Bilateral Cochlear Implants Use Research Articles

Predictive factors for broad binaural pitch fusion in adults with hearing aids and cochlear implants

Many adults with hearing loss who use hearing aids (HAs) and/or cochlear implants (CIs) have broad binaural pitch fusion, such that sounds with large pitch differences are fused across ears, leading to difficulties separating voices in multi-talker environments. However, there is individual variation. The goal of the current study was to investigate whether auditory experience factors explain this variation in broad binaural fusion. Binaural fusion was measured in adults with various hearing device combinations: 26 bilateral HA, 25 bimodal CI, and 27 bilateral CI users. Fusion ranges were measured by simultaneous, dichotic presentation of reference and comparison stimuli in opposite ears, and varying the comparison stimulus to find the range that fused with the reference stimulus. Factors examined included age at testing, degree of HL, amount of amplification, age of onset of HL, duration of HL without CI, and duration of HA, bimodal CI, and bilateral CI use. Preliminary analyses suggest that broad fusion is correlated with long durations of HA use; further analyses using multivariable models will be described. The findings will indicate how hearing device experience may influence binaural pitch fusion. [Work supported by NIH grant R01 DC013307.]

Effects of bilateral cochlear implants on vocal intensity control

Bilateral Cochlear Implants (BiCIs) can improve many perceptual tasks, including speech perception in noise, when compared to unilateral implantation. However, evidence suggests that BiCI users may perform worse on some vocal tasks, such as F0 production, than when using their better ear alone. This research aimed to determine if this detrimental effect on vocal control with BiCI devices extends to the control of vocal amplitude variations. Ten BiCI users were asked to produce a sustained vowel vocalization using both CIs and one CI separately. Their recordings were analyzed acoustically to determine long-term control of amplitude variations using the Variation of Peak Amplitude (vAm). The preliminary findings showed that using both CIs resulted in less control over vocal intensity for eight participants when compared to using one ear alone. The other two participants either showed no difference between the conditions or had a higher vAm with the unilateral ear than with the bilateral condition. The result suggests that BiCI use might detrimentally affect controlling long-term vocal intensity variation beyond any effects of unilateral CIs. Further investigation is needed to address how the vocal intensity control in BiCI users is affected.

Longitudinal Effects of Simultaneous and Sequential Bilateral Cochlear Implantation on Cortical Auditory-Evoked Potentials Recorded at Cz in a Large Cohort of Children.

Auditory development after bilateral cochlear implantation in children has been measured using source localization of multi-channel late latency responses. It is not clear, however, whether this development can be tracked using a more clinically feasible method of recording from one active recording electrode placed at mid-line center of the head (Cz). In this prospective cohort study, cortical auditory-evoked potential responses (CAEPs) were recorded from Cz referenced to each earlobe (Cz-CAEP) from 222 children with bilateral cochlear implant (CI); 128 (mean ± SD age: 2.78 ± 3.30 years) received both CIs in the same surgery (simultaneous group) and 94 (aged 7.72 ± 4.45 years) received a second CI after 4.21 ± 2.98 years of unilateral CI use. We sought to (1) identify cortical development over the first couple of years of bilateral CI use; (2) measure known asymmetries in auditory development between the CIs; and (3) detect the effects of bilateral rather than unilateral CI use. 4556 Cz-CAEPs were recorded across the cohort over 33.50 ± 7.67 months duration of bilateral CI use. Given concerns related to peak picking, amplitude areas were measured across two response time windows (50 to 199 ms and 200 to 400 ms). Results indicated that small response amplitudes occur at initial CI use and amplitudes increase in the negative or positive direction rapidly over the first months of CI use in both time windows. Asymmetries between Cz-CAEPs evoked by each CI were found in the sequential group and reduced with bilateral CI use, particularly in the first time window; these differences increased with longer inter-implant delay. Bilaterally evoked Cz-CAEPs were larger in amplitude than unilateral responses from either CI in the simultaneous group. In the sequential group, bilateral responses were similar to responses from the first implanted side but increased in relative amplitude with bilateral CI use. The Cz-CAEP measures were not able to predict asymmetries or bilateral benefits in speech perception measures. The Cz-CAEP was able to indicate cortical detection of CI input and showed gross morphological changes with bilateral CI use. Findings indicate Cz-CAEPs can be used to identify gross changes in auditory development in children with bilateral CIs, but they are less sensitive to tracking the remaining abnormalities that are measured by multi-channel CAEPs and speech perception testing.

