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PubMed2003

Activity-dependent developmental plasticity of the auditory brain stem in children who use cochlear implants.

OBJECTIVES: 1) To determine if a period of early auditory deprivation influences neural activity patterns as revealed by human auditory brain stem potentials evoked by electrical stimulation from a cochlear implant. 2) To examine the potential for plasticity in the human auditory brain stem. Specifically, we asked if electrically evoked auditory potentials from the auditory nerve and brain stem in children show evidence of development as a result of implant use. 3) To assess whether a sensitive or critical period exists in auditory brain stem development. Specifically, is there an age of implantation after which there are no longer developmental changes in auditory brain stem activity as revealed by electrically evoked potentials? DESIGN: The electrically evoked compound potential of the auditory nerve (ECAP) and the electrically evoked auditory brain stem response (EABR) were recorded repeatedly during the first year of implant use in each of 50 children. The children all had pre- or peri-lingual onset of severe to profound sensorineural hearing loss and received their implants at ages ranging from 12 mo to 17 yr. All children received Nucleus cochlear implant devices. All children were in therapy and in school programs that emphasized listening and required the children to wear their implants consistently. RESULTS: Initial stimulation from the cochlear implant evoked clear responses from the auditory nerve and auditory brain stem in most children. There was no correlation between minimum latency, maximum amplitude, or slope of amplitude growth of initial responses with age at implantation for ECAP eN1, EABR eIII and eV components (p > 0.05). During the first year of implant use, minimum latency of these waves significantly decreased (p < 0.01, p < 0.0001, p < 0.0001, respectively). Neural conduction time, measured using the interwave latency of ECAP eN1-EABR eIII for lower brain stem and EABR eIII-eV for upper brain stem, decreased during the period of 6 to 12 mo of cochlear implant use (p < 0.01 (lower), p < 0.0001(upper)). The ECAP wave eN1 and the EABR wave eV showed significant increases in amplitude during time of implant use (p < 0.05 and p < 0.01, respectively). There were no correlations between the rate of interwave latency decrease and the rate of amplitude increases and the age at which children underwent implantation (p < 0.05). CONCLUSIONS: Activity in the auditory pathways to the level of the midbrain can be evoked by acute stimulation from a cochlear implant. EABR measures are not influenced by any period of auditory deprivation. Auditory development proceeds once the implant is activated and involves improvements in neural conduction velocity and neural synchrony. Underlying mechanisms likely include improvements in synaptic efficacy and possibly increased myelination. The developmental plasticity that we have shown in the human auditory brain stem does not appear from EABR data to be limited by a critical period during childhood.

Adolescent↗

PubMed2003

Speech perception of Mandarin Chinese speaking young children after cochlear implant use: effect of age at implantation.

OBJECTIVE: The purposes of this study were to examine (1). whether the benefit of cochlear implants in Mandarin-speaking congenitally deaf children persists over a 2-year follow-up period, and (2). whether the age of the child at implantation affects the acquisition of speech perception by young deafened children. METHOD: Sixteen congenitally deaf children received implants of Nucleus CI24M devices. Speech perception tests were conducted using the Mandarin Auditory Perception Test Battery at 6-month intervals after connection of the device. We determined the benefit of cochlear implants by monitoring percent correct scores between 12 and 24 months after implantation. Regression analysis was used to correlate the measures of progress and the age at implantation. RESULTS: In the comparison of performance at 12 and 24 months post-connection, subjects performed significantly better at 24 than at 12 months in spondee, vowel, and consonant tests (P<0.05). In phrase and sentence tests, the mean score improved over time with device use, but the difference was not significant (P=0.066 and 0.067, respectively). However, no obvious improvement in average score was found in tone tests (P=0.386). Progress (improvement in speech perception) at 12 and 24 months had moderate negative correlations with age at implantation in spondee, vowel, phrase and sentence tests (P<0.05), but no correlation with age in consonant (P=0.20) and tone tests (P=0.26). CONCLUSION: The result, in accordance with the reports on Western language-speaking children, showed cochlear implants increasingly benefit Mandarin-speaking congenitally deaf children over a 2-year post-implantation period. Because age at implantation negatively correlates with improved speech perception after implantation, congenitally affected children with profound deafness (if they cannot obtain enough benefit from hearing aids) should receive implants as early as possible.

Age Factors↗

PubMed2000

Speech perception in children with cochlear implants: effects of lexical difficulty, talker variability, and word length.

