Effect of age at onset of deafness on children's speech perception abilities with a cochlear implant

The role of age on speech development in subjects with cochlear implants

The cochlear implant has been approved as a method of treating bilateral deep deafness since the 1980s, and since then candidate selection methods have changed several times. Initially, the candidates were only adult patients, and in 1990 the cochlear implant was approved for the first time in children under 2 years of age by the US Food and Drug Administration. In 2000, the same US Administration reduced the limit to one year. The aim of this study was to determine the effect of age at cochlear implantation on speech recognition abilities. Concerning the age groups in which the subjects were assigned to, the best results on the tests were achieved by the group who underwent cochlear implantation at the youngest age. In conclusion, the benefit from cochlear implant in subjects with pre-lingual hearing impairment of the most severe degree has to be stressed and it is much bigger in comparison to individual amplifying hearing aids. If cochlear implant is placed at the youngest age, the results might lead to even 100% of active involvement in the social life of individuals with this kind of impairment.

Parental restriction of children's access to cochlear implants: case studies

This article reports on four retrospective case studies in which parental behavioral management of the implanted child included withholding the cochlear implant or activities associated with it as a disciplinary measure or as a means of preventing device loss or damage. The need for parental counseling by health care and educational professionals as to the importance of a child's connection to the hearing world all day long through the implant for optimal speech, language, academic, and psychosocial development is emphasized.

Working memory in children with cochlear implants: problems are in storage, not processing

BACKGROUND

There is growing consensus that hearing loss and consequent amplification likely interact with cognitive systems. A phenomenon often examined in regards to these potential interactions is working memory, modeled as consisting of one component responsible for storage of information and another component responsible for processing of that information. Signal degradation associated with cochlear implants should selectively inhibit storage without affecting processing. This study examined two hypotheses: (1) A single task can be used to measure storage and processing in working memory, with recall accuracy indexing storage and rate of recall indexing processing; (2) Storage is negatively impacted for children with CIs, but not processing.

METHOD

Two experiments were conducted. Experiment 1 included adults and children, 8 and 6 years of age, with NH. Procedures tested the prediction that accuracy of recall could index storage and rate of recall could index processing. Both measures were obtained during a serial-recall task using word lists designed to manipulate storage and processing demands independently: non-rhyming nouns were the standard condition; rhyming nouns were predicted to diminish storage capacity; and non-rhyming adjectives were predicted to increase processing load. Experiment 2 included 98 8-year-olds, 48 with NH and 50 with CIs, in the same serial-recall task using the non-rhyming and rhyming nouns.

RESULTS

Experiment 1 showed that recall accuracy was poorest for the rhyming nouns and rate of recall was slowest for the non-rhyming adjectives, demonstrating that storage and processing can be indexed separately within a single task. In Experiment 2, children with CIs showed less accurate recall of serial order than children with NH, but rate of recall did not differ. Recall accuracy and rate of recall were not correlated in either experiment, reflecting independence of these mechanisms.

CONCLUSIONS

It is possible to measure the operations of storage and processing mechanisms in working memory in a single task, and only storage is impaired for children with CIs. These findings suggest that research and clinical efforts should focus on enhancing the saliency of representation for children with CIs. Direct instruction of syntax and semantics could facilitate storage in real-world working memory tasks.

Communication development in children who receive a cochlear implant by 12 months of age

OBJECTIVE

Describe the long-term benefits of early cochlear implantation. Provide a comprehensive description of outcomes, including: language, speech production, and speech perception. Compare the communication outcomes for the early implanted children to those of normally hearing children and children who received a cochlear implant at a comparatively older age.

METHOD

Retrospective review of the communication development of 35 children implanted between 6 and 12 months of age and 85 children implanted between 13 and 24 months of age. Audiologic assessments included unaided and aided audiograms, auditory brainstem response (ABR), auditory steady state response (ASSR), and otoacoustic emissons (OAEs). Formal language, speech production, and speech perception measures were administered, preimplant and at 1, 2, 3, and 5 years postimplant.