Effects of Sequential Bilateral Cochlear Implantation in Children: Evidence from Speech-Evoked Cortical Potentials and Tests of Speech Perception

Introduction: Benefits of bilateral cochlear implants (CI) may be compromised by delays to implantation of either ear. This study aimed to evaluate the effects of sequential bilateral CI use in children who received their first CI at young ages, using a clinical set-up. Methods: One-channel cortical auditory evoked potentials and speech perception in quiet and noise were evoked at repeated times (0, 3, 6, 12 months of bilateral CI use) by unilateral and bilateral stimulation in 28 children with early-onset deafness. These children were unilaterally implanted before 3.69 years of age (mean ± SD of 1.98 ± 0.73 years) and received a second CI after 5.13 ± 2.37 years of unilateral CI use. Comparisons between unilaterally evoked responses were used to measure asymmetric function between the ears and comparisons between bilateral responses and each unilateral response were used to measure the bilateral benefit. Results: Chronic bilateral CI promoted changes in cortical auditory responses and speech perception performance; however, large asymmetries were present between the two unilateral responses despite ongoing bilateral CI use. Persistent cortical differences between the two sides at 1 year of bilateral stimulation were predicted by increasing age at the first surgery and inter-implant delay. Larger asymmetries in speech perception occurred with longer inter-implant delays. Bilateral responses were more similar to the unilateral responses from the first rather than the second CI. Conclusion: These findings are consistent with the development of the aural preference syndrome and reinforce the importance of providing bilateral CIs simultaneously or sequentially with very short delays.

Factors affecting phoneme discrimination in children with sequential bilateral cochlear implants

Objectives To investigate the effects of a number of variables on phoneme discrimination (PD) performance in children with sequential bilateral cochlear implants (SeqBiCIs) and compare PD performance between the 2 implantation sides and between children with bilateral cochlear implants (BiCIs) and their age-matched peers with normal hearing (NH). Design All participants completed the Auditory Speech Sound Evaluation Phoneme Discrimination Test. Study sample The sample included 23 children with SeqBiCIs as the study group and 23 with NH as the control group. Results A significant difference was found between the scores of the two groups under the CI1 and CI2 conditions (p = 0.001), CI1 and BiCI conditions (p = 0.002), and CI2 and BiCI conditions (p = 0.001). PD scores with CI1 significantly depend on age at CI1 and duration of bilateral use. PD scores with CI1 were significant predictors of PD performance with CI2. Duration of BiCI use was a significant predictor of PD scores with BiCI. Conclusions The age at CI1 and the duration of bilateral cochlear implant use were found to improve phoneme discrimination performance in children with a sequential bilateral cochlear implant. According to the success of the CI1, it is possible to predict the success of CI2 use.

Late Receipt of a Second Cochlear Implant: Better Late than Never?

The present study explored the incremental benefits of late receipt of a second cochlear implant (CI) by examining various aspects of educational, cognitive and social-emotional functioning among college-age CI users. Secondary analyses were conducted on data from seven studies that had compared deaf students who were active CI users, deaf students who had never used CIs and hearing students; information concerning unilateral or bilateral CI use had been collected but was not analysed previously. The seven studies provided for comparisons on four dozen dimensions including executive function, world knowledge, visual-spatial ability, academic achievement and quality of life. Ages of first/only cochlear implantation did not differ significantly in any of the comparisons, nor did the groups differ significantly on most of the outcome measures across cognitive and social-emotional domains. The findings consistently indicated that while cognitive and social-emotional differences might be apparent between samples of unilateral and bilateral CI users during earlier childhood, they were not evident in this group of CI users who had reached college-age. Limitations of this study related to the nature of the participant samples indicate the need for further research on long-term benefits of bilateral implantation.

