Saleh, SMI; (2013) The Efficacy of Fitting Cochlear Implants Based on Pitch Perception. Doctoral thesis , UCL (University College London).

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Abstract

Cochlear implants (CI) provide useful hearing for many hearing-impaired individuals. The CI’s external sound processor has to be programmed to optimise performance. However, performance varies greatly amongst CI recipients. This thesis evaluated a pure-tone electrode-differentiation (PTED) pitch-ranking task for optimising programming. The PTED was evaluated for reliability, validity and clinical-suitability. PTED scores were a significant (p<0.05) predictor of speech-perception. The angular-depth-of-insertion for the CI array was estimated for 16 recipients, there was a significant correlation with speech-perception. Cone beam computed tomography (CBCT) increased accuracy for estimating scalar-placement of electrodes and no association was found with speech-perception. 25 unilaterally-implanted recipients received programs with indiscriminable electrodes deactivated based on PTED. Two programs were provided, one with the same rate-of-pulses-per-channel (RPC) as the clinical program and one with increased RPC. Programs were evaluated in a cross-over study. Speech-perception was evaluated using BKB (Bamford-Kowal-Bench) sentences in quiet and noise and the Coordinate Response Measure (CRM). Statistically significant improvements were found with at least one research program on all measures. A pure-tone intermediate frequency (PTIF) task was conducted to compare pitch perception in regions of good ED with regions of poor ED. Participants gaining benefit from electrode deactivation had fewer intermediate frequencies (IF) in poor ED regions compared to good ED regions and more IF in electrode deactivation regions following deactivation. This pattern was not observed in participants not gaining benefit from electrode deactivation. Six bilaterally-implanted participants underwent pitch matching between ears and new programs were created using only discriminable electrodes. Two matching approaches were used; direct stimulation via clinical equipment and pure-tone stimulation. Significant improvements were found in localisation and BKB in noise with at least one research program. The results of these experiments suggest potential for improving performance for CI users by programming based on PTED; a clinically viable task.

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