BACKGROUND ON COCHLEAR IMPLANTS
Age of Onset of Deafness: The age of onset continues to have important implications for cochlear implantation, depending on whether the hearing impairment occurred before (prelingual), during (perilingual), or after (postlingual) learning speech and language. At the time of the last CDC, data on cochlear implantation suggested that children or adults with postlingual onset of deafness had better auditory performance than children or adults with prelingual or perilingual onsets. On average, current data following auditory performance in children over a longer period of time support this finding. However, the difference between children with postlingual and prelingual-perilingual onsets appears to lessen with time. Large individual differences remain within each group.
Age at Implantation: Previous data suggested that prelingually or perilingually deafened persons who were implanted in adolescence or adulthood did not achieve as good auditory performance as those implanted during childhood, although individual differences were recognized. Current data continue to support the importance of early detection of hearing loss and implantation for maximal auditory performance. However, it is still unclear whether implantation at age 2, for example, ultimately results in better auditory performance than implantation at age 3.
Duration of Deafness: As deafness endures, even in postlingually deafened individuals, some acquired skills and knowledge may decline and some behaviors that work against successful adaptation to a sensory device may develop. Individuals with shorter durations of auditory deprivation tend to achieve better auditory performance from any type of sensory aid, including cochlear implants, than individuals with longer durations of auditory deprivation.
Benefits and Limitations of Cochlear Implantation: Impact on Speech Perception in Adults
Cochlear implantation has a profound impact on hearing and speech reception in postlingually deafened adults. Most individuals demonstrate significantly enhanced speech-reading capabilities, attaining scores of 90-100 percent correct on everyday sentence materials. Speech recognition afforded by the cochlear implant effectively supplements the information least favorably cued through speech-reading. A majority of those individuals with the latest speech processors for their implants will score above 80-percent correct on high-context sentences without visual cues. Performance on single-word testing in these individuals is notably poorer, although even these scores have been significantly improved with newer speech-processing strategies. Recognition of environmental sounds and even appreciation of music have been repeatedly observed in adult implant recipients. Noisy environments remain a problem for cochlear-implanted adults, significantly detracting from speech-perception abilities. Prelingually deafened adults have generally shown little improvement in speech perception scores after cochlear implantation. Many individuals derive satisfaction from hearing environmental sounds and continue to use their implants.
Speech Perception, Speech Production, and Language Acquisition in Children: Improvements in the speech perception and speech production of children following cochlear implantation are often reported as primary benefits. Variability across children is substantial. Factors such as age of onset, age of implantation, the nature and intensity of (re)habilitation, and mode of communication contribute to this variability. Using tests commonly applied to children and adults with hearing impairments (e.g., pattern perception, closed-set word identification, and open-set perception), perceptual performance increases on average with each succeeding year post implantation. Shortly after implantation, performance may be broadly comparable to that of some children with hearing aids and over time may improve to match that of children who are highly successful hearing aid users. Children implanted at younger ages are on average more accurate in their production of consonants, vowels, intonation, and rhythm. Speech produced by children with implants is more accurate than speech produced by children with comparable hearing losses using vibro-tactile or hearing aids. One year after implantation, speech intelligibility is twice that typically reported for children with profound hearing impairments and continues to improve. Oral-aural communication training appears to result in substantially greater speech intelligibility than manually based total communication The language outcomes in children with cochlear implants have received less attention. Reports involving small numbers of children suggest that implantation in conjunction with education plus habilitation leads to advances in oral language acquisition. The nature and pace of language acquisition may be influenced by the age of onset, age at implantation, nature and intensity of habilitation, and mode of communication. One current limitation is that children are typically implanted at no earlier than age 2 years, which is beyond what may be critical periods of auditory input for the acquisition of oral language. Benefits are not realized immediately, but rather are manifested over time, with some children continuing to show improvement over several years. Few studies have used language as an outcome measure. The assessment of speech perception, language production, and language comprehension in young children is particularly challenging. Furthermore, all results in children have been reported for single-channel or feature-based devices only, despite the relatively rapid evolution of alternatives in speech-coding strategies. Oral language development in deaf children, including those with cochlear implants, remains a slow, training-intensive process, and results will typically be delayed in comparison with normally hearing peers.
