THE ROLE OF FREQUENCY, TIMING AND LEVEL DISTORTION ON BINAURAL PROCESSING IN SIMULATIONS OF COCHLEAR IMPLANT USERS WITH SINGLE-SIDED DEAFNESS

Abstract

Cochlear implants are a promising new treatment option for single-sided deafness. Cochlear implants for single-sided deafness have been shown to improve speech perception in noise and aid in sound localization. However, this intervention is not as good as acoustic hearing and listeners’ exhibit large amounts of variability in hearing outcomes. These limitations may be caused by certain distortions inherent in the processing of the sound signals by the cochlear implant. This dissertation examined the role that three key cochlear implant distortions might play in limiting speech perception in noise for listeners with single-sided deafness. The first distortion examined was the frequency mismatch between the cochlear implant and the acoustic ear. The next distortion examined was the effect of timing differences between the cochlear implant and the normal hearing ear. Finally, the effect of compression on hearing speech in spatial noise was investigated. These limitations and distortions could limit binaural processing ability in those with single-sided deafness who receive a cochlear implant. The goal of this dissertation was to examine the role of cochlear-implant distortions on binaural hearing using simulations of cochlear implant processing presented to normal-hearing listeners. Normal-hearing listeners were presented with vocoder simulations of cochlear-implant processing to one ear, and unprocessed signals to the other ear. These simulations were used to examine the ability to understand binaural speech signals in noisy environments and to examine auditory object formation in simulated free-field environments. These data provided insight into how CI distortions and mapping strategies can limit binaural benefits for those with single-sided deafness. Knowledge of these limitations could lead to better programming strategies to improve binaural hearing and quality of life for those with single-sided deafness who receive a cochlear implant.