Restoration of cortical symmetry and binaural function: Cortical auditory evoked responses in adult cochlear implant users with single sided deafness

Cortical temporal mismatch compensation in bimodal cochlear implant users: Selective attention decoding and pupillometry study

Bimodal cochlear implant (CI) users combine electrical stimulation from a CI in one ear with acoustic stimulation through either normal hearing or a hearing aid in the opposite ear. While this bimodal stimulation typically improves speech perception, the degree of improvement varies significantly and can sometimes result in interference effects. This variability is associated with the integration of electric and acoustic signals, which can be influenced by several factors, including temporal mismatch between the two sides. In previous work, we utilized cortical auditory evoked potentials (CAEPs) to estimate the temporal mismatch between the CI stimulation (CIS) side and the acoustic stimulation (AS) side, based on differences in N1 latencies when listening with the CIS alone and the AS alone. Building on this approach, the present study estimates individual temporal mismatch at cortical level through N1 latency of CAEPs and investigates the impact of compensating for this mismatch on speech perception. Behavioral and objective measures of speech perception were conducted in bimodal CI users under three bimodal listening conditions: clinical setting, a setting with compensated temporal mismatch between electric and acoustic stimulation and a setting with a large temporal mismatch of 50 ms between electric and acoustic stimulation. The behavioral measure consisted of a speech understanding test. Objective measures included pupillometry, electroencephalography (EEG) based on cortical auditory evoked potentials (CAEPs), EEG based on selective attention decoding including analysis of parietal alpha power. No significant effect of listening condition on behavioral speech understanding performance was observed, even for the condition with a large temporal mismatch of 50 ms. Similarly, pupillometry did not reveal a significant difference across listening conditions, although it was found to be related to behavioral speech understanding. N1P2 amplitude of CAEPs was greatest under the condition with compensated temporal mismatch. The phase-locking value of CAEPs, the temporal response function related to selective attention decoding, and parietal alpha power all showed a significant improvement when applying temporal mismatch compensation, compared to the condition with a substantial 50 ms temporal mismatch. However, these metrics did not exhibit significant effects when compared to the standard clinical setting condition. These findings emphasize that neural metrics are more sensitive than behavioral measures in detecting interaural mismatch effects. A significant enhancement of CAEPs N1P2 amplitude compared to clinical setting was observed. Other neural metrics showed a limited improvement with compensated listening condition, suggesting insufficient compensation solely in temporal domain.

The temporal mismatch across listening sides affects cortical auditory evoked responses in normal hearing listeners and cochlear implant users with contralateral acoustic hearing

Combining a cochlear implant with contralateral acoustic hearing typically enhances speech understanding, although this improvement varies among CI users and can lead to an interference effect. This variability may be associated with the effectiveness of the integration between electric and acoustic stimulation, which might be affected by the temporal mismatch between the two listening sides. Finding methods to compensate for the temporal mismatch might contribute to the optimal adjustment of bimodal devices and to improve hearing in CI users with contralateral acoustic hearing. The current study investigates cortical auditory evoked potentials (CAEPs) in normal hearing listeners (NH) and CI users with contralateral acoustic hearing. In NH, the amplitude of the N1 peak and the maximum phase locking value (PLV) were analyzed under monaural, binaural, and binaural temporally mismatched conditions. In CI users, CAEPs were measured when listening with CI only (CIS_only), acoustically only (AS_only) and with both sides together (CIS+AS). When listening with CIS+AS, various interaural delays were introduced between the electric and acoustic stimuli. In NH listeners, interaural temporal mismatch resulted in decreased N1 amplitude and PLV. Moreover, PLV is suggested as a more sensitive measure to investigate the integration of information between the two listening sides. CI users showed varied N1 latencies between the AS_only and CIS_only listening conditions, with increased N1 amplitude when the temporal mismatch was compensated. A tendency towards increased PLV was also observed, however, to a lesser extent than in NH listeners, suggesting a limited integration between electric and acoustic stimulation. This work highlights the potential of CAEPs measurement to investigate cortical processing of the information between two listening sides in NH and bimodal CI users.

