Sound Localization in Noise by Normal-Hearing Listeners and 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.

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.

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.

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.

Factors affecting binaural fusion in cochlear implant users.

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.

Spatial hearing in children with bilateral cochlear implants (BCIs) was assessed by: (a) comparing localization of stationary and moving sound, (b) investigating the relationship between sound localization and sensitivity to interaural level and timing differences (ILDs/ITDs), (c) evaluating effects of aural preference on sound localization, and (d) exploring head and eye (gaze) movements during sound localization. Children with BCIs (n = 42, MAge = 12.3 years) with limited duration of auditory deprivation and peers with typical hearing (controls; n = 37, MAge = 12.9 years) localized stationary and moving sound with unrestricted head and eye movements. Sensitivity to binaural cues was measured by a lateralization task to ILDs and ITDs. Spatial separation effects were measured by spondee-word recognition thresholds (SNR thresholds) when noise was presented in front (colocated/0°) or with 90° of left/right separation. BCI users had good speech reception thresholds (SRTs) in quiet but higher SRTs in noise than controls. Spatial separation of noise from speech revealed a greater advantage for the right ear across groups. BCI users showed increased errors localizing stationary sound and detecting moving sound direction compared to controls. Decreased ITD sensitivity occurred with poorer localization of stationary sound in BCI users. Gaze movements in BCI users were more random than controls for stationary and moving sounds. BCIs support symmetric hearing in children with limited duration of auditory deprivation and promote spatial hearing which is albeit impaired. Spatial hearing was thus considered to be “emerging.” Remaining challenges may reflect disruptions in ITD sensitivity and ineffective gaze movements.

Objectives To perform a systematic literature review (SLR) on hearing and quality-of-life (QoL) benefits of bilateral versus unilateral cochlear implants (CIs) in adults with sensorineural hearing loss (SNHL), and to quantify benefits through a meta-analysis when feasible. Methods Embase, MEDLINE, and Cochrane were searched from January 2005–June 2022. Eligible studies presented effectiveness of CIs and/or QoL of adult CI users. Articles that presented numerical point estimates for, or numerical difference between, bilateral and unilateral CI, and measures of uncertainty were considered for meta-analysis, with data analyzed using fixed- and random-effects models. Results Thirty-five articles were included. There was a trend of significant improvement with bilateral CIs in sound localization and binaural redundancy. A meta-analysis confirmed statistically significant benefits in speech perception (in quiet, 12.6 percentage point [95% confidence interval: 7.1, 18.1] improvement; in noise, improvement in speech reception threshold of 1.5 dB signal-to-noise ratio [–1.5 dB; 95% confidence interval: −2.5, −0.4]). There were beneficial trends of bilateral CIs regarding head-shadow effect and binaural release from masking. Significant improvements in hearing-specific QoL were observed; generic QoL was mostly unchanged. Discussion Bilateral CIs provide audiological benefit over unilateral CI, resulting in hearing-specific QoL improvements. Lack of changes in generic QoL may reflect that instrument domains are insensitive to hearing-related changes when going from unilateral to bilateral CIs. Meta-analyses could not be performed for all hearing and QoL outcomes owing to variability in methodologies across studies. Conclusions These findings should be used to inform clinical decision-making to ensure the best outcomes for adults with bilateral SNHL.

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.

Two are better than one: Differences in cortical EEG patterns during auditory and visual verbal working memory processing between Unilateral and Bilateral Cochlear Implanted children

