A Dynamically Focusing Cochlear Implant Strategy Can Improve Vowel Identification in Noise

Objectives: The standard, monopolar (MP) electrode configuration used in commercially available cochlear implants (CI) creates a broad electrical field, which can lead to unwanted channel interactions. Use of more focused configurations, such as tripolar and phased array, has led to mixed results for improving speech understanding. The purpose of the present study was to assess the efficacy of a physiologically inspired configuration called dynamic focusing, using focused tripolar stimulation at low levels and less focused stimulation at high levels. Dynamic focusing may better mimic cochlear excitation patterns in normal acoustic hearing, while reducing the current levels necessary to achieve sufficient loudness at high levels. Design: Twenty postlingually deafened adult CI users participated in the study. Speech perception was assessed in quiet and in a four-talker babble background noise. Speech stimuli were closed-set spondees in noise, and medial vowels at 50 and 60 dB SPL in quiet and in noise. The signal to noise ratio was adjusted individually such that performance was between 40 and 60% correct with the MP strategy. Subjects were fitted with three experimental strategies matched for pulse duration, pulse rate, filter settings, and loudness on a channel-by-channel basis. The strategies included 14 channels programmed in MP, fixed partial tripolar (σ = 0.8), and dynamic partial tripolar (σ at 0.8 at threshold and 0.5 at the most comfortable level). Fifteen minutes of listening experience was provided with each strategy before testing. Sound quality ratings were also obtained. Results: Speech perception performance for vowel identification in quiet at 50 and 60 dB SPL and for spondees in noise was similar for the three tested strategies. However, performance on vowel identification in noise was significantly better for listeners using the dynamic focusing strategy. Sound quality ratings were similar for the three strategies. Some subjects obtained more benefit than others, with some individual differences explained by the relation between loudness growth and the rate of change from focused to broader stimulation. Conclusions: These initial results suggest that further exploration of dynamic focusing is warranted. Specifically, optimizing such strategies on an individual basis may lead to improvements in speech perception for more adult listeners and improve how CIs are tailored. Some listeners may also need a longer period of time to acclimate to a new program. This is an open-access article distributed under the terms of the Creative Commons Attribution-Non Commercial-No Derivatives License 4.0 (CCBY-NC-ND), where it is permissible to download and share the work provided it is properly cited. The work cannot be changed in any way or used commercially without permission from the journal. Supplemental digital content is available for this article. Direct URL citations appear in the printed text and are provided in the HTML and text of this article on the journal's Web site (www.ear-hearing.com). ACKNOWLEDGMENTS: The authors thank the cochlear implant subjects who patiently participated in this study. The authors also thank Lindsay DeVries and Gabrielle O'Brien for assistance with statistical analyses. This work was funded by the National Institutes of Health, National Institute of Deafness and Other Communication Disorders R01DC012142 (J.G.A./J.A.B.) and R01DC012262 (A.J.O.). The authors declare no conflicts of interest. Address for correspondence: Julie G. Arenberg, Department of Speech and Hearing Sciences, University of Washington, 1417 NE 42nd Street, Box 354875, Seattle, WA 98105, USA. E-mail: jbierer@uw.edu Received March 24, 2017; accepted January 26, 2018. Copyright © 2018 Wolters Kluwer Health, Inc. All rights reserved.

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