Biomarkers of auditory cortical plasticity and development of binaural pathways in children with unilateral hearing loss using a hearing aid

Congenital or early-onset unilateral hearing loss (UHL) can disrupt the normal development of the auditory system. In extreme cases of UHL (i.e., single sided deafness), consistent cochlear implant use during sensitive periods resulted in cortical reorganization that partially reversed the detrimental effects of unilateral sensory deprivation. There is a gap in knowledge, however, regarding cortical plasticity i.e. the brain's capacity to adapt, reorganize, and develop binaural pathways in milder degrees of UHL rehabilitated by a hearing aid (HA). The current study was set to investigate early-stage cortical processing and electrophysiological manifestations of binaural processing by means of cortical auditory evoked potentials (CAEPs) to speech sounds, in children with moderate to severe-to-profound UHL using a HA. Fourteen children with UHL (CHwUHL), 6-14 years old consistently using a HA for 3.5 (±2.3) years participated in the study. CAEPs were elicited to the speech sounds /m/, /g/, and /t/ in three listening conditions: monaural [Normal hearing (NH), HA], and bilateral [BI (NH + HA)]. Results indicated age-appropriate CAEP morphology in the NH and BI listening conditions in all children. In the HA listening condition: (1) CAEPs showed similar morphology to that found in the NH listening condition, however, the mature morphology observed in older children in the NH listening condition was not evident; (2) P1 was elicited in all but two children with severe-to-profound hearing loss, to at least one speech stimuli, indicating effective audibility; (3) A significant mismatch in timing and synchrony between the NH and HA ear was found; (4) P1 was sensitive to the acoustic features of the eliciting stimulus and to the amplification characteristics of the HA. Finally, a cortical binaural interaction component (BIC) was derived in most children. In conclusion, the current study provides first-time evidence for cortical plasticity and partial reversal of the detrimental effects of moderate to severe-to-profound UHL rehabilitated by a HA. The derivation of a cortical biomarker of binaural processing implies that functional binaural pathways can develop when sufficient auditory input is provided to the affected ear. CAEPs may thus serve as a clinical tool for assessing, monitoring, and managing CHwUHL using a HA.

Auditory Cortical Plasticity in Patients with Single-Sided Deafness Before and After Cochlear Implantation

PURPOSE

This study investigated neuroplastic changes induced by postlingual single-sided deafness (SSD) and the effects of a cochlear implantation for the deaf ear. Neural processing of acoustic signals from the normal hearing ear to the brain was studied before and after implantation using a positron emission tomography (PET)/CT scanner.

METHODS

Eight patients with postlingual SSD received a cochlear implant (CI) in a prospective clinical trial. Dynamic imaging was performed in a PET/CT scanner using radioactively labeled water ([15O]H2O) to localize changes in the regional cerebral blood flow (rCBF) with and without an auditory task of logatomes containing speech-like elements without meaningful context. The normal hearing ear was stimulated before implantation and after the use of the cochlear implant for at least 8 months (mean 13.5, range 8.1-26.6). Eight age- and gender-matched subjects with normal hearing on both sides served as healthy control subjects (HCS).

RESULTS

When the normal hearing ear of SSD patients was stimulated before CI implantation, the [15O]H2O-PET showed a more symmetrical rCBF in the auditory regions of both hemispheres in comparison to the HCS. The use of CI increased the asymmetry index (AI) in six of eight patients indicating an increase of activity of the contralateral hemisphere. Non-parametric statistics revealed a significant difference in the AI between patients before CI implantation and HCS (p < .01), which disappeared after CI implantation (p = .195).

CONCLUSION

The functional neuroimaging data showed a tendency towards normalization of neuronal activity after CI implantation, which supports the effectiveness of CI in SSD patients.

TRIAL REGISTRATION

ClinicalTrials.gov Identifier: NCT01749592, December 13, 2012.

