Factors affecting binaural fusion in cochlear implant users.

Due to interaural frequency mismatch, bilateral cochlear-implant (CI) users may be less able to take advantage of binaural cues that normal-hearing (NH) listeners use for spatial hearing, such as interaural time differences and interaural level differences. As such, bilateral CI users have difficulty segregating competing speech even when the target and competing talkers are spatially separated. The goal of this study was to evaluate the effects of spectral resolution, tonotopic mismatch (the frequency mismatch between the acoustic center frequency assigned to CI electrode within an implanted ear relative to the expected spiral ganglion characteristic frequency), and interaural mismatch (differences in the degree of tonotopic mismatch in each ear) on speech understanding and spatial release from masking (SRM) in the presence of competing talkers in NH subjects listening to bilateral vocoder simulations. During testing, both target and masker speech were presented in five-word sentences that had the same syntax but were not necessarily meaningful. The sentences were composed of five categories in fixed order (Name, Verb, Number, Color, and Clothes), each of which had 10 items, such that multiple sentences could be generated by randomly selecting a word from each category. Speech reception thresholds (SRTs) for the target sentence presented in competing speech maskers were measured. The target speech was delivered to both ears and the two speech maskers were delivered to (1) both ears (diotic masker), or (2) different ears (dichotic masker: one delivered to the left ear and the other delivered to the right ear). Stimuli included the unprocessed speech and four 16-channel sine-vocoder simulations with different interaural mismatch (0, 1, and 2 mm). SRM was calculated as the difference between the diotic and dichotic listening conditions. With unprocessed speech, SRTs were 0.3 and -18.0 dB for the diotic and dichotic maskers, respectively. For the spectrally degraded speech with mild tonotopic mismatch and no interaural mismatch, SRTs were 5.6 and -2.0 dB for the diotic and dichotic maskers, respectively. When the tonotopic mismatch increased in both ears, SRTs worsened to 8.9 and 2.4 dB for the diotic and dichotic maskers, respectively. When the two ears had different tonotopic mismatch (e.g., there was interaural mismatch), the performance drop in SRTs was much larger for the dichotic than for the diotic masker. The largest SRM was observed with unprocessed speech (18.3 dB). With the CI simulations, SRM was significantly reduced to 7.6 dB even with mild tonotopic mismatch but no interaural mismatch; SRM was further reduced with increasing interaural mismatch. The results demonstrate that frequency resolution, tonotopic mismatch, and interaural mismatch have differential effects on speech understanding and SRM in simulation of bilateral CIs. Minimizing interaural mismatch may be critical to optimize binaural benefits and improve CI performance for competing speech, a typical listening environment. SRM (the difference in SRTs between diotic and dichotic maskers) may be a useful clinical tool to assess interaural frequency mismatch in bilateral CI users and to evaluate the benefits of optimization methods that minimize interaural mismatch.

