Sound localising ability in children with bilateral sequential cochlear implants

Selection of the optimal first ear for sequential bilateral cochlear implantation in children

OBJECTIVES

When there is a difference in hearing on both ears, where to perform the first cochlear implantation (CI) becomes an important issue. The purpose of the study was to evaluate which ear should be chosen for the first implantation in sequential bilateral CI with a long inter-implant period.

METHODS

The study population consisted of 34 severe-to-profound sensorineural hearing loss pediatrics with the inter-implant period of ≥3 years between the first CI (CI-1) and the second CI (CI-2) before the age of 19 (mean of inter-implant period: 7.1-year). The patients were classified into Group A (CI-1 was performed on the ear with better hearing), Group B (CI-1 on the ear with worse hearing), or Group C (symmetrical hearing in both ears). Speech intelligibility test results were compared between the groups.

RESULTS

The monosyllabic word scores of CI-1 were excellent in Groups A (91.7±7.9%) and B (92.5±3.6%) but slightly lower in Group C (85.7±14.9%) before the second implantation (P = .487). At 3 years after the second implantation, all groups demonstrated excellent scores in the bilateral CI condition (95.9±3.0% in Group A; 99.1±.8% in Group B; 97.5±2.9% in Group C, P = .600). However, when the patients were tested in using CI-2 only in Groups A and B after using bilateral CI for 3 years, the scores were inconsistent in Group A (79.6±23.9%; range: 22.2-94.4%), while those were higher and more constant in Group B (92.9±4.8%; 86.8-100.0%).

CONCLUSIONS

The first CI is strongly recommended to perform on a worse hearing ear if they had different hearing levels between ears. Even with the first CI on a worse hearing ear, its performance never deteriorates. In addition, if they receive the second CI several years later, it will be likely that the second one functions better.

Review of Binaural Processing With Asymmetrical Hearing Outcomes in Patients With Bilateral Cochlear Implants

Bilateral cochlear implants (BiCIs) result in several benefits, including improvements in speech understanding in noise and sound source localization. However, the benefit bilateral implants provide among recipients varies considerably across individuals. Here we consider one of the reasons for this variability: difference in hearing function between the two ears, that is, interaural asymmetry. Thus far, investigations of interaural asymmetry have been highly specialized within various research areas. The goal of this review is to integrate these studies in one place, motivating future research in the area of interaural asymmetry. We first consider bottom-up processing, where binaural cues are represented using excitation-inhibition of signals from the left ear and right ear, varying with the location of the sound in space, and represented by the lateral superior olive in the auditory brainstem. We then consider top-down processing via predictive coding, which assumes that perception stems from expectations based on context and prior sensory experience, represented by cascading series of cortical circuits. An internal, perceptual model is maintained and updated in light of incoming sensory input. Together, we hope that this amalgamation of physiological, behavioral, and modeling studies will help bridge gaps in the field of binaural hearing and promote a clearer understanding of the implications of interaural asymmetry for future research on optimal patient interventions.

Sound source localization patterns and bilateral cochlear implants: Age at onset of deafness effects

The ability to determine a sound’s location is critical in everyday life. However, sound source localization is severely compromised for patients with hearing loss who receive bilateral cochlear implants (BiCIs). Several patient factors relate to poorer performance in listeners with BiCIs, associated with auditory deprivation, experience, and age. Critically, characteristic errors are made by patients with BiCIs (e.g., medial responses at lateral target locations), and the relationship between patient factors and the type of errors made by patients has seldom been investigated across individuals. In the present study, several different types of analysis were used to understand localization errors and their relationship with patient-dependent factors (selected based on their robustness of prediction). Binaural hearing experience is required for developing accurate localization skills, auditory deprivation is associated with degradation of the auditory periphery, and aging leads to poorer temporal resolution. Therefore, it was hypothesized that earlier onsets of deafness would be associated with poorer localization acuity and longer periods without BiCI stimulation or older age would lead to greater amounts of variability in localization responses. A novel machine learning approach was introduced to characterize the types of errors made by listeners with BiCIs, making them simple to interpret and generalizable to everyday experience. Sound localization performance was measured in 48 listeners with BiCIs using pink noise trains presented in free-field. Our results suggest that older age at testing and earlier onset of deafness are associated with greater average error, particularly for sound sources near the center of the head, consistent with previous research. The machine learning analysis revealed that variability of localization responses tended to be greater for individuals with earlier compared to later onsets of deafness. These results suggest that early bilateral hearing is essential for best sound source localization outcomes in listeners with BiCIs.

The Effect of Cochlear Implant Interval on Spoken Language Skills of Pediatric Bilateral Cochlear Implant Users

OBJECTIVE

To examine the effects of cochlear implant (CI) interval (time between CI surgeries) on receptive vocabulary and receptive language skills for children with bilateral CIs.

STUDY DESIGN

A prospective cross-sectional study design.

SETTING

Participants were recruited from, and tested at, oral schools for the deaf and pediatric audiology clinics across the United States.