A Study of Event-Related Potentials During Monaural and Bilateral Hearing in Single-Sided Deaf Cochlear Implant Users

OBJECTIVES

Single-sided deafness (SSD) is characterized by a profoundly deaf ear and normal hearing in the contralateral ear. A cochlear implant (CI) is the only method to restore functional hearing in a profoundly deaf ear. In a previous study, we identified that the cortical processing of a CI signal differs from the normal-hearing ear (NHE) when directly compared using an auditory oddball paradigm consisting of pure tones. However, exactly how the brain integrates the electrical and acoustic signal is not well investigated. This study aims to understand how the provision of the CI in combination with the NHE may improve SSD CI users' ability to discriminate and evaluate auditory stimuli.

DESIGN

Electroencephalography from 10 SSD-CI participants (4 participated in the previous pure-tone study) were recorded during a semantic acoustic oddball task, where they were required to discriminate between odd and even numbers. Stimuli were presented in four hearing conditions: directly through the CI, directly to the NHE, or in free field with the CI switched on and off. We examined task-performance (response time and accuracy) and measured N1, P2, N2N4, and P3b event-related brain potentials (ERPs) linked to the detection, discrimination, and evaluation of task relevant stimuli. Sound localization and speech in noise comprehension was also examined.

RESULTS

In direct presentation, task performance was superior during NHE compared with CI (shorter and less varied reaction times [~720 versus ~842 msec], higher target accuracy [~93 versus ~70%]) and early neural responses (N1 and P2) were enhanced for NHE suggesting greater signal saliency. However, the size of N2N4 and P3b target-standard effects did not differ significantly between NHE and CI. In free field, target accuracy was similarly high with the CI (FF-On) and without the CI (FF-Off) (~95%), with some evidence of CI interference during FF-On (more variable and slightly but significantly delayed reaction times [~737 versus ~709 msec]). Early neural responses and late effects were also greater during FF-On. Performance on sound localization and speech in noise comprehension (S CI N NHE configuration only) was significantly greater during FF-On.

CONCLUSIONS

Both behavioral and neural responses in the semantic oddball task were sensitive to CI in both direct and free-field presentations. Direct conditions revealed that participants could perform the task with the CI alone, although performance was suboptimal and early neural responses were reduced when compared with the NHE. For free-field, the addition of the CI was associated with enhanced early and late neural responses, but this did not result in improved task performance. Enhanced neural responses show that the additional input from the CI is modulating relevant perceptual and cognitive processes, but the benefit of binaural hearing on behavior may not be realized in simple oddball tasks which can be adequately performed with the NHE. Future studies interested in binaural hearing should examine performance under noisy conditions and/or use spatial cues to allow headroom for the measurement of binaural benefit.

Cochlear Implantation Outcomes in Adults With Single-Sided Deafness: A Systematic Review and Meta-analysis

OBJECTIVE

To assess spatial hearing, tinnitus, and quality-of-life outcomes in adults with single-sided deafness (SSD) who underwent cochlear implantation.

DATABASES REVIEWED

PubMed, MEDLINE, Embase, Cochrane Central Register of Controlled Trials, Web of Science, and Scopus databases were searched from January 2008 to September 2021 following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines.

METHODS

Studies reporting spatial hearing, tinnitus, and quality-of-life outcomes in adult cochlear implant (CI) recipients (≥18 yr old) with SSD were evaluated. Study characteristics, demographic data, spatial hearing (speech recognition in noise, sound source localization), tinnitus (severity, loudness), and quality-of-life outcomes were collected.

RESULTS

From an initial search of 1,147 articles, 36 studies that evaluated CI use in 796 unique adults with SSD (51.3 ± 12.4 yr of age at time of implantation) were included. The mean duration of deafness was 6.2 ± 9.6 years. There was evidence of improvement for speech recognition in noise using different target-to-masker spatial configurations, with the largest benefit observed for target-to-masker configurations assessing head shadow (mean, 1.87-6.2 dB signal-to-noise ratio). Sound source localization, quantified as root-mean-squared error, improved with CI use (mean difference [MD], -25.3 degrees; 95% confidence interval [95% CI], -35.9 to -14.6 degrees; p < 0.001). Also, CI users reported a significant reduction in tinnitus severity as measured with the Tinnitus Handicap Inventory (MD, -29.97; 95% CI, -43.9 to -16.1; p < 0.001) and an improvement in spatial hearing abilities as measured with the Spatial, Speech, and Qualities of Hearing questionnaire (MD, 2.3; 95% CI, 1.7 to 2.8; p < 0.001).