Speech Perception, Dichotic Listening, and Ear Advantage in Simultaneous Bilateral Cochlear Implanted Children

To study the development of dichotic listening, ear advantage, and speech perception in cochlear implant (CI) recipients using five audiometric tests. Prospective cohort analysis. University Hospital. One hundred twenty one participants who received simultaneous bilateral CIs and had at least 12 months of regular bilateral CI use. Age at time of testing ranged from 4 to 18 years with a mean age of 9 years (standard deviation [SD]: 3.0). Mean duration of CI use was 7.073 years (SD: 2.86). Bilateral simultaneous cochlear implantation. Goettinger and Freiburger monosyllabic word test, Hochmair, Schulz and Desoyer sentence (HSM) test in noise and in quiet conditions and the dichotic listening test by Uttenweiler were applied according to the childrens' age. The results were evaluated using a two-sided t test for dependent samples. In all tests applied, we could not show significant differences in performance between left and right CI and therefore could not demonstrate an ear advantage. Dichotic listening was challenging, only one subject produced results required for normal hearing subjects to pass the test. The older the CI recipients get and duration of CI use increases, the more results in all speech perception tests improve. Our results cannot lend further support to the existence of ear advantage in CI recipients. We do not recommend the Uttenweiler dichotic listening test to determine lateralization. Further research to gather more information on dichotic listening and ear advantage in CI recipients is necessary and should use consonant-vowel stimuli as more comparable stimuli.

Pitch Matching Adapts Even for Bilateral Cochlear Implant Users with Relatively Small Initial Pitch Differences Across the Ears.

There is often a mismatch for bilateral cochlear implant (CI) users between the electrodes in the two ears that receive the same frequency allocation and the electrodes that, when stimulated, yield the same pitch. Studies with CI users who have extreme mismatches between the two ears show that adaptation occurs in terms of pitch matching, reducing the difference between which electrodes receive the same frequency allocation and which ones produce the same pitch. The considerable adaptation that occurs for these extreme cases suggests that adaptation should be sufficient to overcome the relatively minor mismatches seen with typical bilateral CI users. However, even those with many years of bilateral CI use continue to demonstrate a mismatch. This may indicate that adaptation only occurs when there are large mismatches. Alternatively, it may indicate that adaptation occurs regardless of the magnitude of the mismatch, but that adaptation is proportional to the magnitude of the mismatch, and thus never fully counters the original mismatch. To investigate this, six bilateral CI users with initial pitch-matching mismatches of less than 3mm completed a pitch-matching task near the time of activation, 6months after activation, and 1year after activation. Despite relatively small initial mismatches, the results indicated that adaptation still occurred.

Bilateral cochlear implantation is regarded as very beneficial: results from a worldwide survey by online questionnaire.

Bilateral cochlear implant (CI) provision is now widely regarded as the most beneficial hearing intervention for acceptable candidates. This study sought to determine if a number of well-regarded hearing professionals at highly reputable clinics shared similar practices and beliefs regarding bilateral CI provision, use, and rehabilitation in children and adults. An 11-question online questionnaire was created and distributed to all 27 clinics in the HEARRING group. Questions 1-5 asked for facts; questions 6-11 asked for opinions. 20 completed questionnaires were returned. All 20 respondents reported that their clinics perform bilateral cochlear implantation in children; 18 do so in adults. Regarding the fact-based questions, bilateral CI provision is more commonly performed and more likely to be reimbursed in children than in adults. Children are also much more likely to be implanted simultaneously than are adults. Regarding the opinion-based questions, respondents gave broadly similar answers. Communication between the CIs and speech coding strategies specifically developed for bilateral CI users were regarded as the two future technologies that would most enhance the benefit of bilateral CI use. Most clinics in the HEARRING group are very familiar with bilateral CI provision and hold similar opinions on its results and benefits. Hopefully the results described herein will lead to a greater acceptance and regular reimbursement of bilateral CI provision, especially in adults.