This study aimed to characterize horizontal plane sound localization in interfering noise at different signal-to-noise ratios (SNRs) and to compare performance across normal-hearing listeners and users of unilateral and bilateral cochlear implants (CIs). CI users report difficulties with listening in noisy environments. Although their difficulties with speech understanding have been investigated in several studies, the ability to localize sounds in background noise has not extensively been examined, despite the benefits of binaural hearing being greatest in noisy situations. Sound localization is a measure of binaural processing and is thus well suited to assessing the benefit of bilateral implantation. The results will inform clinicians and implant manufacturers how to focus their efforts to improve localization with CIs in noisy situations. Six normal-hearing listeners, four unilateral, and 10 bilateral CI users indicated the perceived location of sound sources using a light pointer method. Target sounds were noise pulses played from one of 11 loudspeakers placed between -80 and +80 degrees in the frontal horizontal plane in the free field. Localization was assessed in quiet and in diffuse background noise at SNRs between +10 and -7 dB. Speech reception thresholds were measured and their relation to the localization results examined. Localization performance declined with decreasing SNR: target sounds were perceived closer to the median plane and the standard deviation of responses increased. Localization performance across groups was compared using a measure of "Spatial Resolvability" (SR). This measure gives the angular separation between two sound sources that would enable an ideal observer to correctly distinguish them 69.1% of the time. For all participants SR increased with decreasing SNR, that is, at low SNRs the spatial separation between sound sources remained distinguishable only when it was larger. Normal-hearing participants performed best, with SR between 1.4 and 5.1 degrees in quiet. Bilateral CI users showed SR between 8.3 and 43.6 degrees in quiet, corresponding approximately to the spatial resolution of normal-hearing listeners at an SNR of -5 dB. Most bilateral CI users had lost the ability to correctly determine which side the sound came from at an SNR of -3 dB. Overall, the SNR had to be at least +7 dB to achieve localization performance near to that in quiet for all bilateral CI users. No significant correlation was found between spatial resolution and speech reception thresholds, but the speech processor sensitivity setting did significantly affect performance. Unilateral CI users showed the most severe localization problems, with only two of four participants being able to correctly determine which side sounds came from in quiet. This study is the first to examine sound localization with CIs at various SNRs and to compare it with normal hearing. The results confirm that localization with CIs is strongly disrupted in noisy situations. Bilateral CIs were shown to be clearly superior over unilateral CIs for localization in quiet and in noisy situations. With bilateral CIs, localization declined at moderately high absolute noise levels (>63 dB SPL), suggesting that an extension of the acoustic-dynamic range to higher levels would be beneficial. The absence of a relation between speech reception thresholds and spatial resolution highlights the need for additional clinical tests to assess the binaural benefit of a second implant.

Music plays an important role in the daily life of cochlear implant (CI) users, but electrical hearing and speech processing pose challenges for enjoying music. Studies of unilateral CI (UCI) users’ music perception have found that these subjects have little difficulty recognizing tempo and rhythm but great difficulty with pitch, interval and melody. The present study is an initial step towards understanding music perception in bilateral CI (BCI) users. The Munich Music Questionnaire was used to investigate music listening habits and enjoyment in 23 BCI users compared to 2 control groups: 23 UCI users and 23 normal-hearing (NH) listeners. Bilateral users appeared to have a number of advantages over unilateral users, though their enjoyment of music did not reach the level of NH listeners.

This study aimed to investigate whether unilateral cochlear implant (CI) users benefit from the addition of a contralateral microphone (CI-CROS) for spatial speech recognition. Tertiary referral otology and cochlear implant center. The digits-in-noise test was used to measure speech in noise recognition abilities. Evaluations were made in 3 conditions: speech and noise presented from the front of the listener (S0N0) and with spatial separation of speech and noise (S90N-90 and S-90N90). The performance of CI patients using CI-CROS was compared with their unilateral CI condition (n = 10), normal-hearing subjects (n = 12), and bilateral CI users (n = 5). The presence and extent of several binaural phenomena (binaural summation, binaural squelch, and the better-ear effect) were evaluated. CI-CROS only provided a benefit in the listening situation wherein speech originates from the side of the CROS microphone; however, this benefit was repealed by disadvantages in other listening conditions. With CI-CROS, the hearing of patient is essentially monaural, albeit with bilateral input; therefore, patients were not able to benefit from the same binaural advantages as normal-hearing subjects and bilateral CI users. Moreover, patients using CI-CROS lost the ability to choose the optimal listening condition to perform as well as unilateral CI users. We conclude that CI-CROS is not advisable for unilateral CI users. Bilateral cochlear implantation would be a better alternative for the rehabilitation of patients with unaidable hearing on the contralateral side.

