Behavioural and Electrophysiological Measures of Electrode Discriminaiton in Adult Auditory Brainstem Implant users

Abstract

Auditory brainstem implants ABI are a recognised form of treatment in cases of neural hearing loss where amplification with conventional hearing aids or with cochlear implants (CI) is not beneficial. Using an electrode array surgically positioned in or on the ventral cochlear nucleus (VCN) in the brainstem, an ABI can stimulate neural pathways central to any damage so that auditory sensation may still be achieved. Outcomes are varied with an ABI and often poorer than those of CI users. A large part of ABI programming involves the evaluation of pitch variations between electrodes, and the benefit of spectral distinction is considered to be a benefit of multichannel implants. However, the auditory perceptual differences between ABI electrodes vary. This study therefore aimed to investigate place-pitch perception and judgements of non-tonotopic auditory perceptual differences between electrodes via both subjective and objective measures. For ABI users, understanding more about the auditory perceptual differences between electrodes may have clinical benefits during programming sessions.Experiment one used psychophysical measures to investigate place-pitch perception and auditory perceptual differences between electrodes in ABI users, given that tonotopic ordering of electrodes is an overriding part of programming sessions and has been cited to have an effect on outcomes. Experiment one (Chapter 3) therefore had two aims: (a) to determine the relationship between place-pitch perception and speech outcomes in ABI users using their clinically-set maps; (b) to determine if auditory percepts other than pitch are related to electrode position for ABI users via a multidimensional scaling (MDS) procedure. Ten CI and 9 ABI users participated in experiment 1. CI and ABI speech perception scores were correlated with tonotopically accurate user maps and with more distinguishable pitch variations between electrodes. MDS analysis revealed that auditory percepts experienced via an ABI are different to those of a CI and that pitch perception is not likely to be the overriding auditory percept for an ABI user.Experiment two used electrically-evoked event-related potentials (EERPs) to investigate auditory perceptual differences between implant electrodes. Experiment two (Chapter 4) therefore had two aims: a) to determine if electrophysiological measures of electrode discrimination correlate with behavioural measures of electrode discrimination in adult ABI users; b) to determine if electrically-evoked ERPs correlate with clinically recorded speech scores in adult ABI users. N1, P2, MMN, P3a and P3b were elicited in ABI users. Difficulty in controlling for variations in auditory perception meant a wide range of ERP latencies were identified. The variations meant there were insufficient data to accurately test the hypothesis that P3b and MMN latency increases with increasing task difficulty in ABI users. A significant negative correlation was found with mean MMN latency and word and sentence scores in CI users and with P3a amplitude and word scores in ABI users. A significant relationship was also found between MMN latencies and behavioural measures of pitch discrimination between electrodes, providing some support for the hypothesis that electrophysiological measures of electrode discrimination may be related to behavioural measures of electrode discrimination.This study has shown that electrophysiological measures of electrode discrimination are recordable in ABI users, but the relative uncertainty regarding the degree of perceptual difference to which they are elicited may limit their efficacy.

Date of Award	31 Dec 2013
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Wael El-Deredy (Supervisor) & Colette Mckay (Supervisor)