The Cost-Effectiveness of Bimodal Stimulation Compared to Unilateral and Bilateral Cochlear Implant Use in Adults with Bilateral Severe to Profound Deafness.

An increasing number of severe-profoundly deaf adult unilateral cochlear implant (CI) users receive bimodal stimulation; that is, they use a conventional acoustic hearing aid (HA) in their nonimplanted ear. The combination of electric and contralateral acoustic hearing provides additional benefits to hearing and also to general health-related quality of life compared with unilateral CI use. Bilateral CI is a treatment alternative to both unilateral CI and bimodal stimulation in some healthcare systems. The objective of this study was to conduct an economic evaluation of bimodal stimulation compared with other management options for adults with bilateral severe to profound deafness. The economic evaluation took the form of a cost-utility analysis and compared bimodal stimulation (CI+HA) to two treatment alternatives: unilateral and bilateral CI. The analysis used a public healthcare system perspective based on data from the United Kingdom and the United States. Costs and health benefits were identified for both alternatives and estimated across a patient's lifetime using Markov state transition models. Utilities were based on Health Utilities Index estimates, and health outcomes were expressed in Quality Adjusted Life Years (QALYs). The results were presented using the Incremental Cost-Effectiveness Ratio and the Net Monetary Benefit approach to determine the cost-effectiveness of bimodal stimulation. Probabilistic sensitivity analyses explored the degree of overall uncertainty using Monte Carlo simulation. Deterministic sensitivity analyses and analysis of covariance identified parameters to which the model was most sensitive; that is, whose values had a strong influence on the intervention that was determined to be most cost-effective. A value of information analysis was performed to determine the potential value to be gained from additional research on bimodal stimulation. The base case model showed that bimodal stimulation was the most cost-effective treatment option with a decision certainty of 72 and 67% in the United Kingdom and United States, respectively. Despite producing more QALYs than either unilateral CI or bimodal stimulation, bilateral CI was found not to be cost-effective because it was associated with excessive costs. Compared with unilateral CI, the increased costs of bimodal stimulation were outweighed by the gain in quality of life. Bimodal stimulation was found to cost an extra £174 per person in the United Kingdom ($937 in the US) and yielded an additional 0.114 QALYs compared with unilateral CI, resulting in an Incremental Cost-Effectiveness Ratio of £1521 per QALY gained in the United Kingdom ($8192/QALY in the United States). The most influential variable was the utility gained from the simultaneous use of both devices (CI+HA) compared with Unilateral CI. The value of further research was £4,383,922 at £20,000/QALY ($86,955,460 at $50,000/QALY in the United States). This study provides evidence of the most cost-effective treatment alternative for adults with bilateral severe to profound deafness from publicly funded healthcare perspectives of the United Kingdom and United States. Bimodal stimulation was found to be more cost-effective than unilateral and bilateral CI across a wide range of willingness-to-pay thresholds. If there is scope for future research, conducting interventional designs to obtain utilities for bimodal stimulation compared with unilateral CI would reduce decision uncertainty considerably.