CONCLUSIONS

Cochlear implantation and CI use consistently offer improvements in speech recognition in noise, sound source localization, tinnitus, and perceived quality of life in adults with SSD.

Event-Related Potentials of Single-Sided Deaf Cochlear Implant Users: Using a Semantic Oddball Paradigm in Noise

INTRODUCTION

In individuals with single-sided deafness (SSD), who are characterised by profound hearing loss in one ear and normal hearing in the contralateral ear, binaural input is no longer present. A cochlear implant (CI) can restore functional hearing in the profoundly deaf ear, with previous literature demonstrating improvements in speech-in-noise intelligibility with the CI. However, we currently have limited understanding of the neural processes involved (e.g., how the brain integrates the electrical signal produced by the CI with the acoustic signal produced by the normal hearing ear) and how modulation of these processes with a CI contributes to improved speech-in-noise intelligibility. Using a semantic oddball paradigm presented in the presence of background noise, this study aims to investigate how the provision of CI impacts speech-in-noise perception of SSD-CI users.

METHOD

Task performance (reaction time, reaction time variability, target accuracy, subjective listening effort) and high density electroencephalography from twelve SSD-CI participants were recorded, while they completed a semantic acoustic oddball task. Reaction time was defined as the time taken for a participant to press the response button after stimulus onset. All participants completed the oddball task in three different free-field conditions with the speech and noise coming from different speakers. The three tasks were: (1) CI-On in background noise, (2) CI-Off in background noise, and (3) CI-On without background noise (Control). Task performance and electroencephalography data (N2N4 and P3b) were recorded for each condition. Speech in noise and sound localisation ability were also measured.

RESULTS

Reaction time was significantly different between all tasks with CI-On (M [SE] = 809 [39.9] ms) having faster RTs than CI-Off (M [SE] = 845 [39.9] ms) and Control (M [SE] = 785 [39.9] ms) being the fastest condition. The Control condition exhibited significantly shorter N2N4 and P3b area latency compared to the other two conditions. However, despite these differences noticed in RTs and area latency, we observed similar results between all three conditions for N2N4 and P3b difference area.

CONCLUSION

The inconsistency between the behavioural and neural results suggests that EEG may not be a reliable measure of cognitive effort. This rationale is further supported by different explanations used in past studies to explain N2N4 and P3b effects. Future studies should look to alternative measures of auditory processing (e.g., pupillometry) to gain a deeper understanding of the underlying auditory processes that facilitate speech-in-noise intelligibility.

A cortical biomarker of audibility and processing efficacy in children with single-sided deafness using a cochlear implant

The goals of the current study were to evaluate audibility and cortical speech processing, and to provide insight into binaural processing in children with single-sided deafness (CHwSSD) using a cochlear implant (CI). The P1 potential to acoustically-presented speech stimuli (/m/, /g/, /t/) was recorded during monaural [Normal hearing (NH), CI], and bilateral (BIL, NH + CI) listening conditions within a clinical setting in 22 CHwSSD (mean age at CI/testing 4.7, 5.7 years). Robust P1 potentials were elicited in all children in the NH and BIL conditions. In the CI condition: (1) P1 prevalence was reduced yet was elicited in all but one child to at least one stimulus; (2) P1 latency was prolonged and amplitude was reduced, consequently leading to absence of binaural processing manifestations; (3) Correlation between P1 latency and age at CI/testing was weak and not significant; (4) P1 prevalence for /m/ was reduced and associated with CI manufacturer and duration of CI use. Results indicate that recording CAEPs to speech stimuli in clinical settings is feasible and valuable for the management of CHwSSD. While CAEPs provided evidence for effective audibility, a substantial mismatch in timing and synchrony of early-stage cortical processing between the CI and NH ear remains a barrier for the development of binaural interaction components.