Psychologic and Social Issues in Adults and Children: Although psychological evaluation has previously been a part of the preimplant evaluation process, comparatively little research has been conducted on the long-term psychological and social effects of electing for implantation. Still, the psychological and social impact for adults is generally quite positive, and there appears to be agreement between preimplantation expectations and later benefit. This benefit is expressed as a decline in loneliness, depression and social isolation and an increase in self-esteem, independence, social integration, and vocational prospects.Many adults report being able to function socially or vocationally in ways comparable to those with moderate hearing loss. Furthermore, they describe a new or renewed curiosity about the experience of hearing and the phenomena of sound. In some cases the experience of implantation becomes an integral part of the individual's identity, leading implant users to participate and share experiences in self-interest and advocacy groups. Negative psychological and social impact is less frequently observed and is often related to concerns about the maintenance and/or malfunction of the implant and external hardware. Other social insecurities may result from the difficulty of hearing amidst background noise, and from unreasonable expectations of aural-only benefit on the part of the implant user or his/her family and friends. The assessment of psychological impact in children with implants lags behind that for the adult population, in part because psychological outcome is a factor of audiological benefit, which is realized more slowly in children. Additionally, such assessment must consider the child's family setting. Because language acquisition is closely associated with identity, social development, and social integration, the impact of implantation on a child's development in these areas deserves more study in order to produce useful indicators that can bear upon parental decision-making processes.
Rehabilitation and Educational Issues: Pediatric cochlear implantation requires a multidisciplinary team composed of physicians, audiologists, speech-language pathologists, rehabilitation specialists, and educators familiar with cochlear implants. These professionals must work together in a long-term relationship to support the child's auditory and oral development. Although the effects of communication mode in implantation habilitation have not been sufficiently documented, it is clear that the educational programs for children with cochlear implants must include auditory and speech instruction using the auditory information offered by the implant.
Surgical Issues: Cochlear implantation entails risks common to most surgical procedures, e.g., general anesthetic exposure, as well as unique risks that are influenced by device design, individual anatomy and pathology, and surgical technique. Comparative data of major complications incurred in adult implantation show a halving of the complication rate to approximately 5 percent in 1993. The complication rate in pediatric implantation is less than that currently seen in adults. Overall, the complication rate compares favorably to the 10 percent rate seen with pacemaker/defibrillator implantation. Major complications, i.e., those requiring revision surgery, include flap problems, device migration or extrusion, and device failure. Facial palsy is also considered a major complication but is distinctly uncommon and rarely permanent. Notably, no mortalities have been attributed to cochlear implantation. Alterations in surgical technique, especially flap design, have led to a considerable reduction in the flap complication rate, which is particularly relevant to transcutaneous devices. Alterations in surgical technique, particularly in methods used to anchor the device, have contributed to a decrease in device migration/extrusion. All implants are potentially prone to failure--either because of manufacturing defects or use- related trauma. Pedestal fracture is a problem unique to the percutaneous device, but occurs rarely. Manufacturer redesign has produced electrode arrays that are smaller but sturdier. For the most commonly implanted device, 95 percent of implants are still functioning after 9 years. Most current implants with transcutaneous connectors do not provide self-test capability for the implanted portion, making it cumbersome to test for simple electrode failure, such as open and short circuits. Failure detection is particularly problematic in young children. Device manufacturers should include self-test circuitry in future implant designs. Minor complications are those that resolve without surgical intervention. The most common is unwanted facial nerve stimulation with electrode activation, which is readily rectified by device reprogramming. In percutaneous devices, pedestal infections are uncommon and can be treated successfully with antibiotics, but on rare occasions may require explantation. Reimplantation is necessary in approximately 5 percent of cases because of improper electrode insertion or migration, device failure, serious flap complication, or loss of manufacturer support. In general, reimplantation in the same ear is usually possible, and thus far individual auditory performance after reimplantation equals or exceeds that seen with the original implant. Long-term complications of implantation relate to flap breakdown, electrode migration and receiver/stimulator migration. Particularly in the child, the potential consequences of otitis media have been of concern, but as the implanted electrode becomes ensheathed in a fibrous envelope, it appears protected from the consequences of local infection.
