Bimodal Listeners Research Articles

Effectiveness and efficiency of a dedicated bimodal fitting formula.

The population of unilateral cochlear implant (CI) users with aidable residual hearing in the contralateral ear is continuously growing. Aiding the contralateral ear with a hearing aid has been shown to provide substantial benefit regarding speech intelligibility in quiet and in noise, sound quality, localization ability and listening effort. In this study, a dedicated hearing aid with the accompanying fitting prescription, tailored to the needs of bimodal listeners was evaluated in nine bimodal CI users. Speech intelligibility scores in noise revealed on-par performance of the dedicated bimodal fitting compared to the clinical standard prescription. 78% of the bimodal CI users preferred the dedicated bimodal fitting over the clinical standard. The minimal subject-specific finetuning effort required during the dedicated bimodal fitting process emphasizes the clinical efficiency.

Bimodal Hearing or Bilateral Cochlear Implants? Ask the Patient.

The objectives of this study were to assess the effectiveness of various measures of speech understanding in distinguishing performance differences between adult bimodal and bilateral cochlear implant (CI) recipients and to provide a preliminary evidence-based tool guiding clinical decisions regarding bilateral CI candidacy. This study used a multiple-baseline, cross-sectional design investigating speech recognition performance for 85 experienced adult CI recipients (49 bimodal, 36 bilateral). Speech recognition was assessed in a standard clinical test environment with a single loudspeaker using the minimum speech test battery for adult CI recipients as well as with an R-SPACE 8-loudspeaker, sound-simulation system. All participants were tested in three listening conditions for each measure including each ear alone as well as in the bilateral/bimodal condition. In addition, we asked each bimodal listener to provide a yes/no answer to the question, "Do you think you need a second CI?" This study yielded three primary findings: (1) there were no significant differences between bimodal and bilateral CI performance or binaural summation on clinical measures of speech recognition, (2) an adaptive speech recognition task in the R-SPACE system revealed significant differences in performance and binaural summation between bimodal and bilateral CI users, with bilateral CI users achieving significantly better performance and greater summation, and (3) the patient's answer to the question, "Do you think you need a second CI?" held high sensitivity (100% hit rate) for identifying likely bilateral CI candidates and moderately high specificity (77% correct rejection rate) for correctly identifying listeners best suited with a bimodal hearing configuration. Clinics cannot rely on current clinical measures of speech understanding, with a single loudspeaker, to determine bilateral CI candidacy for adult bimodal listeners nor to accurately document bilateral benefit relative to a previous bimodal hearing configuration. Speech recognition in a complex listening environment, such as R-SPACE, is a sensitive and appropriate measure for determining bilateral CI candidacy and also likely for documenting bilateral benefit relative to a previous bimodal configuration. In the absence of an available R-SPACE system, asking the patient whether or not s/he thinks s/he needs a second CI is a highly sensitive measure, which may prove clinically useful.

Musical emotion perception in bimodal patients: Relationship between bimodal benefit and neural representation of temporal fine structure using Rhodes piano stimuli

Combining electric and acoustic hearing across ears allows significant “bimodal hearing” benefit for speech recognition, sound quality, and music perception. The degree of bimodal benefit for speech recognition and musical emotion perception is significantly correlated with neural representation of F0 envelope using the frequency following response (FFR) for a 170-ms /da/ stimulus (D’Onofrio et al., in prep). The purpose of the current study is to examine the relationship between bimodal benefit for musical emotion perception and neural representation of F0 using Rhodes piano stimuli at the following fundamental frequencies: 98 Hz (G2), 262 Hz (C4), and 440 Hz (A4). Our hypotheses are (1) the correlation between bimodal benefit and neural representation of F0 and temporal fine structure will be strengthened via use of a “music” stimulus, compared to the /da/ “speech” stimulus, and (2) bimodal benefit for speech recognition will be better explained via FFR for speech stimuli. Stimuli were presented at 90 dB SPL to the non-implanted ear of bimodal listeners using magnetically shielded insert earphones. Implications regarding the clinical utility of FFR will be discussed, with particular attention given to its use as an objective measure of expected bimodal benefit for speech recognition and musical emotion perception.

Factors Affecting Bimodal Benefit in Pediatric Mandarin-Speaking Chinese Cochlear Implant Users.