Background: The COVID-19 pandemic rapidly spread through Europe in the first months of 2020. On the 9th of March 2020, the Italian government ordered a national lock-down. The study’s objectives were: to investigate the effect of lockdown on CI users; and to detect the difference in the perception of discomfort existing between unilateral cochlear implant (UCI) users and bilateral cochlear implant (BCI) users, due to the lockdown experience. Methods: A 17-item, web-based, anonymous online survey was administered to 57 CI users, exploring hearing performance, emotions, practical issues, behavior, and tinnitus. Participation in the study was voluntary. Results: all CI users obtained an abnormal score in all questionnaire themes. For the emotion theme and the practical issue theme, the age range 61–90 showed a significant difference between UCI and BCI users in favor of BCI users (emotion theme: UCI mean = 3.9, BCI mean = 2.3, p = 0.0138; practical issues: UCI mean = 4, BCI mean = 3, p = 0.0031). Conclusions: CI users experienced the lockdown negatively as regards behavior, emotions, hearing performance, and in practical issues. CI subjects with UCI in old age suffered more from the experience of lockdown than subjects with BCI in the same age, with regards to emotions and practical issues.

Bilateral cochlear-implant (BiCI) users are less accurate at localizing free-field (FF) sound sources than normal-hearing (NH) listeners. This performance gap is not well understood but is likely due to a combination of compromises in acoustic signal representation by the two independent speech processors and neural degradation of auditory pathways associated with a patient’s hearing loss. To exclusively investigate the effect of CI speech encoding on horizontal-plane sound localization, the present study measured sound localization performance in NH subjects listening to vocoder processed and nonvocoded virtual acoustic space (VAS) stimuli. Various aspects of BiCI stimulation such as independently functioning devices, variable across-ear channel selection, and pulsatile stimulation were simulated using uncorrelated noise (Nu), correlated noise (N0), or Gaussian-enveloped tone (GET) carriers during vocoder processing. Additionally, FF sound localization in BiCI users was measured in the same testing environment for comparison. Distinct response patterns across azimuthal locations were evident for both listener groups and were analyzed using a multilevel regression analysis. Simulated implant speech encoding, regardless of carrier, was detrimental to NH localization and the GET vocoder best simulated BiCI FF performance in NH listeners. Overall, the detrimental effect of vocoder processing on NH performance suggests that sound localization deficits may persist even for BiCI patients who have minimal neural degradation associated with their hearing loss and indicates that CI speech encoding plays a significant role in the sound localization deficits experienced by BiCI users.

First, to evaluate the effect of laboratory-based test realism on speech intelligibility outcomes of cochlear implant users. Second, to conduct an exploratory investigation of speech intelligibility of cochlear implant users, including bilateral benefit, under realistic laboratory conditions. For the first goal, the authors measured speech intelligibility scores of 15 bilateral cochlear implant recipients under three different test realism levels at two different signal-to-noise ratios (SNRs). The levels included (1) standard Bamford-Kowal-Bench-like sentences with spatially separated standard babble noise; (2) standard Bamford-Kowal-Bench-like sentences with three-dimensional recordings of actual situations; and (3) a variation of the second realism level where the sentences were obtained from natural effortful conversations. For the second goal, speech intelligibility of the realistic speech material was measured in six different acoustic scenes with realistic signal-to-noise ratios ranging from -5.8 dB to 3.2 dB. Speech intelligibility was consistently highest in the most artificial (standard) test and lowest in the most realistic test. The effect of the realistic noise and that of the realistic speech material resulted in distinct SNR-dependent performance shifts with respect to their baselines. Speech intelligibility in realistic laboratory conditions was in general low, with mean scores around 60% at the highest SNR. Bilateral benefit provided on average a 7% benefit over unilateral speech understanding in the better-performing ear. The results obtained here suggest that standard speech-in-noise tests overestimate the performance of cochlear implant recipients in the real world. To address this limitation, future assessments need to improve the realism over current tests by considering the realism of both, the speech and the noise materials. Likewise, speech intelligibility data under realistic conditions suggest that, insofar as these results can be considered representative of real-life performance, conversational speech and noise levels common to cochlear implant recipients are challenging in terms of speech intelligibility, with average scores around 60%. The findings and limitations are discussed alongside the factors affecting speech intelligibility.