Auditory cortical plasticity after cochlear implantation in asymmetric hearing loss is related to spatial hearing: a PET H215O study

In asymmetric hearing loss (AHL), the normal pattern of contralateral hemispheric dominance for monaural stimulation is modified, with a shift towards the hemisphere ipsilateral to the better ear. The extent of this shift has been shown to relate to sound localization deficits. In this study, we examined whether cochlear implantation to treat postlingual AHL can restore the normal functional pattern of auditory cortical activity and whether this relates to improved sound localization. The auditory cortical activity was found to be lower in the AHL cochlear implanted (AHL-CI) participants. A cortical asymmetry index was calculated and showed that a normal contralateral dominance was restored in the AHL-CI patients for the nonimplanted ear, but not for the ear with the cochlear implant. It was found that the contralateral dominance for the nonimplanted ear strongly correlated with sound localization performance (rho = 0.8, P < 0.05). We conclude that the reorganization of binaural mechanisms in AHL-CI subjects reverses the abnormal lateralization pattern induced by the deafness, and that this leads to improved spatial hearing. Our results suggest that cochlear implantation enables the reconstruction of the cortical mechanisms of spatial selectivity needed for sound localization.

Selective attention decoding in bimodal cochlear implant users

The growing group of cochlear implant (CI) users includes subjects with preserved acoustic hearing on the opposite side to the CI. The use of both listening sides results in improved speech perception in comparison to listening with one side alone. However, large variability in the measured benefit is observed. It is possible that this variability is associated with the integration of speech across electric and acoustic stimulation modalities. However, there is a lack of established methods to assess speech integration between electric and acoustic stimulation and consequently to adequately program the devices. Moreover, existing methods do not provide information about the underlying physiological mechanisms of this integration or are based on simple stimuli that are difficult to relate to speech integration. Electroencephalography (EEG) to continuous speech is promising as an objective measure of speech perception, however, its application in CIs is challenging because it is influenced by the electrical artifact introduced by these devices. For this reason, the main goal of this work is to investigate a possible electrophysiological measure of speech integration between electric and acoustic stimulation in bimodal CI users. For this purpose, a selective attention decoding paradigm has been designed and validated in bimodal CI users. The current study included behavioral and electrophysiological measures. The behavioral measure consisted of a speech understanding test, where subjects repeated words to a target speaker in the presence of a competing voice listening with the CI side (CIS) only, with the acoustic side (AS) only or with both listening sides (CIS+AS). Electrophysiological measures included cortical auditory evoked potentials (CAEPs) and selective attention decoding through EEG. CAEPs were recorded to broadband stimuli to confirm the feasibility to record cortical responses with CIS only, AS only, and CIS+AS listening modes. In the selective attention decoding paradigm a co-located target and a competing speech stream were presented to the subjects using the three listening modes (CIS only, AS only, and CIS+AS). The main hypothesis of the current study is that selective attention can be decoded in CI users despite the presence of CI electrical artifact. If selective attention decoding improves combining electric and acoustic stimulation with respect to electric stimulation alone, the hypothesis can be confirmed. No significant difference in behavioral speech understanding performance when listening with CIS+AS and AS only was found, mainly due to the ceiling effect observed with these two listening modes. The main finding of the current study is the possibility to decode selective attention in CI users even if continuous artifact is present. Moreover, an amplitude reduction of the forward transfer response function (TRF) of selective attention decoding was observed when listening with CIS+AS compared to AS only. Further studies to validate selective attention decoding as an electrophysiological measure of electric acoustic speech integration are required.

Single-Sided Deafness: Emotional and Social Handicap, Impact on Health Status and Quality of Life, Functional Hearing, and the Effects of Cochlear Implantation

OBJECTIVE

To evaluate the functional and subjective outcomes in individuals with single-sided deafness (SSD) treated with a cochlear implant (CI).

