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Effects of tonotopic matching and spatial cues on segregation of competing speech in simulations of bilateral cochlear implants

In the clinical fitting of cochlear implants (CIs), the lowest input acoustic frequency is typically much lower than the characteristic frequency associated with the most apical electrode position, due to the limited electrode insertion depth. For bilateral CI users, electrode positions may differ a...

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Autores principales: Thomas, Mathew, Willis, Shelby, Galvin, John J., Fu, Qian-Jie
Formato: Online Artículo Texto
Lenguaje:English
Publicado: Public Library of Science 2022
Materias:
Acceso en línea:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9255761/
https://www.ncbi.nlm.nih.gov/pubmed/35788202
http://dx.doi.org/10.1371/journal.pone.0270759
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author Thomas, Mathew
Willis, Shelby
Galvin, John J.
Fu, Qian-Jie
author_facet Thomas, Mathew
Willis, Shelby
Galvin, John J.
Fu, Qian-Jie
author_sort Thomas, Mathew
collection PubMed
description In the clinical fitting of cochlear implants (CIs), the lowest input acoustic frequency is typically much lower than the characteristic frequency associated with the most apical electrode position, due to the limited electrode insertion depth. For bilateral CI users, electrode positions may differ across ears. However, the same acoustic-to-electrode frequency allocation table (FAT) is typically assigned to both ears. As such, bilateral CI users may experience both intra-aural frequency mismatch within each ear and inter-aural mismatch across ears. This inter-aural mismatch may limit the ability of bilateral CI users to take advantage of spatial cues when attempting to segregate competing speech. Adjusting the FAT to tonotopically match the electrode position in each ear (i.e., increasing the low acoustic input frequency) is theorized to reduce this inter-aural mismatch. Unfortunately, this approach may also introduce the loss of acoustic information below the modified input acoustic frequency. The present study explored the trade-off between reduced inter-aural frequency mismatch and low-frequency information loss for segregation of competing speech. Normal-hearing participants were tested while listening to acoustic simulations of bilateral CIs. Speech reception thresholds (SRTs) were measured for target sentences produced by a male talker in the presence of two different male talkers. Masker speech was either co-located with or spatially separated from the target speech. The bilateral CI simulations were produced by 16-channel sinewave vocoders; the simulated insertion depth was fixed in one ear and varied in the other ear, resulting in an inter-aural mismatch of 0, 2, or 6 mm in terms of cochlear place. Two FAT conditions were compared: 1) clinical (200–8000 Hz in both ears), or 2) matched to the simulated insertion depth in each ear. Results showed that SRTs were significantly lower with the matched than with the clinical FAT, regardless of the insertion depth or spatial configuration of the masker speech. The largest improvement in SRTs with the matched FAT was observed when the inter-aural mismatch was largest (6 mm). These results suggest that minimizing inter-aural mismatch with tonotopically matched FATs may benefit bilateral CI users’ ability to segregate competing speech despite substantial low-frequency information loss in ears with shallow insertion depths.
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spelling pubmed-92557612022-07-06 Effects of tonotopic matching and spatial cues on segregation of competing speech in simulations of bilateral cochlear implants Thomas, Mathew Willis, Shelby Galvin, John J. Fu, Qian-Jie PLoS One Research Article In the clinical fitting of cochlear implants (CIs), the lowest input acoustic frequency is typically much lower than the characteristic frequency associated with the most apical electrode position, due to the limited electrode insertion depth. For bilateral CI users, electrode positions may differ across ears. However, the same acoustic-to-electrode frequency allocation table (FAT) is typically assigned to both ears. As such, bilateral CI users may experience both intra-aural frequency mismatch within each ear and inter-aural mismatch across ears. This inter-aural mismatch may limit the ability of bilateral CI users to take advantage of spatial cues when attempting to segregate competing speech. Adjusting the FAT to tonotopically match the electrode position in each ear (i.e., increasing the low acoustic input frequency) is theorized to reduce this inter-aural mismatch. Unfortunately, this approach may also introduce the loss of acoustic information below the modified input acoustic frequency. The present study explored the trade-off between reduced inter-aural frequency mismatch and low-frequency information loss for segregation of competing speech. Normal-hearing participants were tested while listening to acoustic simulations of bilateral CIs. Speech reception thresholds (SRTs) were measured for target sentences produced by a male talker in the presence of two different male talkers. Masker speech was either co-located with or spatially separated from the target speech. The bilateral CI simulations were produced by 16-channel sinewave vocoders; the simulated insertion depth was fixed in one ear and varied in the other ear, resulting in an inter-aural mismatch of 0, 2, or 6 mm in terms of cochlear place. Two FAT conditions were compared: 1) clinical (200–8000 Hz in both ears), or 2) matched to the simulated insertion depth in each ear. Results showed that SRTs were significantly lower with the matched than with the clinical FAT, regardless of the insertion depth or spatial configuration of the masker speech. The largest improvement in SRTs with the matched FAT was observed when the inter-aural mismatch was largest (6 mm). These results suggest that minimizing inter-aural mismatch with tonotopically matched FATs may benefit bilateral CI users’ ability to segregate competing speech despite substantial low-frequency information loss in ears with shallow insertion depths. Public Library of Science 2022-07-05 /pmc/articles/PMC9255761/ /pubmed/35788202 http://dx.doi.org/10.1371/journal.pone.0270759 Text en © 2022 Thomas et al https://creativecommons.org/licenses/by/4.0/This is an open access article distributed under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0/) , which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
spellingShingle Research Article
Thomas, Mathew
Willis, Shelby
Galvin, John J.
Fu, Qian-Jie
Effects of tonotopic matching and spatial cues on segregation of competing speech in simulations of bilateral cochlear implants
title Effects of tonotopic matching and spatial cues on segregation of competing speech in simulations of bilateral cochlear implants
title_full Effects of tonotopic matching and spatial cues on segregation of competing speech in simulations of bilateral cochlear implants
title_fullStr Effects of tonotopic matching and spatial cues on segregation of competing speech in simulations of bilateral cochlear implants
title_full_unstemmed Effects of tonotopic matching and spatial cues on segregation of competing speech in simulations of bilateral cochlear implants
title_short Effects of tonotopic matching and spatial cues on segregation of competing speech in simulations of bilateral cochlear implants
title_sort effects of tonotopic matching and spatial cues on segregation of competing speech in simulations of bilateral cochlear implants
topic Research Article
url https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9255761/
https://www.ncbi.nlm.nih.gov/pubmed/35788202
http://dx.doi.org/10.1371/journal.pone.0270759
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