RESULTS

The children who received their cochlear implant by 12 months of age demonstrated language growth rates equivalent to their normally hearing peers and achieved age appropriate receptive language scores 3 years postimplant. The children who received their cochlear implant between 13 and 24 months demonstrated a significant language delay at 3 years postimplant. Speech production development followed a similar pattern to that of normal-hearing children, although was delayed, for both groups of children. Mean open-set speech perception scores were comparable with previous reports for children and adults who use cochlear implants.

CONCLUSION

Children implanted by 12 months of age demonstrate better language development compared with children who receive their cochlear implant between 13 and 24 months. This supports the provision of a cochlear implant within the first year of life to enhance the likelihood that a child with severe-to-profound hearing impairment will commence elementary school with age-appropriate language skills.

Altered intra- and inter-regional synchronization of superior temporal cortex in deaf people

Functional organization of the brain can be fundamentally altered by auditory deprivation. Previous studies found that the superior temporal cortex in deaf people is reorganized to process non-auditory stimuli, as revealed by the extrinsic task-induced brain activities. However, it is unknown how the intrinsic activities of this region are impacted by deafness. This study explored this issue using resting-state functional magnetic resonance imaging. We examined 60 congenitally deaf (CD) individuals, 39 acquired deaf (AD) individuals, and 38 hearing controls (HC), and focused on the effect of deafness on the intra- and inter-regional synchronization of different parts of superior temporal sulcus (STS). We found that intra-regional synchronization or regional homogeneity (ReHo) of the middle STS (mSTS) was decreased in AD compared with HC or CD, while the CD had preserved ReHo in mSTS. Greater connectivity was observed between mSTS and posterior STS in CD and HC than in AD, while both CD and AD had weaker connectivity of mSTS with the anterior STS (aSTS) compared with HC. Moreover, the connectivity of mSTS-aSTS in CD and AD was associated with their language skills. These findings confirmed our hypothesis that the intrinsic function of different parts of STS is distinctly impacted by deafness.

Brain activations associated with sign production using word and picture inputs in deaf signers

Effective literacy education in deaf students calls for psycholinguistic research revealing the cognitive and neural mechanisms underlying their written language processing. When learning a written language, deaf students are often instructed to sign out printed text. The present fMRI study was intended to reveal the neural substrates associated with word signing by comparing it with picture signing. Native deaf signers were asked to overtly sign in Chinese Sign Language (CSL) common objects indicated with written words or presented as pictures. Except in left inferior frontal gyrus and inferior parietal lobule where word signing elicited greater activation than picture signing, the two tasks engaged a highly overlapping set of brain regions previously implicated in sign production. The results suggest that word signing in the deaf signers relies on meaning activation from printed visual forms, followed by similar production processes from meaning to signs as in picture signing. The present study also documents the basic brain activation pattern for sign production in CSL and supports the notion of a universal core neural network for sign production across different sign languages.

Neural prostheses and brain plasticity

The success of modern neural prostheses is dependent on a complex interplay between the devices' hardware and software and the dynamic environment in which the devices operate: the patient's body or 'wetware'. Over 120 000 severe/profoundly deaf individuals presently receive information enabling auditory awareness and speech perception from cochlear implants. The cochlear implant therefore provides a useful case study for a review of the complex interactions between hardware, software and wetware, and of the important role of the dynamic nature of wetware. In the case of neural prostheses, the most critical component of that wetware is the central nervous system. This paper will examine the evidence of changes in the central auditory system that contribute to changes in performance with a cochlear implant, and discuss how these changes relate to electrophysiological and functional imaging studies in humans. The relationship between the human data and evidence from animals of the remarkable capacity for plastic change of the central auditory system, even into adulthood, will then be examined. Finally, we will discuss the role of brain plasticity in neural prostheses in general.

