Using Binaural Beat Sensitivity To Describe Mechanisms That May Enhance Binaural Interactions In Single-Sided-Deafness Cochlear-Implant Patients

Abstract

Patients with single-sided deafness (SSD) have difficulty localizing sound and understanding speech in noisy backgrounds. Currently, if treated at all, SSD patients may be fitted with devices that route sounds from the deaf side to the better ear. These devices have two primary limitations: (1) they decrease the signal-to-noise ratio when target signals originate on the side with the normal-hearing ear, and (2) they do not restore spatial hearing (e.g., Kitterick, Smith, & Lucas, 2016). Recently, some SSD patients have received a cochlear implant (CI) in their deaf ear (SSD+CI). The aim of this thesis was to investigate the outcomes from the intervention, to determine the mechanisms underlying any observed improvements, and to test a novel CI fitting method designed to optimize the interactions between the normal-hearing ear and the CI. Data from the first study indicated that localization and speech understanding may improve after implantation, but the improvements are generally small and are primarily mediated by head-shadow effects. The lack of greater benefits of spatial hearing and spatial release from masking in speech experiments may be due in part to the poor match of spectral location between the two ears. Current fitting strategies attempt to maximize speech perception in the implant alone. However, SSD+CI patients may benefit more from a CI fitting approach that best complements information from the normal-hearing ear by providing a closer match in terms of the tonotopic maps in both ears. The second study explored ways to assess between-ear tonotopic matches using binaural interactions produced by dynamic interaural time differences in the temporal envelope. The final study tested the newly derived maps in terms of their success in improving sound localization and speech in noise perception. Outcomes suggest that frequency-to-place matching alone does not restore binaural integration of the NH and CI ears. Future work should determine whether correcting other mismatches in the time and amplitude-mapping domains, in combination with frequency-to-place matching, will improve speech perception and spatial hearing outcomes.