Auditory Perception and the Electrode-Neuron Interface in Children and Adults with Cochlear Implants

Abstract

Cochlear implants (CIs) restore auditory perception to individuals with severe to profound hearing loss, yet identification of speech sounds remains limited due to degraded or distorted representations of frequency information. Spectral resolution, the ability to resolve the frequency components of an auditory signal, is essential for accurate speech identification but is limited in CI users of all ages. Spectral resolution of individuals with CIs can be further impaired by suboptimal interfaces between CI electrodes and auditory neurons in the cochlea. These interfaces could result from neuronal degeneration that occurred during the period of deafness prior to implantation, CI electrodes located distant to auditory neurons, or bone and tissue growth in the cochlea after CI surgery. The aim of this dissertation was to investigate the relation between the electrode-neuron interface and auditory perception in children and adults with CIs. These experiments respectively examined 1) the patterns of phoneme identification errors resulting from specific spectral degradations that mimicked the effects of poor electrode-neuron interfaces, 2) the developmental time course of spectral resolution and vowel identification in pediatric CI users, 3) auditory perception related to the electrode-neuron interface in two groups with divergent hearing histories: early-implanted children and late-implanted adults, and 4) speech-based spectral resolution in children and adults with normal hearing and with CIs. The results from these experiments provide an improved understanding of the effects of suboptimal CI electrode-neuron interfaces on spectral resolution and phoneme identification performance of CI users. Findings from these studies also indicated that cochlear implantation in children enhances auditory system development and drives maturation of auditory perception. Finally, these experiments demonstrated that prelingually-deafened, early-implanted children differ from postlingually-deafened, later implanted adults in both cochlear physiology and integration of acoustic cues for speech sounds. The knowledge gained from this dissertation laid the foundation for the creation of experimental CI program processing strategies to enhance spectral transmission for children and adults with CIs.