While fundamental frequency (F0) cues are important to both lexical tone perception and multitalker segregation, F0 cues are poorly perceived by cochlear implant (CI) users. Adding low-frequency acoustic hearing via a hearing aid in the contralateral ear may improve CI users' F0 perception. For English-speaking CI users, contralateral acoustic hearing has been shown to improve perception of target speech in noise and in competing talkers. For tonal languages such as Mandarin Chinese, F0 information is lexically meaningful. Given competing F0 information from multiple talkers and lexical tones, contralateral acoustic hearing may be especially beneficial for Mandarin-speaking CI users' perception of competing speech. Bimodal benefit (CI+hearing aid - CI-only) was evaluated in 11 pediatric Mandarin-speaking Chinese CI users. In experiment 1, speech recognition thresholds (SRTs) were adaptively measured using a modified coordinated response measure test; subjects were required to correctly identify 2 keywords from among 10 choices in each category. SRTs were measured with CI-only or bimodal listening in the presence of steady state noise (SSN) or competing speech with the same (M+M) or different voice gender (M+F). Unaided thresholds in the non-CI ear and demographic factors were compared with speech performance. In experiment 2, SRTs were adaptively measured in SSN for recognition of 5 keywords, a more difficult listening task than the 2-keyword recognition task in experiment 1. In experiment 1, SRTs were significantly lower for SSN than for competing speech in both the CI-only and bimodal listening conditions. There was no significant difference between CI-only and bimodal listening for SSN and M+F (p > 0.05); SRTs were significantly lower for CI-only than for bimodal listening for M+M (p < 0.05), suggesting bimodal interference. Subjects were able to make use of voice gender differences for bimodal listening (p < 0.05) but not for CI-only listening (p > 0.05). Unaided thresholds in the non-CI ear were positively correlated with bimodal SRTs for M+M (p < 0.006) but not for SSN or M+F. No significant correlations were observed between any demographic variables and SRTs (p > 0.05 in all cases). In experiment 2, SRTs were significantly lower with two than with five keywords (p < 0.05). A significant bimodal benefit was observed only for the 5-keyword condition (p < 0.05). With the CI alone, subjects experienced greater interference with competing speech than with SSN and were unable to use voice gender difference to segregate talkers. For the coordinated response measure task, subjects experienced no bimodal benefit and even bimodal interference when competing talkers were the same voice gender. A bimodal benefit in SSN was observed for the five-keyword condition but not for the two-keyword condition, suggesting that bimodal listening may be more beneficial as the difficulty of the listening task increased. The present data suggest that bimodal benefit may depend on the type of masker and/or the difficulty of the listening task.

Reducing the Device Delay Mismatch Can Improve Sound Localization in Bimodal Cochlear Implant/Hearing-Aid Users.

In users of a cochlear implant (CI) together with a contralateral hearing aid (HA), so-called bimodal listeners, differences in processing latencies between digital HA and CI up to 9 ms constantly superimpose interaural time differences. In the present study, the effect of this device delay mismatch on sound localization accuracy was investigated. For this purpose, localization accuracy in the frontal horizontal plane was measured with the original and minimized device delay mismatch. The reduction was achieved by delaying the CI stimulation according to the delay of the individually worn HA. For this, a portable, programmable, battery-powered delay line based on a ring buffer running on a microcontroller was designed and assembled. After an acclimatization period to the delayed CI stimulation of 1 hr, the nine bimodal study participants showed a highly significant improvement in localization accuracy of 11.6% compared with the everyday situation without the delay line (p < .01). Concluding, delaying CI stimulation to minimize the device delay mismatch seems to be a promising method to increase sound localization accuracy in bimodal listeners.

Spatial Speech-in-Noise Performance in Bimodal and Single-Sided Deaf Cochlear Implant Users.

This study compared spatial speech-in-noise performance in two cochlear implant (CI) patient groups: bimodal listeners, who use a hearing aid contralaterally to support their impaired acoustic hearing, and listeners with contralateral normal hearing, i.e., who were single-sided deaf before implantation. Using a laboratory setting that controls for head movements and that simulates spatial acoustic scenes, speech reception thresholds were measured for frontal speech-in-stationary noise from the front, the left, or the right side. Spatial release from masking (SRM) was then extracted from speech reception thresholds for monaural and binaural listening. SRM was found to be significantly lower in bimodal CI than in CI single-sided deaf listeners. Within each listener group, the SRM extracted from monaural listening did not differ from the SRM extracted from binaural listening. In contrast, a normal-hearing control group showed a significant improvement in SRM when using two ears in comparison to one. Neither CI group showed a binaural summation effect; that is, their performance was not improved by using two devices instead of the best monaural device in each spatial scenario. The results confirm a “listening with the better ear” strategy in the two CI patient groups, where patients benefited from using two ears/devices instead of one by selectively attending to the better one. Which one is the better ear, however, depends on the spatial scenario and on the individual configuration of hearing loss.