METHODS

Eighty-one adult CI users with SSD participated in this study. Functional assessments consisted of speech in noise testing and localization. Subjective assessments consisted of the Speech Spatial Quality of Hearing Scale, the Tinnitus Reaction Questionnaire, the Abbreviated Profile of Hearing Aid Benefit questionnaire, the Hearing Handicap Inventory for Adults questionnaire, and the Glasgow Health Status Inventory and the Glasgow Benefit Inventory questionnaires.

RESULTS

SSD has remarkable consequences on quality of life (QoL) and imposes a substantial emotional and social handicap on the individuals. Self-reported QoL improved after CI with tinnitus intrusion significantly reduced as early as 3 months post-CI. A significant improvement was seen in all speech understanding in noise configurations. Localization ability significantly improved with CI on.

CONCLUSION

Our findings demonstrate that SSD reduces social and psychological QoL and imposes a remarkable level of handicap as per general and specific self-assessments tool. CI provided a significant improvement in function including speech understanding in noise and localization ability, as well as improved QoL and reduced tinnitus significantly in both the early and long terms.

The Acoustic Change Complex Compared to Hearing Performance in Unilaterally and Bilaterally Deaf Cochlear Implant Users

OBJECTIVES

Clinical measures evaluating hearing performance in cochlear implant (CI) users depend on attention and linguistic skills, which limits the evaluation of auditory perception in some patients. The acoustic change complex (ACC), a cortical auditory evoked potential to a sound change, might yield useful objective measures to assess hearing performance and could provide insight in cortical auditory processing. The aim of this study is to examine the ACC in response to frequency changes as an objective measure for hearing performance in CI users.

DESIGN

Thirteen bilaterally deaf and six single-sided deaf subjects were included, all having used a unilateral CI for at least 1 year. Speech perception was tested with a consonant-vowel-consonant test (+10 dB signal-to-noise ratio) and a digits-in-noise test. Frequency discrimination thresholds were measured at two reference frequencies, using a 3-interval, 2-alternative forced-choice, adaptive staircase procedure. The two reference frequencies were selected using each participant's frequency allocation table and were centered in the frequency band of an electrode that included 500 or 2000 Hz, corresponding to the apical electrode or the middle electrode, respectively. The ACC was evoked with pure tones of the same two reference frequencies with varying frequency increases: within the frequency band of the middle or the apical electrode (+0.25 electrode step), and steps to the center frequency of the first (+1), second (+2), and third (+3) adjacent electrodes.

RESULTS

Reproducible ACCs were recorded in 17 out of 19 subjects. Most successful recordings were obtained with the largest frequency change (+3 electrode step). Larger frequency changes resulted in shorter N1 latencies and larger N1-P2 amplitudes. In both unilaterally and bilaterally deaf subjects, the N1 latency and N1-P2 amplitude of the CI ears correlated to speech perception as well as frequency discrimination, that is, short latencies and large amplitudes were indicative of better speech perception and better frequency discrimination. No significant differences in ACC latencies or amplitudes were found between the CI ears of the unilaterally and bilaterally deaf subjects, but the CI ears of the unilaterally deaf subjects showed substantially longer latencies and smaller amplitudes than their contralateral normal-hearing ears.

CONCLUSIONS

The ACC latency and amplitude evoked by tone frequency changes correlate well to frequency discrimination and speech perception capabilities of CI users. For patients unable to reliably perform behavioral tasks, the ACC could be of added value in assessing hearing performance.

Single-Sided Deafness: Using Cortical Auditory Evoked Potential to Improve Cochlear Implant Fitting

OBJECTIVE

To investigate if acoustic cortical auditory evoked potential (aCAEP) measures can be used to verify the cochlear implant (CI) map and consequently improve auditory outcomes in adults with single-sided deafness (SSD).

DESIGN

aCAEPs were measured in SSD-CI recipients using speech tokens /m/, /g/, /t/, and /s/. If aCAEP responses were present for all speech tokens at the outset, no map adjustments were implemented. If aCAEP responses were absent for one or more tokens, the map was adjusted until aCAEPs were observed for all four tokens. Speech in noise testing using BKB-SiN was performed before and after aCAEP recording. The results of the speech testing results at presurgery, 6, 12, and 24 months post-CI were also analyzed.