The present results demonstrated that all 3 factors --lexical difficulty, stimulus variability, and word length--significantly influenced spoken word recognition by children with multichannel cochlear implants. Lexically easy words were recognized significantly better than lexically hard words, regardless of talker condition or word length of the stimuli. These results support the earlier findings of Kirk et al(12) obtained with live-voice stimulus presentation and suggest that lexical effects are very robust. Despite the fact that listeners with cochlear implants receive a degraded speech signal, it appears that they organize and access words from memory relationally in the context of other words. The present results concerning talker variability contradict those previously reported in the literature for listeners with normal hearing(7,11) and for listeners with mild-to-moderate hearing loss who use hearing aids.(14) The previous investigators used talkers and word lists different from those used in the current study and found that word recognition declined as talker variability increased. In the current study, word recognition was better in the multiple-talker condition than in the single-talker condition. Kirk(15) reported similar results for postlingually deafened adults with cochlear implants who were tested on the recorded word lists used in the present study. Although the talkers were equally intelligible to listeners with normal hearing in the pilot study, they were not equally intelligible to children or adults with cochlear implants. It appears that either the man in the single-talker condition was particularly difficult to understand or that some of the talkers in the multiple-talker condition were particularly easy to understand. Despite the unexpected direction of the talker effects, the present results demonstrate that children with cochlear implants are sensitive to differences among talkers and that talker characteristics influence their spoken word recognition. We are conducting a study to assess the intelligibility of each of the 6 talkers to listeners with cochlear implants. Such studies should aid the development of equivalent testing conditions for listeners with cochlear implants. There are 2 possible reasons the children in the present study identified multisyllabic words better than monosyllabic words. First, they may use the linguistic redundancy cues in multisyllabic words to aid in spoken word recognition. Second, multisyllabic words come from relatively sparse lexical neighborhoods compared with monosyllabic tokens. That is, multisyllabic words have fewer phonetically similar words, or neighbors, competing for selection than do monosyllabic stimuli. These lexical characteristics most likely contribute to the differences in identification noted as a function of word length. The significant lexical and word length effects noted here may yield important diagnostic information about spoken word recognition by children with sensory aids. For example, children who can make relatively fine phonetic distinctions should demonstrate only small differences in the recognition of lexically easy versus hard words or of monosyllabic versus multisyllabic stimuli. In contrast, children who process speech using broad phonetic categories should show much larger differences. That is, they may not be able to accurately encode words in general or lexically hard words specifically. Further study is warranted to determine the interaction between spoken word recognition and individual word encoding strategies.

Child, Preschool↗

PubMed2002

Cochlear implants in young children.

The past 20 years have seen the cochlear implant evolve from an innovative but radical concept to the standard of care in the management of children with severe to profound hearing loss. All children receiving the cochlear implant achieve substantial benefit; however, performance gains are optimized by a team approach to the evaluation and management of these children. The critical elements of this team include audiologists, speech pathologists, and surgeons with specific interest, expertise, and dedication to the management of children with cochlear implants. Children are not well served by practitioners who delegate follow-up to educational programs not experienced in children with implants. Long-term involvement and dedication on the part of teachers, speech pathologists, audiologists, surgeons, and family are critical to maximizing the benefit the child receives.

Adolescent↗

PubMed2006

Simultaneous bilateral cochlear implantation in adults: a multicenter clinical study.

OBJECTIVE: To determine the efficacy of "simultaneous" bilateral cochlear implantation (both implants placed during a single surgical procedure) by comparing bilateral and unilateral implant use in a large number of adult subjects tested at multiple sites. DESIGN: Prospective study of 37 adults with postlinguistic onset of bilateral, severe to profound sensorineural hearing loss. Performance with the bilateral cochlear implants, using the same speech processor type and speech processing strategy, was compared with performance using the left implant alone and the right implant alone. Speech understanding in quiet (CNCs and HINT sentences) and in noise (BKB-SIN Test) were evaluated at several postactivation time intervals, with speech presented at 0 degrees azimuth, and noise at either 0 degrees , 90 degrees right, or 90 degrees left in the horizontal plane. APHAB questionnaire data were collected after each subject underwent a 3-wk "bilateral deprivation" period, during which they wore only the speech processor that produced the best score during unilateral testing, and also after a period of listening again with the bilateral implants. RESULTS: By 6-mo postactivation, a significant advantage for speech understanding in quiet was found in the bilateral listening mode compared with either unilateral listening modes. For speech understanding in noise, the largest and most robust bilateral benefit was when the subject was able to take advantage of the head shadow effect; i.e., results were significantly better for bilateral listening compared with the unilateral condition when the ear opposite to the side of the noise was added to create the bilateral condition. This bilateral benefit was seen on at least one of the two unilateral ear comparisons for nearly all (32/34) subjects. Bilateral benefit was also found for a few subjects in spatial configurations that evaluated binaural redundancy and binaural squelch effects. A subgroup of subjects who had asymmetrical unilateral implant performances were, overall, similar in performance to subjects with symmetrical hearing. The questionnaire data indicated that bilateral users perceive their own performance to be better with bilateral cochlear implants than when using a single device. CONCLUSIONS: Findings with a large patient group are in agreement with previous reports on smaller groups, showing that, overall, bilateral implantation offers the majority of patients advantages when listening in simulated adverse conditions.