A comparison of cochlear implant processing strategies in children using speech pattern audiometry

The aim of this study was to use Speech Pattern Audiometry (SPA) to compare phoneme perception performance between SPEAK and ACE processing strategies with children using the Nucleus 24 cochlear implant. Listeners were evaluated in terms of ability to identify two synthetic word pairs, one signalling a voicing contrast and the other signalling a place of articulation contrast. For both word pairs, ACE was associated with more 'normal' phoneme boundaries than SPEAK. There was also a non-significant trend for better identification ability with ACE compared to SPEAK. The study suggests that there may be a place for SPA as part of the clinical battery of tests used for evaluation of cochlear implant speech processing strategies in children. Copyright (c) 2005 John Wiley & Sons, Ltd.

Cochlear implants and brain plasticity

Cochlear implants have been implanted in over 110,000 deaf adults and children worldwide and provide these patients with important auditory cues necessary for auditory awareness and speech perception via electrical stimulation of the auditory nerve (AN). In 1942, Woolsey and Walzl presented the first report of cortical responses to localised electrical stimulation of different sectors of the AN in normal hearing cats, and established the cochleotopic organization of the projections to primary auditory cortex. Subsequently, individual cortical neurons in normal hearing animals have been shown to have well characterized input-output functions for electrical stimulation and decreasing response latencies with increasing stimulus strength. However, the central auditory system is not immutable, and has a remarkable capacity for plastic change, even into adulthood, as a result of changes in afferent input. This capacity for change is likely to contribute to the ongoing clinical improvements observed in speech perception for cochlear implant users. This review examines the evidence for changes of the response properties of neurons in, and consequently the functional organization of, the central auditory system produced by chronic, behaviourally relevant, electrical stimulation of the AN in profoundly deaf humans and animals.

Childhood Development after Cochlear Implantation (CDaCI) study: design and baseline characteristics

Children with severe to profound sensorineural hearing loss face communication challenges that influence language, psychosocial and scholastic performance. Clinical studies over the past 20 years have supported wider application of cochlear implants in children. The Childhood Development after Cochlear Implantation (CDaCI) study is the first longitudinal multicentre, national cohort study to evaluate systematically early cochlear implant (CI) outcomes in children. The objective of the study was to compare children who have undergone cochlear implantation, with similarly aged hearing peers across multiple domains, including oral language development, auditory performance, psychosocial and behavioural functioning, and quality of life. The CDaCI study is a multicentre national cohort study of CI children and normal hearing (NH) peers. Eligibility criteria include informed consent, age less than 5 years, pre- or post-lingually deaf, developmental criteria met, commitment to educate the child in English and bilateral cochlear implants. All children had a standardised baseline assessment that included demographics, hearing and medical history, communication history, language measures, cognitive tests, speech recognition, an audiological exam, psychosocial assessment including parent-child videotapes and parent reported quality of life. Follow-up visits are scheduled at six-month intervals and include a standardised assessment of the full battery of measures. Quality assurance activities were incorporated into the design of the study. A total of 188 CI children and 97 NH peers were enrolled between November 2002 and December 2004. The mean age, gender and race of the CI and NH children are comparable. With regard to parental demographics, the CI and NH children's families are statistically different. The parents of CI children are younger, and not as well educated, with 49% of CI parents reporting college graduation vs. 84% of the NH parents. The income of the CI parents is also lower than the NH parents. Assessments of cognition suggest that there may be baseline differences between the CI and NH children; however the scores were high enough to suggest language learning potential. The observed group differences identified these baseline characteristics as potential confounders which may require adjustment in analyses of outcomes. This longitudinal cohort study addresses questions related to high variability in language outcomes. Identifying sources of that variance requires research designs that: characterise potential predictors with accuracy, use samples that adequately power a study, and employ controls and approaches to analysis that limit bias and error. The CDaCI study was designed to generate a more complete picture of the interactive processes of language learning after implantation.

