Dataset Information

Binaural Pitch Fusion: Binaural Pitch Averaging in Cochlear Implant Users With Broad Binaural Fusion.

ABSTRACT:

Objectives

Individuals who use hearing aids (HAs) or cochlear implants (CIs) can experience broad binaural pitch fusion, such that sounds differing in pitch by as much as 3 to 4 octaves are perceptually integrated across ears. Previously, it was shown in HA users that the fused pitch is a weighted average of the two monaural pitches, ranging from equal weighting to dominance by the lower pitch. The goal of this study was to systematically measure the fused pitches in adult CI users, and determine whether CI users experience similar pitch averaging effects as observed in HA users.

Design

Twelve adult CI users (Cochlear Ltd, Sydney, Australia) participated in this study: six bimodal CI users, who wear a CI with a contralateral HA, and six bilateral CI users. Stimuli to HA ears were acoustic pure tones, and stimuli to CI ears were biphasic pulse trains delivered to individual electrodes. Fusion ranges, the ranges of frequencies/electrodes in the comparison ear that were fused with a single electrode (electrode 22, 18, 12, or 6) in the reference ear, were measured using simultaneous, dichotic presentation of reference and comparison stimuli in opposite ears, and varying the comparison stimulus. Once the fusion ranges were measured, the fused binaural pitch of a reference-pair stimulus combination was measured by finding a pitch match to monaural comparison stimuli presented to the paired stimulus ear.

Results

Fusion pitch weighting in CI users varied depending on the pitch difference of the reference-pair stimulus combination, with equal pitch averaging occurring for stimuli closer in pitch and lower pitch dominance occurring for stimuli farther apart in pitch. The averaging region was typically 0.5 to 2.3 octaves around the reference for bimodal CI users and 0.4 to 1.5 octaves for bilateral CI users. In some cases, a bias in the averaging region was observed toward the ear with greater stimulus variability.

Conclusions

Fusion pitch weighting effects in CI users were similar to those observed previously in HA users. However, CI users showed greater inter-subject variability in both pitch averaging ranges and bias effects. These findings suggest that binaural pitch averaging could be a common underlying mechanism in hearing-impaired listeners.

SUBMITTER: Oh Y

PROVIDER: S-EPMC7501189 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:OBJECTIVES:When listening to two competing speakers, normal-hearing (NH) listeners can take advantage of voice differences between the speakers. Users of cochlear implants (CIs) have difficulty in perceiving speech on speech. Previous literature has indicated sensitivity to voice pitch (related to fundamental frequency, F0) to be poor among implant users, while sensitivity to vocal-tract length (VTL; related to the height of the speaker and formant frequencies), the other principal voice characteristic, has not been directly investigated in CIs. A few recent studies evaluated F0 and VTL perception indirectly, through voice gender categorization, which relies on perception of both voice cues. These studies revealed that, contrary to prior literature, CI users seem to rely exclusively on F0 while not utilizing VTL to perform this task. The objective of the present study was to directly and systematically assess raw sensitivity to F0 and VTL differences in CI users to define the extent of the deficit in voice perception. DESIGN:The just-noticeable differences (JNDs) for F0 and VTL were measured in 11 CI listeners using triplets of consonant-vowel syllables in an adaptive three-alternative forced choice method. RESULTS:The results showed that while NH listeners had average JNDs of 1.95 and 1.73 semitones (st) for F0 and VTL, respectively, CI listeners showed JNDs of 9.19 and 7.19 st. These JNDs correspond to differences of 70% in F0 and 52% in VTL. For comparison to the natural range of voices in the population, the F0 JND in CIs remains smaller than the typical male-female F0 difference. However, the average VTL JND in CIs is about twice as large as the typical male-female VTL difference. CONCLUSIONS:These findings, thus, directly confirm that CI listeners do not seem to have sufficient access to VTL cues, likely as a result of limited spectral resolution, and, hence, that CI listeners' voice perception deficit goes beyond poor perception of F0. These results provide a potential common explanation not only for a number of deficits observed in CI listeners, such as voice identification and gender categorization, but also for competing speech perception.

Project description:ImportanceCochlear implant users generally display poor pitch perception. Flat-panel computed tomography (FPCT) has recently emerged as a modality capable of localizing individual electrode contacts within the cochlea in vivo. Significant place-pitch mismatch between the clinical implant processing settings given to patients and the theoretical maps based on FPCT imaging has previously been noted.ObjectiveTo assess whether place-pitch mismatch is associated with poor cochlear implant-mediated pitch perception through evaluation of an individualized, image-guided approach toward cochlear implant programming on speech and music perception among cochlear implant users.Design, setting, and participantsA prospective cohort study of 17 cochlear implant users with MED-EL electrode arrays was performed at a tertiary referral center. The study was conducted from June 2016 to July 2017.InterventionsTheoretical place-pitch maps using FPCT secondary reconstructions and 3-dimensional curved planar re-formation software were developed. The clinical map settings (eg, strategy, rate, volume, frequency band range) were modified to keep factors constant between the 2 maps and minimize confounding. The acclimation period to the maps was 30 minutes.Main outcomes and measuresParticipants performed speech perception tasks (eg, consonant-nucleus-consonant, Bamford-Kowal-Bench Speech-in-Noise, vowel identification) and a pitch-scaling task while using the image-guided place-pitch map (intervention) and the modified clinical map (control). Performance scores between the 2 interventions were measured.ResultsOf the 17 participants, 10 (58.8%) were women; mean (SD) was 59 (11.3) years. A significant median increase in pitch scaling accuracy was noted when using the experimental map compared with the control map (4 more correct answers; 95% CI, 0-8). Specifically, the number of pitch-scaling reversals for notes spaced at 1.65 semitones or greater decreased when an image-based approach to cochlear implant programming was used vs the modified clinical map (4 mistakes; 95% CI, 0.5-7). Although there was no observable median improvement in speech perception during use of an image-based map, the acute changes in frequency allocation and electrode channel deactivations used with the image-guided maps did not worsen consonant-nucleus-consonant (-1% correct phonemes, 95% CI, -2.5% to 6%) and Bamford-Kowal-Bench Speech-in-Noise (0.5-dB difference; 95% CI, -0.75 to 2.25 dB) median performance results relative to the clinical maps used by the patients.Conclusions and relevanceAn image-based approach toward ochlear implant mapping may improve pitch perception outcomes by reducing place-pitch mismatch. Studies using a longer acclimation period with chronic stimulation over months may help assess the full range of the benefits associated with personalized image-guided cochlear implant mapping.