Aural/Oral Performance of Children with Cochlear Implant under Monaural and Bimodal Listening Conditions: A Parental Evaluation

The study assessed the performance of children with cochlear implant (CI) under monaural and bimodal listening conditions using Parental Evaluation of Aural/Oral Performance of Children (PEACH) questionnaire. A total of 74 children using CI and their parents (either of the biological parent) served as subjects in the present study. The subjects were further divided into two groups based on mode of stimulation used in CI. Group I consisted of children using monaural stimulation in CI i.e. unilateral CI (monaural group). Group II consisted of children using bimodal stimulation in CI i.e. CI in one ear and hearing aid in opposite ear (bimodal group). The results revealed that the subjects of both groups performed significantly poorer under noisy listening conditions compared to quiet listening conditions. The subjects of both the groups performed similar under quiet listening environment. Although, both the groups performed similar under quiet listening condition, the subjects of bimodal group demonstrated significant improvement in aural/oral performance as compared to the subjects of monaural group under noisy listening environment. Thus, it can be inferred that bimodal stimulation in CI provides additional benefits as compared to monaural stimulation in CI especially under noisy listening environments. The findings of the present study complement the existing objective test results which have reported positive outcomes from bimodal stimulation in CI recipients.

How to Optimally Fit a Hearing Aid for Bimodal Cochlear Implant Users: A Systematic Review.

Bimodal hearing has shown to improve speech recognition in quiet and in noise and to improve sound localization compared with unilateral cochlear implant (CI) use alone. Fitting the CI and hearing aid (HA) separately has been described well, but HA fitting procedures for bimodal CI users are not well researched or widely accepted. The aim of the present study was to systematically review the literature on the effect of different HA fitting strategies on auditory performance in bimodal CI users. Original articles, written in English, were identified through systematic searches in Medline (OvidSP), Embase, Web of Science, Scopus, CINAHL, Cochrane, PubMed publisher, and Google Scholar. The quality of the studies was assessed on five aspects: methodologic quality (with the methodological index for nonrandomized studies score), number of subjects, quality of the description of contralateral hearing loss, quality of HA verification, and direct comparison of HA fitting procedures based on auditory performance. A total of 1665 records were retrieved, of which 17 were included for systematical reviews. Critical appraisal led to three high-quality studies, 10 medium-quality studies, and four low-quality studies. The results of the studies were structured according to four topics: frequency response, frequency translation/transposition, dynamic range compression, and loudness. In general, a bimodal benefit was found in most studies, using various strategies for the HA fitting. Using a standard prescription rule such as National Acoustics Laboratory formula-non-linear 1, National Acoustics Laboratory formula-non-linear 2, or desired sensation level is a good starting point in children and adults. Although a bimodal benefit was found in most studies, there is no clear evidence how certain choices in HA fitting contribute to optimal bimodal performance. A generally accepted HA prescription rule is an essential part of most fitting procedures used in the studies. Current evidence suggests that frequency lowering or transposition is not beneficial. Individual fine tuning based on loudness or general preference is often applied, but its additional value for auditory performance should be investigated more thoroughly. Good quality comparative studies are needed to further develop evidence-based fitting procedures in case of bimodal listening.

Temporal Fine Structure Processing, Pitch, and Speech Perception in Adult Cochlear Implant Recipients.