PATIENTS

Eighty-eight children, 4 to 9 years of age, with bilateral CIs and known hearing histories. Twenty-three participants received CIs simultaneously and 65 received CIs sequentially. Of those implanted sequentially, 86% wore a hearing aid (HA) on the non-implanted ear during the CI interval.

INTERVENTION

Bilateral cochlear implantation.

MAIN OUTCOME MEASURES

Receptive vocabulary was measured via the Peabody Picture Vocabulary Test (PPVT). Receptive language skills were measured via the Clinical Evaluation of Language Fundamentals (CELF).

RESULTS

Multiple linear regression models indicate better receptive vocabulary and receptive language skills are associated with earlier ages at first CI (CI 1), but not with shorter CI intervals.

CONCLUSIONS

Early cochlear implantation (i.e., age at CI 1) is critical for better receptive vocabulary and receptive language skills. Shorter CI intervals are not associated with better receptive vocabulary and receptive language skills for these 88 children, who nearly all used bimodal hearing during the interval. Use of a HA at the non-implanted ear, before receipt of a second CI (CI 2), may mitigate the effects of early bilateral auditory deprivation.

A Longitudinal Study in Children With Sequential Bilateral Cochlear Implants: Time Course for the Second Implanted Ear and Bilateral Performance

PURPOSE

Whether, and if so when, a second-ear cochlear implant should be provided to older, unilaterally implanted children is an ongoing clinical question. This study evaluated rate of speech recognition progress for the second implanted ear and with bilateral cochlear implants in older sequentially implanted children and evaluated localization abilities.

METHOD

A prospective longitudinal study included 24 bilaterally implanted children (mean ear surgeries at 5.11 and 14.25 years). Test intervals were every 3-6 months through 24 months postbilateral. Test conditions were each ear and bilaterally for speech recognition and localization.

RESULTS

Overall, the rate of progress for the second implanted ear was gradual. Improvements in quiet continued through the second year of bilateral use. Improvements in noise were more modest and leveled off during the second year. On all measures, results from the second ear were poorer than the first. Bilateral scores were better than either ear alone for all measures except sentences in quiet and localization.

CONCLUSIONS

Older sequentially implanted children with several years between surgeries may obtain speech understanding in the second implanted ear; however, performance may be limited and rate of progress gradual. Continued contralateral ear hearing aid use and reduced time between surgeries may enhance outcomes.

United Kingdom national paediatric bilateral project: Demographics and results of localization and speech perception testing

OBJECTIVES

To assess longitudinal outcomes in a large and varied population of children receiving bilateral cochlear implants both simultaneously and sequentially.

METHODS

This observational non-randomized service evaluation collected localization and speech recognition in noise data from simultaneously and sequentially implanted children at four time points: before bilateral cochlear implants or before the sequential implant, 1 year, 2 years, and 3 years after bilateral implants. No inclusion criteria were applied, so children with additional difficulties, cochleovestibular anomalies, varying educational placements, 23 different home languages, a full range of outcomes and varying device use were included.

RESULTS

1001 children were included: 465 implanted simultaneously and 536 sequentially, representing just over 50% of children receiving bilateral implants in the UK in this period. In simultaneously implanted children the median age at implant was 2.1 years; 7% were implanted at less than 1 year of age. In sequentially implanted children the interval between implants ranged from 0.1 to 14.5 years. Children with simultaneous bilateral implants localized better than those with one implant. On average children receiving a second (sequential) cochlear implant showed improvement in localization and listening in background noise after 1 year of bilateral listening. The interval between sequential implants had no effect on localization improvement although a smaller interval gave more improvement in speech recognition in noise. Children with sequential implants on average were able to use their second device to obtain spatial release from masking after 2 years of bilateral listening. Although ranges were large, bilateral cochlear implants on average offered an improvement in localization and speech perception in noise over unilateral implants.

CONCLUSION

These data represent the diverse population of children with bilateral cochlear implants in the UK from 2010 to 2012. Predictions of outcomes for individual patients are not possible from these data. However, there are no indications to preclude children with long inter-implant interval having the chance of a second cochlear implant.

Bilateral cochlear implants in children: Effects of auditory experience and deprivation on auditory perception