Objective To determine correlations between speech recognition thresholds (SRTs) for everyday sentences compared to Matrix sentences and digits-in-noise (DIN) triplets. Design Comparative analysis of SRTs across three speech materials in both cochlear implant (CI) users and typical hearing (TH) listeners, using linear regression and analysis of covariance. Study Sample 18 experienced CI users (mean age 63 ± 5 years) and 18 age-equivalent TH listeners (mean age 62 ± 12 years), all naive to the test materials. Results SRTs of Matrix sentences and everyday sentences correlated significantly (R2: 0.81 for CI, 0.71 for TH), as did SRTs of DIN triplets and everyday sentences (R2: 0.42 for CI, 0.28 for TH). Regression slopes did not differ significantly between CI and TH groups in either comparison. However, intercepts differed significantly between the CI (−2.65) and TH (−6.70) groups for the DIN triplets, but not for the Matrix sentences. Slopes for the DIN triplets deviated significantly from unity for both groups. Conclusions Dutch/Flemish Matrix sentence SRTs closely correlate with everyday sentence SRTs for both CI users and TH listeners, establishing it as a reliable alternative for repeated assessment. DIN triplet SRTs showed weaker correlations with everyday sentences and with significant intercept differences between groups.

Cochlear-implant (CI) users have difficulty understanding speech in the presence of interfering sounds. This study was designed to determine if binaural unmasking of speech is limited by peripheral or central encoding. Speech was presented to bilateral CI listeners using their clinical processors; unprocessed or vocoded speech was presented to normal-hearing (NH) listeners. Performance was worst for all listener groups in conditions where both the target and interferer were presented monaurally or diotically (i.e., no spatial differences). Listeners demonstrated improved performance compared to the monaural and diotic conditions when the target and interferer were presented to opposite ears. However, only some CI listeners demonstrated improved performance if the target was in one ear and the interferer was presented diotically, and there was no change for the group on average. This is unlike the 12-dB benefit observed in the NH group when presented the CI simulation. The results suggest that CI users can direct attention to a target talker if the target and interferer are presented to opposite ears; however, larger binaural benefits are limited for more realistic listening configurations, likely due to the imprecise peripheral encoding of the two sounds.

Cochlear implant (CI) trends are changing as more recipients are receiving bilateral implantation. Also more pre-lingually deafened adults are choosing to be implanted. Clinical assessment after cochlear implantation is usually based on speech perception tests. Such tests, however, may not be a realistic outcome measure for some of these cases, creating a need for more objective measures of CI performance. Cortical auditory evoked potentials (CAEPs) recorded in the sound field may be a fast and reliable procedure for the clinical audiologist to determine CI outcomes. This paper presents two case studies illustrating CAEP findings in an adult CI user who was pre-lingually deafened and a bilateral CI user. Copyright © 2009 John Wiley & Sons, Ltd.

Plain Language SummaryCochlear implantation is the standard treatment for severe to profound hearing loss. While cochlear implant (CI) users can communicate effectively in quiet environments, speech understanding in noise remains challenging. Bimodal hearing, combining a CI in one ear and a hearing aid (HA) in the other, has shown advantages over unilateral electrical hearing, especially for speech understanding in noisy conditions. We analyzed the effect of the addition of the HA to the CI in this paper. There are also other processing techniques available to improve speech understanding in noise for this population. In this paper, one of these techniques, beamforming, is studied in different configurations. Therefore, 17 participants with a CI in one ear and a HA in the other ear are included. They performed a speech test for different configurations with and without beamforming to be able to analyze the effect of beamforming.