Balancing current levels in children with bilateral cochlear implants using electrophysiological and behavioral measures

Children have benefited from bilateral cochlear implants (CIs) over unilateral CIs despite often missing important periods in bilateral auditory development. This suggests a remarkable perceptual ability by children to “work around” abnormal changes in the auditory pathways. Nonetheless, these children rely primarily on interaural level differences as interaural timing cues are more difficult to access or detect. Mismatched levels provided to the two implants could distort interaural level cues thus compromising the benefits of bilateral CI use. We asked whether “balanced” or “centered” perception of bilateral input can be predicted by physiological or behavioral measures. Twenty-four children who had used unilateral CIs for 9.21 ± 2.66 years prior to bilateral implantation participated. “Balanced bilateral levels” were identified by responses occurring with a probability of 50% on the right side of the head and 50% on the left in a two choice lateralization task. Loudness judgments of current presented unilaterally by each implant were measured on a continuous visual scale. Maximum wave eV amplitudes were evoked unilaterally by each implant and matched amplitudes were identified. Balanced bilateral levels were predicted within 10 Clinical Units (CU) in 9 of 13 (69%) children using matched wave eV amplitudes. Bilaterally balanced levels were reasonably predicted by similar loudness judgments (<10% difference between CIs) in only 6 of 13 (46%) children. Results indicate that matching amplitudes of physiological responses can produce a balanced perception of bilateral input despite unilateral strengthening of the auditory pathways and can potentially be used clinically to provide a first approximation of balance/centered levels.

Academic Outcomes for School-Aged Children With Severe-Profound Hearing Loss and Early Unilateral and Bilateral Cochlear Implants.

This study sought to (a) determine whether academic outcomes for children who received early cochlear implants (CIs) are age appropriate, (b) determine whether bilateral CI use significantly improves academic outcomes, and (c) identify other factors that are predictive of these outcomes. Forty-four 8-year-old children with severe-profound hearing loss participated in this study. Their academic development in mathematics, oral language, reading, and written language was assessed using a standardized test of academic achievement. (a) Across all academic areas, the proportion of children in the average or above-average ranges was lower than expected for children with normal hearing. The strongest area of performance was written language, and the weakest was mathematics. (b) Children using bilateral CIs achieved significantly higher scores for oral language, math, and written language, after controlling for predictive factors, than did children using unilateral CIs. Younger ages at second CI predicted the largest improvements. (c) High levels of parental involvement and greater time spent by children reading significantly predicted academic success, although other factors were identified. Average academic outcomes for these children were below those of children with normal hearing. Having bilateral CIs at younger ages predicted the best outcomes. Family environment was also important to children's academic performance.

Evidence for a right cochlear implant advantage in simultaneous bilateral cochlear implantation

To compare speech perception performance with right versus left cochlear implants (CIs) in children with bilateral CIs implanted simultaneously. Prospective case series of patients undergoing simultaneous bilateral cochlear implantation. Speech perception performance was tested in 10, right-handed children who received bilateral CIs simultaneously between 11 and 36 months (mean, 21 months), had at least 18 months of bilateral CI use, and were 5.3 years of age during testing. All children exhibited bilateral symmetrical severe-to-profound hearing loss prior to implantation and did not benefit from hearing aids. Speech perception performance was evaluated with the right CI and the left CI by means of an open-set monosyllabic word test in quiet presented at 45 dB HL in a sound field. All children exhibited higher performance with the right CI compared to the left CI. Group mean performance with the right CI was 66.5% compared to 52% with the left CI (P = .002), yielding a 14.5% difference. With increasing duration of bilateral CI use and age at evaluation, the right-left difference increased (r = 0.72, P = .019 and r = 0.74, P = .014, respectively). Current preliminary data indicate that children with bilateral CIs implanted simultaneously exhibit a significant right ear advantage for speech. Similarly to reports on normal-hearing children, right ear preference for speech increased with increasing age and auditory-linguistic experience. Thus, simultaneous bilateral cochlear implantation may lead to normal development of auditory pathways and may be an important contributor to the superior auditory, language, and communication skills reported in children with bilateral versus unilateral CIs.

