Cognitive factors contribute to speech perception in cochlear-implant users and age-matched normal-hearing listeners under vocoded conditions.

Erin R O'Neill,Andrew J Oxenham,Heather A Kreft

doi:10.1121/1.5116009

Erin R O'Neill, Andrew J Oxenham + Show 1 more

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https://doi.org/10.1121/1.5116009

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Abstract

This study examined the contribution of perceptual and cognitive factors to speech-perception abilities in cochlear-implant (CI) users. Thirty CI users were tested on word intelligibility in sentences with and without semantic context, presented in quiet and in noise. Performance was compared with measures of spectral-ripple detection and discrimination, thought to reflect peripheral processing, as well as with cognitive measures of working memory and non-verbal intelligence. Thirty age-matched and thirty younger normal-hearing (NH) adults also participated, listening via tone-excited vocoders, adjusted to produce mean performance for speech in noise comparable to that of the CI group. Results suggest that CI users may rely more heavily on semantic context than younger or older NH listeners, and that non-auditory working memory explains significant variance in the CI and age-matched NH groups. Between-subject variability in spectral-ripple detection thresholds was similar across groups, despite the spectral resolution for all NH listeners being limited by the same vocoder, whereas speech perception scores were more variable between CI users than between NH listeners. The results highlight the potential importance of central factors in explaining individual differences in CI users and question the extent to which standard measures of spectral resolution in CIs reflect purely peripheral processing.

Highlights

The limited number of electrodes and the effects of electrical field spread, due to the distance between the electrode and the spiral ganglion cells, lead to limited spectral resolution in CIs
One striking finding from this study was the large decrement in speech intelligibility found for CI users when semantic context was not available
Whereas the difference in performance of the age-matched and young NH listeners between context and nonsense sentences was about 15 percentage points on average, the difference for the CI users was about 30 percentage points. This difference was observed despite the fact that performance in the context sentences was very similar across all three listener groups, due to the use of a vocoder with the NH groups. One interpretation of this finding is that CI users have learned through experience to make more use of semantic context information than NH listeners, due perhaps to the fact that the CI users are continually presented with degraded auditory input

Summary

Introduction

The limited number of electrodes and the effects of electrical field spread, due to the distance between the electrode and the spiral ganglion cells, lead to limited spectral resolution in CIs. Some studies in CI users have found a correlation between measures of spectral resolution (e.g., spectral-ripple discrimination or spatial tuning curves) and speech perception in quiet (Anderson et al, 2011; Henry and Turner, 2003; Henry et al, 2005) and in noise (Gifford et al, 2018; Won et al, 2007), others have not (Anderson et al, 2012).

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