Benefits to Speech Perception in Noise From the Binaural Integration of Electric and Acoustic Signals in Simulated Unilateral Deafness

Abstract

Objectives:This study used vocoder simulations with normal-hearing (NH) listeners to (1) measure their ability to integrate speech information from an NH ear and a simulated cochlear implant (CI), and (2) 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 eight-channel noise vocoder with one of the 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. The advantages of binaural integration 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 the 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 an NH 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 that have measured the speech perception of unilaterally deaf individuals after CI but with nonindividual...

Interaural Time-Difference Discrimination as a Measure of Place of Stimulation for Cochlear-Implant Users With Single-Sided Deafness

“…The ability to perceptually fuse speech signals presented to the two ears is a critical step in organizing the auditory scene. Vocoder simulations have suggested that interaural place mismatch might be detrimental to this process ( Ma et al., 2016 ; Wess et al., 2017 ). Siciliano, Faulkner, Rosen, and Mair (2010) found that extensive training could not improve speech perception for interaurally mismatched vocoders, in contrast to the improvement that has been demonstrated for spectrally shifted monaurally vocoded speech ( Rosen et al., 1999 ).…”

“…NH listeners show reduced ILD sensitivity for frequency-mismatched uncorrelated noise bands ( Francart & Wouters, 2007 ) and acoustic pulse trains ( Goupell, Stoelb, Kan, & Litovsky, 2013 ). Vocoder simulations of SSD-CI listening have shown that interaural place mismatch can reduce subjectively reported binaural fusion ( Aronoff, Shayman, Prasad, Suneel, & Stelmach, 2015 ; Suneel, Staisloff, Shayman, Stelmach, & Aronoff, 2017 ), the binaural integration of speech information ( Ma, Morris, & Kitterick, 2016 ), and the ability to perceptually separate concurrent speech ( Wess et al., 2017 ). These results suggest that SSD-CI listeners might benefit if the CI frequency-allocation table (FAT) were adjusted to deliver each acoustic frequency to the electrode that is stimulating the spiral ganglia corresponding to the basilar membrane location that is naturally tuned to that frequency.…”

Interaural Time Difference Perception with a Cochlear Implant and a Normal Ear

“…If a subject is not sufficiently sensitive to ITD, matching the place of stimulation across cochleae might still be beneficial for speech intelligibility or binaural unmasking (Ma et al, 2016; Wess et al, 2017). …”

Effects of Cochlear Implantation on Binaural Hearing in Adults With Unilateral Hearing Loss

“…It has also been argued that binaural hearing in patients with a unilateral CI and contralateral acoustic hearing is limited by the asymmetry between ears, particularly with respect to the mapping of frequency to place of excitation in the cochlea ( Wess, Brungart, & Bernstein, 2017 ). These asymmetries could interfere with binaural fusion, which is thought to be a prerequisite for the optimal use of binaural spatial cues ( Kan, Stoelb, Litovsky, & Goupell, 2013 ; Ma, Morris, & Kitterick, 2016 ; Suneel, Staisloff, Shayman, Stelmach, & Aronoff, 2017 ).…”