The aim of the study was to investigate the link between temporal fine structure (TFS) processing, pitch, and speech perception performance in adult cochlear implant (CI) recipients, including bimodal listeners who may benefit better low-frequency (LF) temporal coding in the contralateral ear. The study participants were 43 adult CI recipients (23 unilateral, 6 bilateral, and 14 bimodal listeners). Two new LF pitch perception tests-harmonic intonation (HI) and disharmonic intonation (DI)-were used to evaluate TFS sensitivity. HI and DI were designed to estimate a difference limen for discrimination of tone changes based on harmonic or inharmonic pitch glides. Speech perception was assessed using the newly developed Italian Sentence Test with Adaptive Randomized Roving level (STARR) test where sentences relevant to everyday contexts were presented at low, medium, and high levels in a fluctuating background noise to estimate a speech reception threshold (SRT). Although TFS and STARR performances in the majority of CI recipients were much poorer than those of hearing people reported in the literature, a considerable intersubject variability was observed. For CI listeners, median just noticeable differences were 27.0 and 147.0 Hz for HI and DI, respectively. HI outcomes were significantly better than those for DI. Median STARR score was 14.8 dB. Better performers with speech reception thresholds less than 20 dB had a median score of 8.6 dB. A significant effect of age was observed for both HI/DI tests, suggesting that TFS sensitivity tended to worsen with increasing age. CI pure-tone thresholds and duration of profound deafness were significantly correlated with STARR performance. Bimodal users showed significantly better TFS and STARR performance for bimodal listening than for their CI-only condition. Median bimodal gains were 33.0 Hz for the HI test and 95.0 Hz for the DI test. DI outcomes in bimodal users revealed a significant correlation with unaided hearing thresholds for octave frequencies lower than 1000 Hz. Median STARR scores were 17.3 versus 8.1 dB for CI only and bimodal listening, respectively. STARR performance was significantly correlated with HI findings for CI listeners and with those of DI for bimodal listeners. LF pitch perception was found to be abnormal in the majority of adult CI recipients, confirming poor TFS processing of CIs. Similarly, the STARR findings reflected a common performance deterioration with the HI/DI tests, suggesting the cause probably being a lack of access to TFS information. Contralateral hearing aid users obtained a remarkable bimodal benefit for all tests. Such results highlighted the importance of TFS cues for challenging speech perception and the relevance to everyday listening conditions. HI/DI and STARR tests show promise for gaining insights into how TFS and speech perception are being limited and may guide the customization of CI program parameters and support the fine tuning of bimodal listening.

The Effect of Binaural Beamforming Technology on Speech Intelligibility in Bimodal Cochlear Implant Recipients

Although the benefit of bimodal listening in cochlear implant users has been agreed on, speech comprehension remains a challenge in acoustically complex real-life environments due to reverberation and disturbing background noises. One way to additionally improve bimodal auditory performance is the use of directional microphones. The objective of this study was to investigate the effect of a binaural beamformer for bimodal cochlear implant (CI) users. This prospective study measured speech reception thresholds (SRT) in noise in a repeated-measures design that varied in listening modality for static and dynamic listening conditions. A significant improvement in SRT of 4.7 dB was found with the binaural beamformer switched on in the bimodal static listening condition. No significant improvement was found in the dynamic listening condition. We conclude that there is a clear additional advantage of the binaural beamformer in bimodal CI users for predictable/static listening conditions with frontal target speech and spatially separated noise sources.

Comparison between adaptive and adjustment procedures for binaural loudness balancing

Binaural loudness balancing is performed in research and clinical practice when fitting bilateral hearing devices, and is particularly important for bimodal listeners, who have a bilateral combination of a hearing aid and a cochlear implant. In this study, two psychophysical binaural loudness balancing procedures were compared. Two experiments were carried out. In the first experiment, the effect of procedure (adaptive or adjustment) on the balanced loudness levels was investigated using noise band stimuli, of which some had a frequency shift to simulate bimodal hearing. In the second experiment, the adjustment procedure was extended. The effect of the starting level of the adjustment procedure was investigated and the two procedures were again compared for different reference levels and carrier frequencies. Fourteen normal hearing volunteers participated in the first experiment, and 38 in the second experiment. Although the final averaged loudness balanced levels of both procedures were similar, the adjustment procedure yielded smaller standard deviations across four test sessions. The results of experiment 2 demonstrated that in order to avoid bias, the adjustment procedure should be conducted twice, once starting from below and once from above the expected balanced loudness level.

Speech Understanding in Noise for Adults With Cochlear Implants: Effects of Hearing Configuration, Source Location Certainty, and Head Movement.