Effects of cochlear implant use on the electrically evoked middle latency response in children

The electrically evoked middle latency response (eMLR) reflects central auditory activity in cochlear implant users. This response was recorded repeatedly in 50 children over the first year of cochlear implant use and in 31 children with 5.3+/-2.9 years of implant experience. The eMLR was rarely detected at the time of implantation in anaesthetized or sedated children and was detected in only 35% of awake children at initial device stimulation. The detectability of the eMLR increased over the first year of implant use becoming 100% detectable in children after at least one year. Acutely evoked responses were more likely to be present in older children despite longer periods of auditory deprivation. Within six months of implant use, most children had detectable eMLRs. At early stages of device use, eMLR amplitudes were lower in children implanted below the age of 5 years compared to children implanted at older ages; amplitudes increased over time in both groups. Latencies after six months of implant use were prolonged in the younger group and decreased with implant use. EMLR changes with chronic cochlear implant use suggest an activity-dependent plasticity of the central auditory system. Results suggest that the pattern of electrically evoked activity and development in the auditory thalamocortical pathways will be dependent upon the duration of auditory deprivation occurring in early childhood.

Cochlear implants in young children

The cochlear implant is best characterized as a device that provides access to the sound environment. The device enables the hearing pathway to respond to environmental and speech sounds, providing informational cues from the surroundings and from others that may escape visual detection. As the developmental effects of a profound hearing loss are multiple, cochlear implants have been applied to ever younger children in an attempt to promote a more normal level of developmental learning through audition. In deafness, transducer elements of the inner ear fail to trigger auditory nerve afferent nerves in the presence of sound input. However, large reserves of afferent fibers exist even in the auditory nerve of a profoundly deaf patient. Furthermore, these nerve fibers retain the ability to respond to prosthetic activation. Through developmental learning in the early, formative years, auditory centers of the brain appear capable of processing information from the implant to provide speech comprehension and oral language development. Multichannel implants have replaced original single channel designs. multichannel devices enable larger percentages of recipients to recognize the spoken word without visual cues because they provide spectral information in addition to temporal and intensity cues. Testing under conditions of auditory (implant)-only input reveals significant open-set speech understanding capabilities in more than 75% of children after three years of device use. The benefit provided by implants may vary with a number of conditions including: hearing history, age of deafness onset, age at implantation, etiology of deafness, linguistic abilities, and the presence of a motivated system of support of oral language development. Patient variables should be given individual consideration in judging candidacy for a cochlear implant and in planning rehabilitative and education services after surgery and activation of the device.

Background and educational characteristics of prelingually deaf children implanted by five years of age

PURPOSE

This study documents child, family and educational characteristics of a large representative sample of 8- to 9-yr-old prelingually deaf children who received a cochlear implant by 5 yr of age. Because pre-existing factors such as the child's gender, family characteristics, additional handicaps, age at onset of deafness and at implant, may affect postimplant outcomes, these variables must be accounted for before the impact of educational factors on performance with an implant can be adequately determined. Classroom variables that may affect postimplant outcomes include placement in public or private, mainstream or special education, oral or total communication environments. Other intervention variables include type and amount of individual therapy, experience of the therapist and parent participation in therapy. Documenting these characteristics for a large representative sample of implanted children can provide clinicians and researchers with insight regarding the types of families who sought early cochlear implantation for their children and the types of educational programs in which they placed their children after implantation. It is important to undertake studies that control for as many of these factors as possible so that the relative benefits of specific educational approaches for helping children to get the most benefit from their cochlear implant can be identified.

METHOD

Over a 4-yr period, 181 children from across the US and Canada, accompanied by a parent, attended a cochlear implant research camp. Parents completed questionnaires in which they reported the child's medical and educational history, characteristics of the family, and their participation in the child's therapy. The parent listed names and addresses of clinicians who had provided individual speech/language therapy to the child and signed permission for these clinicians to complete questionnaires describing this therapy.