Children: Cochlear implants have also been shown to result in successful speech perception in children. Currently, the earliest age of implantation is 24 months, but there are reasons to reassess this age threshold. A younger age of implantation may limit the negative consequences of auditory deprivation and may allow more efficient acquisition of speech and language. Determining whether cochlear implant benefits are greater in children implanted at age 2-3 years as compared to those implanted at age 4-5 years might resolve this issue, but sufficient data are unavailable. It is also not clear that the benefits of implantation before age 2 years would offset potential liabilities associated with the increased difficulty in obtaining reliable and valid characterization of hearing and functional communication status at the younger age. A number of children under age 2 years have received implants, both internationally and in the United States, when it was thought that bone growth associated with meningitis would preclude implantation at a later date. Speech/language data obtained on such children will be helpful in determining the potential benefits of early implantation and therefore may help to guide future policy.
Audiologic Criteria: Children age 2 years or older with profound (greater than 90 dBHL) sensorineural hearing loss bilaterally and minimal speech perception under best aided conditions may be considered for cochlear implantation. In the young child, auditory brainstem response, stapedial reflex testing, and/or otoacoustic emission testing may be useful when combined with auditory behavioral responses to determine hearing status. Prior to implantation, a trial period with appropriate amplification combined with intensive auditory training should have been attempted to ensure that maximal benefit has been achieved. When the validity of behavioral test results is compromised by maturational factors, the above criteria should be applied in the most stringent manner (i.e., worse hearing sensitivity, longer trial periods, and so on). Current research may broaden audiometric criteria for candidacy to better reflect functional auditory capacity.
Medical and Surgical Criteria:Children should undergo a complete medical evaluation to rule out the presence of active disease, which would be a contraindication to surgery. The child must be otologically stable and free of active middle ear disease prior to cochlear implantation. The radiologic imaging criteria used in adult candidates can be applied to children.
Psychosocial Criteria: Preoperative assessment should entail evaluation of the child in the context of the home and social and educational milieu to assure that implantation is the proper intervention. In some instances psychosocial factors may be used as exclusionary criteria; however, in most cases it should serve only as baseline data for tracking cochlear implant outcomes.
Informed Consent: The parents of a deaf child are responsible for deciding whether to elect cochlear implantation. The informed consent process should be used to empower parents in their decision-making. The parents must understand that cochlear implants do not restore normal hearing and that auditory and speech outcomes are highly variable and unpredictable. They must be informed of the advantages, disadvantages, and risks associated with implantation to establish realistic expectations. Furthermore, the importance of long-term rehabilitation to success with cochlear implants must be stressed. As part of the process of informed consent, parents must be told that alternative approaches to habilitation are available. All children should be included in the informed consent process to the extent they are able, as their active participation is crucial to (re)habilitative success.
Directions for Future Research on Cochlear Implantation: Research must attempt to explain the wide variation in performance across individual cochlear implant users. New tools, such as functional imaging of the brain, might be applied to unexplored variables such as the ability of the implant to activate the central auditory system. Investigations of the role of higher level cognitive processes in cochlear implant performance are needed.
The strides that have been made in improving speech perception of cochlear implant users should continue through improvements in electrode design and signal processing strategies. Noise-reduction technologies and enhancement of performance using binaural implants are promising areas.
Studies of the effects of cochlear stimulation on auditory neurons have provided clear evidence of plasticity in both the survival of neural elements and in receptive field organization. Comparisons of neural plasticity in animal experiments and of adaptation to cochlear implant electrical stimulation by humans provide a unique opportunity to study the relationships between neural activity and auditory perception.
Comparative research on language development in children with normal hearing, children with hearing impairment who use hearing aids, deaf children with cochlear implants, and deaf children using American Sign Language should be conducted. These studies should be longitudinal and reflect current theoretical and empirical advances in neurolinguistics and psycholinguistics.
Studies of the relationship between the development of speech perception and speech production in cochlear implant users must continue. Implanted deaf children provide a unique opportunity to examine these developmental processes and their relationship to the acquisition of aural/oral language. Such information is crucial to understanding and enhancing the performance of implanted prelingual children and may help define optimal age for implantation.