RESULTS

Sixty-seven CI users with SSD participated in this study. All CIs had been mapped according to the conventional subjective loudness perception method. Twenty-three SSD-CI users exhibited an aCAEP response for all four speech tokens and were therefore considered optimized at outset. Forty-four participants lacked an aCAEP response from at least one speech token and had their most comfortable levels adjusted accordingly. Of these, map adjustments allowed aCAEPs to be elicited for all four speech tokens in 23 individuals. Speech in noise testing significantly improved pre- to post-aCAEP-based adjustment.

CONCLUSION

aCAEP recordings were successfully used to verify CI mapping and improve resultant speech outcomes in SSD-CI users.

(Even Off-Label) Cochlear Implantation in Single-Sided Deafness and Asymmetric Hearing Loss Results in Measurable Objective and Subjective Benefit

OBJECTIVE

To quantify objective and subjective outcomes in cochlear implant (CI) recipients with asymmetric hearing loss, including single-sided deafness (SSD) whose candidacy was determined on an ear-specific basis when word recognition was 50% or less.

STUDY DESIGN

Retrospective case review.

SETTING

Tertiary referral center.

BACKGROUND

The effectiveness of CI in cases of SSD and asymmetric hearing loss (AHL) has been described in terms of tinnitus suppression, improved speech recognition in quiet and noise, enhanced localization ability, and improved quality of life. However, CI is not yet routinely offered as a top option or standard of care for these individuals. Recent Food and Drug Administration (FDA) labeling limits aided word recognition in the ear to be implanted to only 5% in cases of AHL/SSD, which is significantly poorer than 40 to 50%, which is often referenced in cases of bilateral hearing loss. Anecdotal experience suggests that patients with much better preoperative word recognition than 5% can benefit from CI.

METHODS

We conducted a retrospective chart review of all adult CI candidates, with one ear exhibiting consonant-nucleus-consonant (CNC) word recognition scores at least 50% and one ear not meeting CI candidacy (i.e., CNC word recognition >50%). Outcome variables of interest included word and sentence recognition and subjective handicap questionnaires (hearing, tinnitus, dizziness) and the Speech Spatial Qualities questionnaire.

RESULTS

Statistically and clinically significant improvement in speech understanding (word, sentence, sentence in noise) was noted for both the SSD and AHL groups in the implanted ear. There were statistically and clinically significant subjective improvements noted for both groups on the Hearing Handicap Inventory, the Tinnitus Handicap Inventory, and the Speech Spatial Qualities questionnaire by 1 month after activation. There were no significant differences between the AHL and SSD groups on either objective or subjective measures of the implanted ear. Individual word understanding improved for the majority of recipients across both groups and is not dependent on meeting the FDA criteria of less than 5%.

CONCLUSIONS

Cochlear implantation is a viable option with measurable objective and perceived benefits for recipients with preoperative aided CNC word scores exceeding current FDA labeling. There is no significant difference between the AHL and SSD groups, suggesting that candidacy and outcome expectations should be set based on the ear to be implanted alone, without regard for the ability of the better hearing ear.

American Cochlear Implant Alliance Task Force Guidelines for Clinical Assessment and Management of Adult Cochlear Implantation for Single-Sided Deafness

The indications for cochlear implantation have expanded to include individuals with profound sensorineural hearing loss in the impaired ear and normal hearing (NH) in the contralateral ear, known as single-sided deafness (SSD). There are additional considerations for the clinical assessment and management of adult cochlear implant candidates and recipients with SSD as compared to conventional cochlear implant candidates with bilateral moderate to profound sensorineural hearing loss. The present report reviews the current evidence relevant to the assessment and management of adults with SSD. A systematic review was also conducted on published studies that investigated outcomes of cochlear implant use on measures of speech recognition in quiet and noise, sound source localization, tinnitus perception, and quality of life for this patient population. Expert consensus and systematic review of the current literature were combined to provide guidance for the clinical assessment and management of adults with SSD.