The primary purpose of this study was to assess speech understanding in quiet and in diffuse noise for adult cochlear implant (CI) recipients utilizing bimodal hearing or bilateral CIs. Our primary hypothesis was that bilateral CI recipients would demonstrate less effect of source azimuth in the bilateral CI condition due to symmetric interaural head shadow. Sentence recognition was assessed for adult bilateral (n = 25) CI users and bimodal listeners (n = 12) in three conditions: (1) source location certainty regarding fixed target azimuth, (2) source location uncertainty regarding roving target azimuth, and (3) Condition 2 repeated, allowing listeners to turn their heads, as needed. (a) Bilateral CI users exhibited relatively similar performance regardless of source azimuth in the bilateral CI condition; (b) bimodal listeners exhibited higher performance for speech directed to the better hearing ear even in the bimodal condition; (c) the unilateral, better ear condition yielded higher performance for speech presented to the better ear versus speech to the front or to the poorer ear; (d) source location certainty did not affect speech understanding performance; and (e) head turns did not improve performance. The results confirmed our hypothesis that bilateral CI users exhibited less effect of source azimuth than bimodal listeners. That is, they exhibited similar performance for speech recognition irrespective of source azimuth, whereas bimodal listeners exhibited significantly poorer performance with speech originating from the poorer hearing ear (typically the nonimplanted ear). Bilateral CI users overcame ear and source location effects observed for the bimodal listeners. Bilateral CI users have access to head shadow on both sides, whereas bimodal listeners generally have interaural asymmetry in both speech understanding and audible bandwidth limiting the head shadow benefit obtained from the poorer ear (generally the nonimplanted ear). In summary, we found that, in conditions with source location uncertainty and increased ecological validity, bilateral CI performance was superior to bimodal listening.

Real-time loudness normalisation with combined cochlear implant and hearing aid stimulation.

BackgroundPeople who use a cochlear implant together with a contralateral hearing aid—so-called bimodal listeners—have poor localisation abilities and sounds are often not balanced in loudness across ears. In order to address the latter, a loudness balancing algorithm was created, which equalises the loudness growth functions for the two ears. The algorithm uses loudness models in order to continuously adjust the two signals to loudness targets. Previous tests demonstrated improved binaural balance, improved localisation, and better speech intelligibility in quiet for soft phonemes. In those studies, however, all stimuli were preprocessed so spontaneous head movements and individual head-related transfer functions were not taken into account. Furthermore, the hearing aid processing was linear.Study designIn the present study, we simplified the acoustical loudness model and implemented the algorithm in a real-time system. We tested bimodal listeners on speech perception and on sound localisation, both in normal loudness growth configuration and in a configuration with a modified loudness growth function. We also used linear and compressive hearing aids.ResultsThe comparison between the original acoustical loudness model and the new simplified model showed loudness differences below 3% for almost all tested speech-like stimuli and levels. We found no effect of balancing the loudness growth across ears for speech perception ability in quiet and in noise. We found some small improvements in localisation performance. Further investigation with a larger sample size is required.

Bilateral Cochlear Implantation Versus Bimodal Hearing in Patients With Functional Residual Hearing: A Within-subjects Comparison of Audiologic Performance and Quality of Life

Evaluate performance and quality of life changes after sequential bilateral cochlear implantation in patients with preoperative residual hearing functioning in a bimodal hearing configuration. Retrospective analysis using within-subjects repeated measures design. Tertiary otologic center. Twenty-two adult patients with bilateral sensorineural hearing loss who used bimodal hearing before second cochlear implant (CI) meeting the following criteria: 1) preoperative residual hearing (≤80 dB HL at 250 Hz) in the ear to be implanted, 2) implantation with current CI technology (2013-2016), 3) consonant-nucleus-consonant (CNC) speech recognition testing in the bimodal condition preoperatively and bilateral CI condition postoperatively. Cochlear implantation. CNC and AzBio sentence scores in quiet and noise (+5 SNR). Subjective measures of communication difficulty and sound quality were also administered. Twenty-two patients (mean 64 yr, 68% men) were included. At an average follow-up of 11.8 months, CNC scores in the bilateral CI condition (mean 63%, standard deviation [SD] = 22) were significantly better than preoperative bimodal scores with repeated measures analysis (mean 55%, SD = 22) (p = 0.03). AzBio scores in quiet were also higher with bilateral CI (mean 76%, SD = 24) compared with bimodal listening (mean 69%, SD = 29) (p = 0.0007). Global abbreviated profile of hearing aid benefit (APHAB) and overall speech, spatial, and qualities of hearing (SSQ) scores exhibited significant improvement following bilateral implantation (p = 0.006 for both analyses). For patients using a bimodal hearing configuration with substantial residual hearing in the non-CI ear, bilateral cochlear implantation yields improved audiologic performance and better subjective quality of life, irrespective of the ability to preserve acoustic hearing during the second sided implantation.

