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Binaural Optimization of Cochlear Implants: Discarding Frequency Content Without Sacrificing Head-Shadow Benefit
Sterling W Sheffield1,2, Matthew J Goupell3, Nathaniel J Spencer4
1Department of Speech, Language, and Hearing Sciences, University of Florida, Gainesville, Florida, USA.
Ear and Hearing
|August 23, 2019
Summary
Cochlear implant users with single-sided deafness (SSD-CI) and bilateral cochlear implants (BI-CI) can have frequencies removed from their poorer-hearing ear without losing head-shadow benefits. This flexibility aids binaural fitting strategies to reduce interaural mismatch.
Area of Science:
- Audiology and Hearing Science
- Biomedical Engineering
- Neuroscience
Background:
- Single-sided deafness cochlear-implant (SSD-CI) and bilateral cochlear-implant (BI-CI) listeners achieve good head-shadow benefits but limited binaural benefits.
- Limited binaural benefits may stem from cochlear place of stimulation mismatches between ears.
- Binaural fitting strategies reallocating frequencies could reduce mismatch but risk monaural speech recognition and head-shadow benefits.
Purpose of the Study:
- To determine the extent of frequency information exclusion from the poorer-hearing ear CI without reducing head-shadow benefits.
- To investigate how interaural asymmetry in monaural speech recognition influences these outcomes.
- To explore potential benefits of frequency reallocation in binaural CI fitting.
Main Methods:
- Speech-recognition thresholds were measured in noise for SSD-CI, BI-CI, and normal-hearing listeners using vocoder simulations.
- Stimuli were presented with head-related impulse-response simulations, varying signal and noise locations to create a better signal-to-noise ratio (SNR) at the poorer-hearing ear.
- Systematic high-pass and low-pass filtering of the poorer-ear CI signal was applied to assess the impact on head-shadow benefit.
Main Results:
- Mean head-shadow benefit was approximately 7 dB for SSD-CI listeners and 14 dB for BI-CI listeners.
- Frequencies below 1236 Hz could be excluded for SSD-CI listeners, and below 886 Hz or above 3814 Hz for BI-CI listeners, without loss of head-shadow benefit.
- Bilateral performance was more robust to filtering than monaural performance, and greater interaural asymmetry in monaural performance correlated with less head-shadow benefit.
Conclusions:
- Significant frequency ranges can be excluded from the poorer-ear CI in SSD-CI and BI-CI listeners without compromising head-shadow benefit.
- This flexibility supports binaural programming solutions aimed at reducing interaural frequency mismatch.
- Treating the auditory system as a single unit allows for discarding redundant frequency information from one CI, enhancing binaural fitting.
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