School closures and other COVID-19-related restrictions could decrease children's exposure to speech during important stages of development. To assess whether significant decreases in exposure to spoken communication found during the initial phase of the COVID-19 pandemic among children using cochlear implants are confirmed for a larger cohort of children and were sustained over the first years of the COVID-19 pandemic. This cohort study used datalogs collected from children with cochlear implants during clinical visits to a tertiary pediatric hospital in Toronto, Ontario, Canada, from January 1, 2018, to November 11, 2021. Children with severe to profound hearing loss using cochlear implants were studied because their devices monitored and cataloged levels and types of sounds during hourly use per day (datalogs) and because their hearing and spoken language development was particularly vulnerable to reduced sound exposure. Statistical analyses were conducted between January 2022 and August 2023. Daily hours of sound were captured by the cochlear implant datalogging system and categorized into 6 auditory scene categories, including speech and speech-in-noise. Time exposed to speech was calculated as the sum of daily hours in speech and daily hours in speech-in-noise. Residual hearing in the ear without an implant of children with unilateral cochlear implants was measured by pure tone audiometry. Mixed-model regression analyses revealed main effects with post hoc adjustment of 95% CIs using the Satterthwaite method. Datalogs (n = 2746) from 262 children (137 with simultaneous bilateral cochlear implants [74 boys (54.0%); mean (SD) age, 5.8 (3.5 years)], 38 with sequential bilateral cochlear implants [24 boys (63.2%); mean (SD) age, 9.1 (4.2) years], and 87 with unilateral cochlear implants [40 boys (46.0%); mean (SD) age, 7.9 (4.6) years]) who were preschool aged (n = 103) and school aged (n = 159) before the COVID-19 pandemic were included in analyses. There was a slight increase in use among preschool-aged bilateral cochlear implant users through the pandemic (early pandemic, 1.4 h/d [95% CI, 0.3-2.5 h/d]; late pandemic, 2.3 h/d [95% CI, 0.6-4.0 h/d]) and little change in use among school-aged bilateral cochlear implant users (early pandemic, -0.6 h/d [95% CI, -1.1 to -0.05 h/d]; late pandemic, -0.3 h/d [95% CI, -0.9 to 0.4 h/d]). However, use decreased during the late pandemic period among school-aged children with unilateral cochlear implants (-1.8 h/d [95% CI,-3.0 to -0.6 h/d]), particularly among children with good residual hearing in the ear without an implant. Prior to the pandemic, children were exposed to speech for approximately 50% of the time they used their cochlear implants (preschool-aged children: bilateral cochlear implants, 46.6% [95% CI, 46.5%-47.2%] and unilateral cochlear implants, 52.1% [95% CI, 50.7%-53.5%]; school-aged children: bilateral cochlear implants, 47.6% [95% CI, 46.8%-48.4%] and unilateral cochlear implants, 51.0% [95% CI, 49.4%-52.6%]). School-aged children in both groups experienced significantly decreased speech exposure in the early pandemic period (bilateral cochlear implants, -12.1% [-14.6% to -9.4%]; unilateral cochlear implants, -15.5% [-20.4% to -10.7%]) and late pandemic periods (bilateral cochlear implants, -5.3% [-8.0% to -2.6%]; unilateral cochlear implants, -11.2% [-15.3% to -7.1%]) compared with the prepandemic baseline. This cohort study using datalogs from children using cochlear implants suggests that a sustained reduction in children's access to spoken communication was found during more than 2 years of COVID-19 pandemic-related lockdowns and school closures.

Bilateral implant recipients theoretically have access to binaural cues. Research in postlingually deafened adults with cochlear implants (CIs) indicates minimal evidence for true binaural hearing. Congenitally deafened children who experience spatial hearing with bilateral CIs, however, might perceive binaural cues in the CI signal differently. There is limited research examining binaural hearing in children with CIs, and the few published studies are limited by the use of unrealistic speech stimuli and background noise. The purposes of this study were to (1) replicate our previous study of binaural hearing in postlingually deafened adults with AzBio sentences in prelingually deafened children with the pediatric version of the AzBio sentences, and (2) replicate previous studies of binaural hearing in children with CIs using more open-set sentences and more realistic background noise (i.e., multitalker babble). The study was a within-participant, repeated-measures design. The study sample consisted of 14 children with bilateral CIs with at least 25 mo of listening experience. Speech recognition was assessed using sentences presented in multitalker babble at a fixed signal-to-noise ratio. Test conditions included speech at 0° with noise presented at 0° (S0N0), on the side of the first CI (90° or 270°) (S0N1stCI), and on the side of the second CI (S0N2ndCI) as well as speech presented at 0° with noise presented semidiffusely from eight speakers at 45° intervals. Estimates of summation, head shadow, squelch, and spatial release from masking were calculated. Results of test conditions commonly reported in the literature (S0N0, S0N1stCI, S0N2ndCI) are consistent with results from previous research in adults and children with bilateral CIs, showing minimal summation and squelch but typical head shadow and spatial release from masking. However, bilateral benefit over the better CI with speech at 0° was much larger with semidiffuse noise. Congenitally deafened children with CIs have similar availability of binaural hearing cues to postlingually deafened adults with CIs within the same experimental design. It is possible that the use of realistic listening environments, such as semidiffuse background noise as in Experiment II, would reveal greater binaural hearing benefit for bilateral CI recipients. Future research is needed to determine whether (1) availability of binaural cues for children correlates with interaural time and level differences, (2) different listening environments are more sensitive to binaural hearing benefits, and (3) differences exist between pediatric bilateral recipients receiving implants in the same or sequential surgeries.

On the relationship between auditory cognition and speech intelligibility in cochlear implant users: An ERP study

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.

The present research asks whether two tactile aids with directional microphones, by providing additional inter-channel level information and etc., could help unilateral cochlear implant (CI) localize sound sources. For normal hearing subjects, sound source localization based on tactile vibration cues alone can be as accurate as auditory localization in the frontal horizontal plane (Gescheider, 1970). CI users may as well benefit from additional tactile aids just as normal hearing people do. The current study uses two bone-anchored hearing aids (BAHA) as sources of tactile vibration. The two BAHAs, bonded together by a special gadget to maintain a particular distance and angle, both have directional microphones, and are programed so that one point to the front-left side and the other to the front-right side. Unilateral CI users voluntarily participated in the experimental study. Wide band noise stimuli were presented at 65 dB SPL. The subjects hold one BAHA in each hand and do localization tasks with (1) CI only and (2) with CI and tactile sensation combined. Preliminary data shows CI users can get some benefit from the additional information provided by tactile aids in 360 degree localization (45 degree spacing) on the horizontal plane.