Head shadow enhancement with low-frequency beamforming improves sound localization and speech perception for simulated bimodal listeners

Many hearing-impaired listeners struggle to localize sounds due to poor availability of binaural cues. Listeners with a cochlear implant and a contralateral hearing aid – so-called bimodal listeners – are amongst the worst performers, as both interaural time and level differences are poorly transmitted. We present a new method to enhance head shadow in the low frequencies. Head shadow enhancement is achieved with a fixed beamformer with contralateral attenuation in each ear. The method results in interaural level differences which vary monotonically with angle. It also improves low-frequency signal-to-noise ratios in conditions with spatially separated speech and noise. We validated the method in two experiments with acoustic simulations of bimodal listening. In the localization experiment, performance improved from 50.5∘ to 26.8∘ root-mean-square error compared with standard omni-directional microphones. In the speech-in-noise experiment, speech was presented from the frontal direction. Speech reception thresholds improved by 15.7 dB SNR when the noise was presented from the cochlear implant side, improved by 7.6 dB SNR when the noise was presented from the hearing aid side, and was not affected when noise was presented from all directions. Apart from bimodal listeners, the method might also be promising for bilateral cochlear implant or hearing aid users. Its low computational complexity makes the method suitable for application in current clinical devices.

Musical emotion recognition in bimodal patients

Several cues are used to convey musical emotion, the two primary being musical mode and musical tempo. Specifically, major and minor modes are regarded as having positive and negative valence, respectively, and songs at fast tempi (i.e., quarter note = 92-196, Gosselin et al. (2005); quarter note = 80-255, Peretz et al. (1998)) are associated with more positive valence compared to songs at slow tempi (i.e., quarter note = 40-60, Gosselin et al. (2005); quarter note = 20-100, Peretz et al. (1998)). Caldwell et al. (2015) demonstrated that CI users relied on tempo (fast vs. slow) with little regard for mode (major vs. minor) when interpreting musical emotion, a finding consistent with spectral cues being poorly represented in CI users. The current study is an extension of Caldwell et al. (2015) examining how mode and tempo cues impact musical emotion recognition in bimodal listeners. Our primary hypothesis is that, unlike CI only users, bimodal listeners—with access to F0 and fine structure—will utilize both mode and tempo cues in a manner similar to normal-hearing listeners. Our secondary hypothesis is that low-frequency spectral resolution in the contralateral ear (via tuning curves and spectral modulation detection) will be significantly correlated with degree of bimodal benefit for musical emotion perception.

Cortical plasticity with bimodal hearing in children with asymmetric hearing loss

This longitudinal study aimed to identify auditory plasticity promoted by a cochlear implant in children with asymmetric hearing loss. Participants included 10 children who experienced (mean ± SD) 3.1 ± 3.6 years of asymmetric hearing (difference of 47.2 ± 47.6 dB) before receiving an implant at age 8.7 ± 5.1 years. Multi-channel electroencephalography was measured at initial implant use (5.8 ± 3.2 days) and after 10.2 ± 4.1 months in each child. Monaurally presented stimuli consisted of 36 ms trains of 9 acoustic clicks/biphasic electric pulses at a rate of 250 Hz, repeated at 1 Hz. The time-restricted artifact and coherent source suppression (TRACS) beamformer was used to locate sources underlying peak amplitudes of cortical responses. Results indicated consistent activity from the non-implanted ear but significant implant-driven changes to the auditory cortices. Initially, the newly implanted ear evoked activity which strongly lateralized to the ipsilateral auditory cortex and contributed to a significant aural preference for implant stimulation in children with limited acoustic experience pre-implantation. Cochlear implant use reversed these abnormalities, but the resolution was limited in children with longer periods of asymmetric hearing. These findings suggest that early implantation of children with asymmetric hearing rapidly restores hemispheric representations of bilateral auditory input in the auditory cortex. Most recorded changes were isolated to pathways stimulated by the cochlear implant, potentially reflecting an abnormal independence of the bilateral pathways with possible consequences for binaural integration in these bimodal listeners.

