral neural activation patterns that are different from those produced by normal hearing. Thus, cochlear implant research has the potential to provide additional insight into the normal central auditory processing of spectral information. It should be remembered, however, that severe peripheral hearing loss can be accompanied by plastic changes throughout the central auditory system (Hardie and Shepherd, 1999; Shepherd and Hardie, 2001). Therefore, the results of cochlear implant research can be applied only in a qualified way to the understanding of normal processes. On the other hand, examining how people learn to listen with a cochlear implant can provide insight into how the central auditory system responds to new patterns of stimulation. In the following sections, a brief summary of a how a cochlear implant works is first presented. In later sections, the perception of spectral and temporal information in simple and more complex stimuli is discussed. Finally, the plasticity of the central auditory system in adapting to electrical stimulation is discussed. © 2005 Elsevier Inc. All rights reserved.