Benefits to speech perception in noise from the binaural integration of electric and acoustic signals in simulated unilateral deafness

Ma, Ning; Morris, Saffron D.; Kitterick, P�draig T.

Abstract

Objectives: This study used vocoder simulations with normal-hearing (NH) listeners to (a) measure their ability to integrate speech information from a NH ear and a simulated cochlear implant (CI); and (b) investigate whether binaural integration is disrupted by a mismatch in the delivery of spectral information between the ears arising from a misalignment in the mapping of frequency to place.

Design: Eight NH volunteers participated in the study and listened to sentences embedded in background noise via headphones. Stimuli presented to the left ear were unprocessed. Stimuli presented to the right ear (referred to as the CI-simulation ear) were processed using an 8-channel noise vocoder with one of three processing strategies. An Ideal strategy simulated a frequency-to-place map across all channels that matched the delivery of spectral information between the ears. A Realistic strategy created a misalignment in the mapping of frequency to place in the CI-simulation ear where the size of the mismatch between the ears varied across channels. Finally, a Shifted strategy imposed a similar degree of misalignment in all channels resulting in consistent mismatch between the ears across frequency. The ability to report key words in sentences was assessed under monaural and binaural listening conditions and at signal-to-noise ratios (SNRs) established by estimating speech-reception thresholds in each ear alone. The SNRs ensured that the monaural performance of the left ear never exceeded that of the CI-simulation ear. Binaural integration advantages were calculated by comparing binaural performance with monaural performance using the CI-simulation ear alone. Thus, these advantages reflected the additional use of the experimentally-constrained left ear and were not attributable to better-ear listening.


Results: Binaural performance was as accurate as, or more accurate than, monaural performance with the CI-simulation ear alone. When both ears supported a similar level of monaural performance (50%), binaural integration advantages were found regardless of whether a mismatch was simulated or not. When the CI-simulation ear supported a superior level of monaural performance (71%), evidence of binaural integration was absent when a mismatch was simulated using both the Realistic and Ideal processing strategies. This absence of integration could not be accounted for by ceiling effects or by changes in SNR.

Conclusions: If generalizable to unilaterally-deaf CI users, the results of the current simulation study would suggest that benefits to speech perception in noise can be obtained by integrating information from an implanted ear and a normal-hearing ear. A mismatch in the delivery of spectral information between the ears due to a misalignment in the mapping of frequency to place may disrupt binaural integration in situations where both ears cannot support a similar level of monaural speech understanding. Previous studies which have measured the speech perception of unilaterally-deaf individuals after cochlear implantation but with non-individualized frequency-to-electrode allocations may therefore have underestimated the potential benefits of providing binaural hearing. However, it remains unclear whether the size and nature of the potential incremental benefits from individualized allocations are sufficient to justify the time and resources required to derive them based on cochlear imaging or pitch-matching tasks.

Citation

Ma, N., Morris, S. D., & Kitterick, P. T. (in press). Benefits to speech perception in noise from the binaural integration of electric and acoustic signals in simulated unilateral deafness. Ear and Hearing, 37(3), https://doi.org/10.1097/AUD.0000000000000252

• Journal Article Type: Article
• Acceptance Date: Oct 20, 2015
• Online Publication Date: May 4, 2016
• Deposit Date: Jan 24, 2017
• Publicly Available Date: Jan 24, 2017
• Journal: Ear and Hearing
• Print ISSN: 0196-0202
• Electronic ISSN: 1538-4667
• Publisher: Lippincott, Williams & Wilkins
• Peer Reviewed: Peer Reviewed
• Volume: 37
• Issue: 3
• DOI: https://doi.org/10.1097/AUD.0000000000000252
• Public URL: https://nottingham-repository.worktribe.com/output/791555
• Publisher URL: http://dx.doi.org/10.1097/AUD.0000000000000252
• Additional Information: This is not the final published version of the paper.
• Contract Date: Jan 24, 2017