Adequate tools for the assessment of nonspeech benefits of implantation should be applied to gain a better understanding of the full effects of implantation on the quality of life of implant recipients. This may be particularly useful for implant recipients who do not realize significant speech-perception benefit. Such data will help in evaluating the cost-utility of cochlear implantation.
Identifying the components of successful (re)habilitation approaches will facilitate extension of these services to all children and adults receiving cochlear implants, as will comparison of model and routine service programs.
Conclusions: Cochlear implantation improves communication ability in most adults with deafness and frequently leads to positive psychological and social benefits as well. The greatest benefits seen to date have occurred in postlingually deafened adults. Cochlear implantation in prelingually deafened adults provides more limited improvement in speech perception, but offers important environmental sound awareness. Cochlear implantation outcomes are more variable in children. Nonetheless, gradual, steady improvement in speech perception, speech production, and language does occur. There is substantial unexplained variability in the performance of implant users of all ages, and implants are not appropriate for all individuals. Currently children at least 2 years old and adults with profound deafness are candidates for implantation. Cochlear implant candidacy should be extended to adults with severe hearing impairment and poor open-set sentence discrimination, i.e., less than or equal to 30 percent in the best aided condition. Although there are theoretical reasons to lower the age of implantation in children, data are too scarce to justify a change in criteria. Additional data may justify a change in age and audiologic criteria. Auditory performance with a cochlear implant varies among individuals. The data indicate that performance is better in individuals who (1) have shorter durations of deafness, (2) were implanted before age 6 years, and (3) acquired language before their hearing loss occurred. Auditory performance is not affected by etiology of hearing loss. Access to optimal educational and (re)habilitation services is important to adults and is critical to children to maximize the benefits available from cochlear implantation. The current generation of intracochlear, multichannel implants with spectrally based speech processors provides a substantial improvement over the previous generation of devices, especially when nonsimultaneous electrode activation is used. The low complication rate and high reliability for cochlear implants compares favorably with other implanted electronic devices, and continues to improve. Current devices are not MRI compatible, and users and physicians should be acutely aware of this problem. Implant manufacturers should include MRI compatibility and internal self-test systems in future devices. Percutaneous connectors offer many research and clinical opportunities, including MRI compatibility, ease of electrode testing, and processor upgrades, and they should not be abandoned.
Dr. William Luxford, House Ear Institute
Access to the world of education, social contacts, etc., as an hearing child.
Possible avoidance of being labeled, teased, isolated, etc. as a 'disabled' person.
Ability to be aware of sounds, like someone who was born hearing and later lost his hearing. There is anecdotal evidence that people with this ability later become excellent lipreaders.
(Information is up to
date as of November 1993.)
Summary of opinions against cochlear implants
Several implanted children derive little or no benefit from the implantation even after long auditory therapy, so they do not in fact gain enough access to language at the critical age for language acquisition using the oral method.
Due to the length of therapy, some children, who might benefit from CI, may realize the benefit only after they passed the critical age for language acquisition using the oral method.
Invasive surgical procedure, which has its risks.
Possible risks include dizziness and very mild form of eczema.
People who are implanted face risk from very strong magnetic fields (due either to pulling of magnetizable metals by the magnetic field or to induction currents from time-varying magnetic fields). Thus they cannot safely work at jobs which require working with very strong magnetic fields (such as practicing some fields of experimental physics).
The MRI non-invasive medical examination method is dangerous to people with implants, due to its usage of very strong magnetic fields.
The long-range Safety of the procedure in children was not conclusively established, especially the long-range effects, and in particular, the effect of the child's growth on positioning of the implant in the cochlea.
Implanting a child may cause his parents and teachers to neglect more traditional (and successful) methods of deaf education, in the mistaken belief that the child can be considered to be "hearing".
The implanted child is being 'married' for life to a group of medical experts who will monitor his cochlear implant operation and adjust his speech processor.
The implanted child would have the non-healthy self-concept of having had something wrong with his body, which was (partially, because cochlear implants are not perfect substitute to normal hearing) fixed - rather than having the healthy self-concept of a proud Deaf.
An implanted child is liable to being labeled or teased, due to his being special in having an implant in his ear and carrying a signal processor on his person.
This Page Created by AAAdvanced Engineering Concepts
Send Questions or Comments to: firstname.lastname@example.org
Copyright © 2003