RESULTS

To the extent that this sample is representative of those families seeking a cochlear implant for their child, especially during the initial period of device availability, this population can be characterized as follows. Most parents had normal hearing, were of majority (white) ethnicity and had more education and higher incomes than the general population. The families tended to be intact with both a mother and a father who involved their hearing-impaired child in family activities on a regular basis. The children were enrolled in the full range of educational placements available across the United States and Canada. Fairly even distributions of children from public and private schools, special education and mainstream classes and oral and total communication methodologies were represented. Educational placement changed as children gained increased experience with a cochlear implant. They received an increased emphasis on speech and auditory skills in their classroom settings and tended to move from private school and special education settings to public school and mainstream programs. These data support the position that early cochlear implantation is a cost effective procedure that allows deaf children to participate in a normal school environment with hearing age mates.

Factors Affecting the Development of Speech, Language, and Literacy in Children With Early Cochlear Implantation

PURPOSE

This study investigated factors contributing to auditory, speech, language, and reading outcomes in children with prelingual deafness after 4-6 years of multichannel cochlear implant use. The analysis controlled for the effects of child, family, and implant characteristics so that educational factors most conducive to maximum implant benefit could be identified.

METHOD

The sample included 136 8- and 9-year-old children from across the United States and Canada who were implanted by age 5 with the Nucleus 22-channel implant. Type and amount of educational intervention since implantation constituted the independent variables. The dependent variable was performance on a battery of tests of speech perception, speech production, language, and reading administered 4-6 years postimplant. Characteristics of the child, the family, and the implant itself constituted intervening variables. A series of multiple regression analyses determined the amount of variance in each outcome accounted for by the intervening variables and the amount of additional variance attributable to independent variables.

RESULTS

Characteristics of the child and the family (primarily nonverbal IQ) accounted for approximately 20% of the variance in postimplant outcome. An additional 24% was accounted for by implant characteristics and 12% by educational variables, particularly oral communication mode.

CLINICAL IMPLICATIONS

Auditory, speech, language, and reading skills achieved 4-6 years after cochlear implantation were most strongly associated with nonverbal IQ, implant functioning, and use of an oral communication mode.

School-Based Services for Children With Cochlear Implants

School-based speech, language, and hearing professionals are instrumental in the provision of rehabilitative, consultative, and support services for children with cochlear implants. This article reviews current candidacy requirements as well as factors that are considered when a child is evaluated for a cochlear implant. Following implantation, school professionals play a pivotal role in providing an appropriate educational program that should include auditory training and the integration of listening into the child’s daily routine. The article presents procedures for maintaining and troubleshooting the device, and suggestions for establishing routines for device use and for improving the listening environment for children in classrooms.

Influence of age at implantation and of residual hearing on speech outcome measures after cochlear implantation: binary partitioning analysis

The goal of this study was to evaluate speech understanding outcomes in prelingually deaf children who use a cochlear implant device. Specifically, we discuss investigations on 2 prognostic variables--age at implantation and degree of residual hearing--and use a novel method: binary partitioning analysis. Our outcome measures are standard speech perception evaluations, including the Word Intelligibility by Picture Identification (WIPI) test, the Phonetically Balanced-Kindergarten (PBK) test, and the Glendonald Auditory Screening Procedure (GASP). Regarding age at implantation, we definitely showed that growth rates of speech understanding do relate to age at implantation, but not in a simple fashion. We used binary partitioning in an attempt to find the age at implantation that best separates the performances of children with younger versus older ages at implantation. We found that there is no one "critical age"; much appears to depend on the nature and difficulty (eg, whether open- or closed-set) of the test used. Regarding residual hearing, binary partitioning analysis was unable to show that the amount of residual hearing (as shown by preimplantation audiometric data) has any significant bearing on speech outcome measures in congenitally or prelingually deaf children.

Cochlear and brainstem implantation

Cochlear implantation is an established habilitative and rehabilitative option for profoundly deafened individuals over 1 year of age who derive limited benefit from conventional hearing aids. Auditory performance varies among individuals and is determined primarily by age at implantation, pre-existence of speech and language skills, and the time interval between onset of deafness and implantation. Successful implant users generally demonstrate improved auditory abilities and speech production skills beyond those achieved with hearing aids. Multichannel ABIs can provide useful auditory information to patients with NF-2 who have lost integrity of auditory nerves following removal of vestibular schwannomas. The implant allows for awareness of environmental sounds and, potentially, speech recognition. Most patients undergoing implantation demonstrate improved lip-reading skills, and exceptional performers achieve understanding of open-set speech.