Factors associated with poor use of sequential bilateral cochlear implants in young people: A preliminary audit of poor users

Six cases of poor sequential bilateral cochlear implant use (partial and complete non-use) were explored through a semi-structured interview, as part of a service evaluation and development audit to improve the quality of a paediatric implant service for sequential users. Themes associated with poor use include: (1) appearance issues, (2) unrealistic expectations of both the benefits and the challenges of adjustment, (3) poor personal motivation for the implant and for engagement in rehabilitation, and (4) dislike of the sound. Feedback from young people highlighted the importance of careful counselling about their expectations of sequential implantation, outcomes and challenges, systemic support and self-directed rehabilitation.

The Effects of Training on Recognition of Musical Instruments by Adults with Cochlear Implants

This study examines the efficiency and effectiveness of three types of training on recognition of musical instruments by adults with cochlear implants (CI). Seventy-one adults with CIs were randomly assigned to one of three training conditions: feedback on response accuracy, feedback-plus (response accuracy plus correct answer), and direct instruction. Each participant completed three training sessions per week over a five-week time period in which they listened to recorded excerpts of eight different musical instruments. Results showed significant pre-to-posttest improvement in music instrument recognition accuracy for all three training conditions (22.9-25.7%, p< 0.0001). Time when tested (week), bilateral CI use, and age were significant predictors of performance. Participants who wore bilateral implants scored significantly higher than participants with unilateral implants at all three time points; hearing aid use was not a significant predictor. These results may have practical implications for numerous types of auditory rehabilitation for persons who use CIs.

Binaural Interactions Develop in the Auditory Brainstem of Children Who Are Deaf: Effects of Place and Level of Bilateral Electrical Stimulation

Bilateral cochlear implants (CIs) might promote development of binaural hearing required to localize sound sources and hear speech in noise for children who are deaf. These hearing skills improve in children implanted bilaterally but remain poorer than normal. We thus questioned whether the deaf and immature human auditory system is able to integrate input delivered from bilateral CIs. Using electrophysiological measures of brainstem activity that include the Binaural Difference (BD), a measure of binaural processing, we showed that a period of unilateral deprivation before bilateral CI use prolonged response latencies but that amplitudes were not significantly affected. Tonotopic organization was retained to some extent as evidenced by an elimination of the BD with large mismatches in place of stimulation between the two CIs. Smaller place mismatches did not affect BD latency or amplitude, indicating that the tonotopic organization of the auditory brainstem is underdeveloped and/or not well used by CI stimulation. Finally, BD amplitudes decreased when the intensity of bilateral stimulation became weighted to one side and this corresponded to a perceptual shift of sound away from midline toward the side of increased intensity. In summary, bilateral CI stimulation is processed by the developing human auditory brainstem leading to perceptual changes in sound location and potentially improving hearing for children who are deaf.

Cortical Function in Children Receiving Bilateral Cochlear Implants Simultaneously or After a Period of Interimplant Delay

Children using bilateral cochlear implants (CIs) develop normal patterns of cortical activity when interimplant delays are minimized. It is not clear whether bilateral CIs can promote normally functioning bilateral auditory pathways in children. Cortical responses were recorded from 64 cephalic sites in 2 normal hearing participants and 8 children with 3 to 4 years of bilateral CI experience (age at first CI, 0.9-4.1 yr; age at second CI, 1.1-9.7 yr; interimplant delay, 0-5.8 yr). Beamformer analyses on the dominant positive peak in CI users and P1 in normal hearers revealed that stimuli delivered from the left side evoked responses lateralized to right auditory cortex in the 2 participants with normal hearing and the 3 children receiving bilateral CIs with minimal interimplant delay at young ages. These 5 participants showed a shift in cortical lateralization away from the right cortical hemisphere when stimuli were moved to the right. In contrast, 4 of 5 children receiving bilateral CIs after longer delays and at older ages showed abnormal ipsilateral parietal activity in response to left stimuli and lateralization to the left cortical hemisphere in response to both right and left stimuli. The fifth child in this group showed abnormal lateralization to the ipsilateral cortex in response to both right and left stimuli. The data suggest that, after 3 to 4 years of bilateral CI use, normal-like patterns of bilateral cortical activity are promoted in children receiving bilateral CI with minimal interimplant delays and young ages but are not present in older children who had longer interimplant delays.