For bilateral cochlear implant (CI) patients, electrodes that receive the same frequency allocation often stimulate locations in the left and right ear that do not yield the same perceived pitch, resulting in a pitch mismatch. This pitch mismatch may be related to degraded binaural abilities. Pitch mismatches have been found for some bilateral CI users and the goal of this study was to determine whether pitch mismatches are prevalent in bilateral CI patients, including those with extensive experience with bilateral CIs. To investigate this possibility, pitch matching was conducted with 16 bilateral CI patients. For 14 of the 16 participants, there was a significant difference between those electrodes in the left and right ear that yielded the same pitch and those that received the same frequency allocation in the participant’s clinical map. The results suggest that pitch mismatches are prevalent with bilateral CI users. The results also indicated that pitch mismatches persist even with extended bilateral CI experience. Such mismatches may reduce the benefits patients receive from bilateral CIs.

To evaluate the listening conditions of bilateral cochlear implant (CI) users in their daily living environment. Retrospective study. University hospital. Thirty-one adult CI users 16 years or older; 18 underwent sequential surgery, and 13 underwent simultaneous surgery. Inclusion criteria included the availability of CI data logging features and a minimum duration of binaural use of 6 months. Retrospective analysis of data obtained from the automatic scene classifier data logging system. Comparison of data logging and maximum speech discrimination scores of the two surgery groups (sequential vs. simultaneous) to investigate the potential influence of these factors on the listening conditions of CI users. The maximum speech discrimination score of the second CI in the sequential group was significantly worse than that of any other CI in the sequential and simultaneous CI groups. Additionally, the longer the interval between surgeries, the more significant the difference in "time on air" between the first and the second CIs. The second CI in sequential CI surgery had a shorter "time on air" than the first or the bilateral simultaneous CIs; the second CI was also used more frequently in noisy and speech with background noise environments. A second CI may be more frequently used in challenging listening environments because of its binaural auditory effect, despite its lower speech discrimination performance. The timing of sequential implantation and the potential impact of binaural hearing should be considered when developing rehabilitation strategies for individuals with bilateral CIs.

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An intact auditory system is essential for the development and maintenance of voice quality and speech prosody. On the contrary hearing loss affects the adjustments and appropriate use of organs involved in speech and voice production. Spectro-acoustic voice parameters have been evaluated in Cochlear Implant (CI) users, and the authors of previous systematic reviews on the topic concluded that fundamental frequency (F0) seemed preliminarily the most reliable parameter to evaluate voice alterations in adult CI users. The main aim of this systematic review and meta-analysis was to clarify the vocal parameters and prosodic alterations of speech in pediatric CI users. The protocol of the systematic review was registered on the PROSPERO database, International prospective register of systematic reviews. We conducted a search of the English literature published in the period between January 1, 2005 and April 1, 2022 on the Pubmed and Scopus databases. A meta-analysis was conducted to compare the values of voice acoustic parameters in CI users and non-hearing-impaired controls. The analysis was conducted using the standardized mean difference as the outcome measure. A random-effects model was fitted to the data. A total of 1334 articles were initially evaluated using title and abstract screening. After applying inclusion/exclusion criteria, 20 articles were considered suitable for this review. The age of the cases ranged between 25 and 132 months at examination. The most studied parameters were F0, Jitter, Shimmer and Harmonics-to-Noise Ratio (HNR); other parameters were seldom reported. A total of 11 studies were included in the meta-analysis of F0, with the majority of estimates being positive (75%); the estimated average standardized mean difference based on the random-effects model was 0.3033 (95% CI: 0.0605 to 0.5462; P = 0.0144). For Jitter (0.2229; 95% CI: -0.1862 to 0.7986; P = 0.2229) and shimmer (0.2540; 95% CI: -0.1404 to 0.6485; P = 0.2068) there was a trend toward positive values without reaching statistical significance. This meta-analysis confirmed that higher F0 values have been observed in the pediatric population of CI users compared to age-matched normal hearing volunteers, whereas the parameters of voice noise were not significantly different between cases and controls. Prosodic aspects of language need further investigations. In longitudinal contexts, prolonged auditory experience with CI has brought voice parameters closer to the norm. Following the available evidence, we stress the utility of inclusion of vocal acoustic analysis in the clinical evaluation and follow-up of CI patients to optimize the rehabilitation process of pediatric patients with hearing loss.