Spatial hearing skills are essential for children as they grow, learn and play. These skills provide critical cues for determining the locations of sources in the environment, and enable segregation of important sounds, such as speech, from background maskers or interferers. Spatial hearing depends on availability of monaural cues and binaural cues. The latter result from integration of inputs arriving at the two ears from sounds that vary in location. The binaural system has exquisite mechanisms for capturing differences between the ears in both time of arrival and intensity. The major cues that are thus referred to as being vital for binaural hearing are: interaural differences in time (ITDs) and interaural differences in levels (ILDs). In children with normal hearing (NH), spatial hearing abilities are fairly well developed by age 4-5 years. In contrast, most children who are deaf and hear through cochlear implants (CIs) do not have an opportunity to experience normal, binaural acoustic hearing early in life. These children may function by having to utilize auditory cues that are degraded with regard to numerous stimulus features. In recent years there has been a notable increase in the number of children receiving bilateral CIs, and evidence suggests that while having two CIs helps them function better than when listening through a single CI, these children generally perform worse than their NH peers. This paper reviews some of the recent work on bilaterally implanted children. The focus is on measures of spatial hearing, including sound localization, release from masking for speech understanding in noise and binaural sensitivity using research processors. Data from behavioral and electrophysiological studies are included, with a focus on the recent work of the authors and their collaborators. The effects of auditory plasticity and deprivation on the emergence of binaural and spatial hearing are discussed along with evidence for reorganized processing from both behavioral and electrophysiological studies. The consequences of both unilateral and bilateral auditory deprivation during development suggest that the relevant set of issues is highly complex with regard to successes and the limitations experienced by children receiving bilateral cochlear implants. This article is part of a Special Issue entitled .

The effect of early auditory experience on the spatial listening skills of children with bilateral cochlear implants

OBJECTIVES

Both electrophysiological and behavioural studies suggest that auditory deprivation during the first months and years of life can impair listening skills. Electrophysiological studies indicate that 3½ years may be a critical age for the development of symmetrical cortical responses in children using bilateral cochlear implants. This study aimed to examine the effect of auditory experience during the first 3½ years of life on the behavioural spatial listening abilities of children using bilateral cochlear implants, with reference to normally hearing children. Data collected during research and routine clinical testing were pooled to compare the listening skills of children with bilateral cochlear implants and different periods of auditory deprivation.

METHODS

Children aged 4-17 years with bilateral cochlear implants were classified into three groups. Children born profoundly deaf were in the congenital early bilateral group (received bilateral cochlear implants aged ≤3½ years, n=28) or congenital late bilateral group (received first implant aged ≤3½ years and second aged >3½ years, n=38). Children with some bilateral acoustic hearing until the age of 3½ years, who subsequently became profoundly deaf and received bilateral cochlear implants, were in the acquired/progressive group (n=16). There were 32 children in the normally hearing group. Children completed tests of sound-source localization and spatial release from masking (a measure of the ability to use both ears to understand speech in noise).

RESULTS

The acquired/progressive group localized more accurately than both groups of congenitally deaf children (p<0.05). All three groups of children with cochlear implants showed similar spatial release from masking. The normally hearing group localized more accurately than all groups with bilateral cochlear implants and displayed more spatial release from masking than the congenitally deaf groups on average (p<0.05).

CONCLUSION

Children with bilateral cochlear implants and early experience of acoustic hearing showed more accurate localization skills, on average, than children born profoundly deaf.

Simultaneous bilateral cochlear implantation in a five-month-old child with Usher syndrome

OBJECTIVE

To report a rare case of simultaneous bilateral cochlear implantation in a five-month-old child with Usher syndrome.

METHOD

Case report.

RESULTS

A five-month-old boy with Usher syndrome and congenital profound bilateral deafness underwent simultaneous bilateral cochlear implantation. The decision to perform implantation in such a young child was based on his having a supportive family and the desire to foster his audiological development before his vision deteriorated. The subject experienced easily resolvable intra- and post-operative adverse events, and was first fitted with an externally worn audio processor four weeks after implantation. At 14 months of age, his audiological development was age-appropriate.

CONCLUSION

Simultaneous bilateral cochlear implantation is possible, and even advisable, in children as young as five months old when performed by an experienced implantation team.

Asymmetric Hearing During Development: The Aural Preference Syndrome and Treatment Options

Deafness affects ∼2 in 1000 children and is one of the most common congenital impairments. Permanent hearing loss can be treated by fitting hearing aids. More severe to profound deafness is an indication for cochlear implantation. Although newborn hearing screening programs have increased the identification of asymmetric hearing loss, parents and caregivers of children with single-sided deafness are often hesitant to pursue therapy for the deaf ear. Delayed intervention has consequences for recovery of hearing. It has long been reported that asymmetric hearing loss/single-sided deafness compromises speech and language development and educational outcomes in children. Recent studies in animal models of deafness and in children consistently show evidence of an "aural preference syndrome" in which single-sided deafness in early childhood reorganizes the developing auditory pathways toward the hearing ear, with weaker central representation of the deaf ear. Delayed therapy consequently compromises benefit for the deaf ear, with slow rates of improvement measured over time. Therefore, asymmetric hearing needs early identification and intervention. Providing early effective stimulation in both ears through appropriate fitting of auditory prostheses, including hearing aids and cochlear implants, within a sensitive period in development has a cardinal role for securing the function of the impaired ear and for restoring binaural/spatial hearing. The impacts of asymmetric hearing loss on the developing auditory system and on spoken language development have often been underestimated. Thus, the traditional minimalist approach to clinical management aimed at 1 functional ear should be modified on the basis of current evidence.