Temporal Stability of Music Perception and Appraisal Scores of Adult Cochlear Implant Recipients

An extensive body of literature indicates that cochlear implants (CIs) are effective in supporting speech perception of persons with severe to profound hearing losses who do not benefit to any great extent from conventional hearing aids. Adult CI recipients tend to show significant improvement in speech perception within 3 mo following implantation as a result of mere experience. Furthermore, CI recipients continue to show modest improvement as long as 5yr postimplantation. In contrast, data taken from single testing protocols of music perception and appraisal indicate that CIs are less than ideal in transmitting important structural features of music, such as pitch, melody, and timbre. However, there is presently little information documenting changes in music perception or appraisal over extended time as a result of mere experience. This study examined two basic questions: (1) Do adult CI recipients show significant improvement in perceptual acuity or appraisal of specific music listening tasks when tested in two consecutive years? (2) If there are tasks for which CI recipients show significant improvement with time, are there particular demographic variables that predict those CI recipients most likely to show improvement with extended CI use? A longitudinal cohort study. Implant recipients return annually for visits to the clinic. The study included 209 adult cochlear implant recipients with at least 9 mo implant experience before their first year measurement. Outcomes were measured on the patient's annual visit in two consecutive years. Paired t-tests were used to test for significant improvement from one year to the next. Those variables demonstrating significant improvement were subjected to regression analyses performed to detect the demographic variables useful in predicting said improvement. There were no significant differences in music perception outcomes as a function of type of device or processing strategy used. Only familiar melody recognition (FMR) and recognition of melody excerpts with lyrics (MERT-L) showed significant improvement from one year to the next. After controlling for the baseline value, hearing aid use, months of use, music listening habits after implantation, and formal musical training in elementary school were significant predictors of FMR improvement. Bilateral CI use, formal musical training in high school and beyond, and a measure of sequential cognitive processing were significant predictors of MERT-L improvement. These adult CI recipients as a result of mere experience demonstrated fairly consistent music perception and appraisal on measures gathered in two consecutive years. Gains made tend to be modest, and can be associated with characteristics such as use of hearing aids, listening experiences, or bilateral use (in the case of lyrics). These results have implications for counseling of CI recipients with regard to realistic expectations and strategies for enhancing music perception and enjoyment.

Abnormal Timing Delays in Auditory Brainstem Responses Evoked by Bilateral Cochlear Implant Use in Children

A period of unilateral implant use before bilateral implantation affects timing of brainstem processes measured by the electrically evoked auditory brainstem response (EABR). EABR latencies decrease with unilateral implant use potentially disrupting binaural timing cues important in auditory brainstem processing of bilateral input. EABRs were evoked by electrical pulses from the left, right, and both implants simultaneously in 3 groups of children. All were initially implanted at ages younger than 3 years and had the following: 1) a long delay (>2 yr [n = 16]), 2) a short delay (<1 yr [n = 15]), or 3) no delay (n = 15) between left and right ear implantation. Responses were recorded on the first day of bilateral implant use and 3 and 9 months thereafter. Relative to responses evoked in the experienced ear, the naive ear showed prolonged latency in both the EABR peaks and the binaural difference response. After 3 and 9 months of bilateral implant use, the relative prolongation decreased in the long and short delay groups, but significant differences persisted in the former. No clear differences in latencies evoked by the left versus right implant were found at any time point in children receiving bilateral implants simultaneously. Results suggest potential disruptions to binaural brainstem processing based on timing cues in children receiving a second cochlear implant after more than 2 years of unilateral implant use that persist through at least the first 9 months of bilateral implant use.