The effects of chronic intracochlear electrical stimulation on inferior colliculus spatial representation in adult deafened cats

Previous studies have shown that chronic electrical stimulation through a cochlear implant causes significant alterations in the central auditory system of neonatally deafened cats. The goal of this study was to investigate the effects of chronic stimulation in the mature auditory system. Normal hearing adult animals were deafened by ototoxic drugs and received daily electrical stimulation over periods of 4-6 months. In terminal physiology experiments, response thresholds to pulsatile and sinusoidal signals were recorded within the inferior colliculus (IC). Using previously established methods, spatial tuning curves (STCs; threshold vs. IC depth functions) were constructed, and their widths measured to infer spatial selectivity. The IC spatial representations were similar for pulsatile and sinusoidal stimulation when phase duration was taken into consideration. However, sinusoidal signals consistently elicited much lower thresholds than pulsatile signals, a difference not solely attributable to differences in charge/phase. The average STC width was significantly broader in the adult deafened/stimulated animals than in controls (adult deafened/unstimulated cats), suggesting that electrical stimulation can induce spatial expansion of the IC representation of the chronically stimulated cochlear sector. Further, results in these adult animals were not significantly different from results in neonatally deafened, early stimulated animals, suggesting that a similar degree of plasticity was induced within the auditory midbrains of mature animals.

Cochlear implants and brain stem implants

This chapter describes the development of two implantable prosthetic neurostimulators which, in the last 20 years, have revolutionised the management of severe-to-profound sensorineural deafness. We have witnessed their rapid evolution from the realms of esoteric laboratory abstraction, with many critics and little perceived clinical use, to a routine treatment which is safe, effective and, indeed, cost effective. It is one of the great triumphs of biomedical and surgical collaboration, and is without any doubt the greatest ever advance in the treatment of deafness.

Functional differentiation of the auditory association area in prelingually deaf subjects

BACKGROUND

it is believed that the number of neurons of the human cortex increases rapidly in the first postnatal year, and then decreases gradually towards adult level as their functions are revised up to 11 years of age ('synaptic revision'). It is also confirmed that regional cerebral blood flow (rCBF) at rest represents the density of the neurons and decreases in accordance with the synaptic revision in process. If synaptic revision does not occur, rCBF remains at high level. Thus, we can evaluate whether functional differentiation has occurred in the human cortex by measuring rCBF at resting state.

OBJECTIVE

to examine functional differentiation of the auditory association area (A2) in prelingually deaf subjects.

METHODS

six postlingually and six prelingually deaf subjects who had undergone cochlear implant (CI) were involved in the current study. All prelingually deaf subjects underwent CI over 8 years old. The rCBF in A2 was examined during resting and listening to speech sounds using positron emission tomography (PET) and H2(15)O intravenous injection. Twelve normal subjects' rCBFs were also measured as control. Furthermore, three prelingually deaf subjects underwent follow up PET studies in which cortical activities in A2 for listening and lipreading were examined.

RESULTS

in the examination of rCBF at rest, rCBFs of prelingually deaf subjects in A2 showed significantly higher than those of either the postlingually deaf subjects or normal subjects. During listening, rCBFs in A2 increased in postlingually deaf subjects and normal subjects, while there was no significant rCBF increase in the prelingually deaf. High rCBF level in A2 at rest observed in prelingually deaf subjects implied a lack of synaptic revision, and it was suggested that the functional differentiation for auditory processing was little in the A2 of prelingually deaf subjects. In the follow up study for three prelingually deaf subjects, activation of A2 was observed during lipreading but not during listening in two cases, who had developed the skill of lipreading while speech recognition was not improved by CI. In contrast, the other case had not used any visual clues in daily communication prior to CI, and the hearing acuity was well improved by CI. This case demonstrated an activity in A2 during listening, while lipreading induced no activation.