The Benefits of Residual Hair Cell Function for Speech and Music Perception in Pediatric Bimodal Cochlear Implant Listeners.

Objective The aim of this study was to investigate the benefits of residual hair cell function for speech and music perception in bimodal pediatric Mandarin-speaking cochlear implant (CI) listeners. Design Speech and music performance was measured in 35 Mandarin-speaking pediatric CI users for unilateral (CI-only) and bimodal listening. Mandarin speech perception was measured for vowels, consonants, lexical tones, and sentences in quiet. Music perception was measured for melodic contour identification (MCI). Results Combined electric and acoustic hearing significantly improved MCI and Mandarin tone recognition performance, relative to CI-only performance. For MCI, performance was significantly better with bimodal listening for all semitone spacing conditions (p < 0.05 in all cases). For tone recognition, bimodal performance was significantly better only for tone 2 (rising; p < 0.05). There were no significant differences between CI-only and CI + HA for vowel, consonant, or sentence recognition. Conclusions The results suggest that combined electric and acoustic hearing can significantly improve perception of music and Mandarin tones in pediatric Mandarin-speaking CI patients. Music and lexical tone perception depends strongly on pitch perception, and the contralateral acoustic hearing coming from residual hair cell function provided pitch cues that are generally not well preserved in electric hearing.

Objective Binaural Loudness Balancing Based on 40-Hz Auditory Steady-State Responses. Part II: Asymmetric and Bimodal Hearing.

In Part I, we investigated 40-Hz auditory steady-state response (ASSR) amplitudes for the use of objective loudness balancing across the ears for normal-hearing participants and found median across-ear ratios in ASSR amplitudes close to 1. In this part, we further investigated whether the ASSR can be used to estimate binaural loudness balance for listeners with asymmetric hearing, for whom binaural loudness balancing is of particular interest. We tested participants with asymmetric hearing and participants with bimodal hearing, who hear with electrical stimulation through a cochlear implant (CI) in one ear and with acoustical stimulation in the other ear. Behavioral loudness balancing was performed at different percentages of the dynamic range. Acoustical carrier frequencies were 500, 1000, or 2000 Hz, and CI channels were stimulated in apical or middle regions in the cochlea. For both groups, the ASSR amplitudes at balanced loudness levels were similar for the two ears, with median ratios between left and right ear stimulation close to 1. However, individual variability was observed. For participants with asymmetric hearing loss, the difference between the behavioral balanced levels and the ASSR-predicted balanced levels was smaller than 10 dB in 50% and 56% of cases, for 500 Hz and 2000 Hz, respectively. For bimodal listeners, these percentages were 89% and 60%. Apical CI channels yielded significantly better results (median difference near 0 dB) than middle CI channels, which had a median difference of −7.25 dB.

Bilateral cochlear implantation or bimodal listening in the paediatric population: Retrospective analysis of decisive criteria

IntroductionIn children with bilateral severe to profound hearing loss, bilateral hearing can be achieved by either bimodal stimulation (CIHA) or bilateral cochlear implantation (BICI). The aim of this study was to analyse the audiologic test protocol that is currently applied to make decisions regarding the bilateral hearing modality in the paediatric population. MethodsPre- and postoperative audiologic test results of 21 CIHA, 19 sequential BICI and 12 simultaneous BICI children were examined retrospectively. ResultsDeciding between either simultaneous BICI or unilateral implantation was mainly based on the infant's preoperative Auditory Brainstem Response thresholds. Evolution from CIHA to sequential BICI was mainly based on the audiometric test results in the contralateral (hearing aid) ear after unilateral cochlear implantation. Preoperative audiometric thresholds in the hearing aid ear were significantly better in CIHA versus sequential BICI children (p < 0.001 and p = 0.001 in unaided and aided condition, respectively). Decisive values obtained in the hearing aid ear in favour of BICI were: An average hearing threshold measured at 0.5, 1, 2 and 4 kHz of at least 93 dB HL without, and at least 52 dB HL with hearing aid together with a 40% aided speech recognition score and a 70% aided score on the phoneme discrimination subtest of the Auditory Speech Sounds Evaluation test battery. ConclusionsAlthough pure tone audiometry offers no information about bimodal benefit, it remains the most obvious audiometric evaluation in the decision process on the mode of bilateral stimulation in the paediatric population. A theoretical test protocol for adequate evaluation of bimodal benefit in the paediatric population is proposed.