Effect of frequency mismatch and band partitioning on vocal tract length perception in vocoder simulations of cochlear implant processing.

Nawal El Boghdady,Etienne Gaudrain,Deniz Başkent

doi:10.1121/1.5041261

Nawal El Boghdady, Etienne Gaudrain + Show 1 more

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https://doi.org/10.1121/1.5041261

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Abstract

The vocal tract length (VTL) of a speaker is an important voice cue that aids speech intelligibility in multi-talker situations. However, cochlear implant (CI) users demonstrate poor VTL sensitivity. This may be partially caused by the mismatch between frequencies received by the implant and those corresponding to places of stimulation along the cochlea. This mismatch can distort formant spacing, where VTL cues are encoded. In this study, the effects of frequency mismatch and band partitioning on VTL sensitivity were investigated in normal hearing listeners with vocoder simulations of CI processing. The hypotheses were that VTL sensitivity may be reduced by increased frequency mismatch and insufficient spectral resolution in how the frequency range is partitioned, specifically where formants lie. Moreover, optimal band partitioning might mitigate the detrimental effects of frequency mismatch on VTL sensitivity. Results showed that VTL sensitivity decreased with increased frequency mismatch and reduced spectral resolution near the low frequencies of the band partitioning map. Band partitioning was independent of mismatch, indicating that if a given partitioning is suboptimal, a better partitioning might improve VTL sensitivity despite the degree of mismatch. These findings suggest that customizing the frequency partitioning map may enhance VTL perception in individual CI users.

Highlights

In individuals with profound sensorineural hearing loss, functional hearing can be restored with the help of a multichannel cochlear implant (CI): a neural prosthetic device that electrically stimulates the auditory nerve fibres
CI users exhibit poor perception of vocal cues, especially vocal tract length (VTL), which may be a result of two effects
The first is the frequency mismatch between the frequencies received by the implant and those corresponding to the actual place of stimulation in the cochlea

Summary

Introduction

In individuals with profound sensorineural hearing loss, functional hearing can be restored with the help of a multichannel cochlear implant (CI): a neural prosthetic device that electrically stimulates the auditory nerve fibres. Normal hearing (NH) listeners can understand speech relatively well in such situations, which has been shown to be linked, in part, to the voice differences between target and masking speakers (e.g., Brungart, 2001; Festen and Plomp, 1990; Stickney et al, 2004). In those studies, target recognition a)Portions of this work were presented in “Effect of frequency allocation on vocal tract length perception in cochlear implant users,” Conference on Implantable Auditory Prostheses (CIAP’ 15). No release from masking for CI users was observed when either F0 (Pyschny et al, 2011; Stickney et al, 2007), VTL (Pyschny et al, 2011), or both (Pyschny et al, 2011) were varied between target and masking speakers, or when completely

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