CONCLUSION

it is suggested that functional differentiation of A2 should differ according to which of visual and auditory clue is chiefly used during critical periods for speech acquisition. The findings are thought to be important for us to schedule the education and treatment for prelingually deaf children.

Cognitive factors and cochlear implants: some thoughts on perception, learning, and memory in speech perception

Over the past few years, there has been increased interest in studying some of the cognitive factors that affect speech perception performance of cochlear implant patients. In this paper, I provide a brief theoretical overview of the fundamental assumptions of the information-processing approach to cognition and discuss the role of perception, learning, and memory in speech perception and spoken language processing. The information-processing framework provides researchers and clinicians with a new way to understand the time-course of perceptual and cognitive development and the relations between perception and production of spoken language. Directions for future research using this approach are discussed including the study of individual differences, predicting success with a cochlear implant from a set of cognitive measures of performance and developing new intervention strategies.

Meta-analysis of pediatric cochlear implant literature

We analyzed published reports of the effect of age at implantation and the cause of and age at onset of deafness on speech perception benefit in children with cochlear implants, and compared these results with those of unreported trials of multichannel cochlear implants. Combining data from published and unpublished patient series was constrained by differences in test protocols between studies, but was made feasible by employing a meta-analysis in which data were converted into an ordinal classification scale that represented levels of communicative benefit. Results showed that more rapid gains in speech perception are associated with earlier age at implantation, and that speech perception results are independent of cause of or age at onset of deafness after 1 year of implant use. Moreover, with minor exceptions, there was no statistical difference between published and unpublished data, thereby indicating no publication bias in the literature. A meta-analytic approach is useful because it can clarify the quality of reported data and the direction of future research and, hopefully, foster collaboration in conducting and reporting future research. A standardized approach to reporting results in children is advised in order to produce a balanced interpretation of implant benefit and to facilitate wider understanding and dissemination of study conclusions.

Sound-induced activation of auditory cortices in cochlear implant users with post- and prelingual deafness demonstrated by positron emission tomography

Changes of regional cerebral blood flow (rCBF) in the auditory cortices induced by sound stimulation were examined in nine postlingually and five prelingually deaf cochlear implant (CI) users by 15O-labeled water Positron Emission Tomography, and the results were compared with those of eight normal volunteers. Speech stimulation caused significantly greater rCBF increase compared with noise stimulation in the auditory association area in normal and postlingually deaf subjects. In prelingually deaf subjects, however, speech activation of the auditory association area was much less than that found in either of the other two groups. Neuronal networks for speech sound processing in the auditory association area in postlingually deaf individuals are thought be similar to those in normal subjects, while those in prelingually deaf patients who received CI after the speech acquisition period may not develop completely.

Cochlear implants in children

Cochlear implants allow the rehabilitation of children with severe to profound hearing loss. They are beneficial for not only postlingual children with hearing loss but also for children with congenital or prelingual hearing loss. Issues regarding cochlear implant candidacy and surgery are discussed. The results of cochlear implants in children and the complications related to cochlear implant surgery in children are reviewed.

Children who could benefit from a cochlear implant: a European estimate of projected numbers, cost and relevant characteristics

The incidence of profound hearing impairment by the age of 5, derived from a number of retrospective studies in the UK (population about 58 million; birth rate 14/1000), is estimated to be about 300 per annual birth cohort in the 1990s. This estimate includes 80 children who might be expected to acquire deafness in those first 5 years. Projected to Europe as a whole (population 511 million; birth rate 12/1000) this would mean a population who should be considered as potential cochlear implant patients of some 2268 children, given a variety of assumptions. At a take-up rate of 25% for both congenital and acquired cases of profound hearing impairment this would imply a European-wide expenditure of the order of 17 pounds m/p.a. on hardware and associated rehabilitation programmes. The need for such programmes is explored, in the context of strategies of early identification of hearing impairments.