Sound Localization in Single-Sided Deaf Participants Provided With a Cochlear Implant

Spatial hearing is crucial in real life but deteriorates in participants with severe sensorineural hearing loss or single-sided deafness. This ability can potentially be improved with a unilateral cochlear implant (CI). The present study investigated measures of sound localization in participants with single-sided deafness provided with a CI. Sound localization was measured separately at eight loudspeaker positions (4°, 30°, 60°, and 90°) on the CI side and on the normal-hearing side. Low- and high-frequency noise bursts were used in the tests to investigate possible differences in the processing of interaural time and level differences. Data were compared to normal-hearing adults aged between 20 and 83. In addition, the benefit of the CI in speech understanding in noise was compared to the localization ability. Fifteen out of 18 participants were able to localize signals on the CI side and on the normal-hearing side, although performance was highly variable across participants. Three participants always pointed to the normal-hearing side, irrespective of the location of the signal. The comparison with control data showed that participants had particular difficulties localizing sounds at frontal locations and on the CI side. In contrast to most previous results, participants were able to localize low-frequency signals, although they localized high-frequency signals more accurately. Speech understanding in noise was better with the CI compared to testing without CI, but only at a position where the CI also improved sound localization. Our data suggest that a CI can, to a large extent, restore localization in participants with single-sided deafness. Difficulties may remain at frontal locations and on the CI side. However, speech understanding in noise improves when wearing the CI. The treatment with a CI in these participants might provide real-world benefits, such as improved orientation in traffic and speech understanding in difficult listening situations.

CI in single-sided deafness

The cochlear implant (CI) as a treatment option for single-sided deafness (SSD) started with a clinical study looking in to the influence of cochlear implantation with a MED-EL device on incapacitating unilateral tinnitus in SSD. The study began in 2003 and was conducted by P. Van de Heyning and his team in Antwerp, Belgium. The first CI in SSD without tinnitus in Germany was implanted by J. Mueller and R. Jacob in Koblenz in 2005. Translational research activities took place since then to evaluate the CI as a treatment option for SSD not only in adults but also in children. They assessed the hearing performance of SSD patients implanted with CI, importance of long electrode arrays in SSD patients, degree of acceptance of CI by SSD children, importance of early CI implantation in SSD children in developing language skills, music enjoyment by hearing with two ears and evidence on spiral ganglion cell body distribution. In 2013, MED-EL was the first CI manufacturer to receive the CE mark for the indication of SSD and asymmetric hearing loss (AHL) in adults and children. In 2019, MED-EL was the first CI manufacturer to get its CI device approved for patients over the age of five with SSD and AHL, by the FDA in the USA. This article covers the milestones of translational research from the first concept to the widespread clinical use of CI in SSD.

Cochlear implants in single-sided deaf recipients: Near normal higher-order processing

OBJECTIVE

Single-sided deafness (SSD) is a condition where an individual has a severe to profound sensorineural hearing loss in one ear and normal hearing on the contralateral side. The use of cochlear implants in individuals with SSD leads to functional improvements in hearing. However, it is relatively unclear how sounds incoming via the cochlear implant (independent of the hearing ear) are processed and interpreted by higher-order processes in the brain.

METHODS

Scalp electroencephalography and auditory event-related potentials were recorded monaurally from nine experienced single sided cochlear implant users. Speech-in-noise and localisation tests were used to measure functional changes in hearing.

RESULTS

cochlear implant use was associated with improvement in speech-in-noise and localisation tests (compared to cochlear implant off). Significant N2 and P3b effects were observed in both cochlear implant and normal hearing ear conditions, with similar waveform morphology and scalp distribution across conditions. Delayed response times and a reduced N2 (but not P3b) effect was measured in the CI condition.

CONCLUSION

The brain is capable of using processes similar to those in normal hearing to discriminate sounds presented to the cochlear implant. There was evidence of processing difficulty in the cochlear implant condition which could be due to the relatively degraded signals produced by the cochlear implant compared to the normal hearing ear.

SIGNIFICANCE

Understanding how the brain processes sound provided by a cochlear implant highlights how cortical responses can be used to guide implantation candidacy guidelines and influence rehabilitation recommendations.