Adult↗

PubMed2006

Telephone use: what benefit do cochlear implant users receive?

This study evaluated the use of landline and mobile phones in an international sample of cochlear implant users. A custom-designed survey was mailed to cochlear implant users from four different countries. A link to the survey was posted on the MED-EL website, with responses from a further six countries. Results from 196 surveys show that there is a significant shift from pre-operative non-use of a telephone to use of a telephone post-operatively. Seventy-one percent of MED-EL cochlear implant users are able to use a landline telephone to some extent and 54% are able to use a mobile phone to some extent. Talking to familiar speakers about familiar topics is the easiest listening condition on the telephone, and it is easier to recognize a voice using the landline. Many respondents found it difficult to make a call without some assistance. Most respondents could manage to call someone in an emergency, even on a mobile phone. Data obtained should provide useful information in the counselling and rehabilitation of cochlear implant recipients and candidates.

Adolescent↗

PubMed1995

Speech production changes with the Nucleus 22-channel cochlear implant.

The speech production changes of a postlingually deaf child and adult with a multichannel cochlear implant were spectrographically analyzed over a period of time. The segmental analysis in both case studies included the measurement of vowel, fricative, and plosive burst duration; first and second vowel formant frequency relationship; and centroid frequencies of fricatives and plosive bursts. The suprasegmental analysis in the second case study (adult) investigated sentence duration, pitch variation, and word stress. Results of both case studies indicated an overall improvement in the accuracy of consonant and vowel productions following the multichannel cochlear implant, in terms of duration, centroid frequencies, and vowel formant frequency relationships. The suprasegmental analysis indicated an overall improvement with the use of the cochlear implant over time. These positive changes in speech production may be indicative of the improved auditory feedback information provided by the cochlear implant.

Adult↗

PubMed2004

Relationship between cochlear implant outcome and the diameter of the cochlear nerve depicted on MRI.

This study aimed to evaluate the relationship between the diameters of the auditory and eighth cranial nerves and improvements in post-implant performance. Twenty prelingually deafened children (aged from 2.0 to 6.0 years) who received the Nucleus 24 cochlear implant participated in this study. All subjects had used their implant for at least 1 year after device connection. The diameters of cochlear and eighth cranial nerves were retrospectively measured on preoperative T2-weighted axial magnetic resonance image (MRI). In 17 of 20 subjects, the cochlear and eighth cranial nerves could be identified on MRI. The mean diameter of the cochlear and eighth cranial nerves were 0.9 +/- 0.2 mm and 1.2 +/- 0.3 mm, respectively. In the remaining three subjects, the cochlear and eighth cranial nerves could not be identified on MRI. These three subjects had significantly lower scores in the Infant-Toddler-Meaningful Auditory Integration Scale (IT-MAIS) than the other 17 subjects at 12 months post-implant. There was no significant correlation among the maximal diameters of the nerves and age, ECAP thresholds and IT-MAIS scores. A sufficient outcome from cochlear implantation can be expected when cochlear and eighth cranial nerves are depicted on MRI, regardless of the nerve diameters.

Analysis of Variance↗

PubMed2001

Loudness perception and late auditory evoked potentials in adult cochlear implant users.

In clinical routine the adjustment of speech processors in cochlear implant users is based on the patients' subjective statements about the loudness of specific electrical stimuli. From hearing patients it is known that the latencies and amplitudes of late auditory evoked potentials (LAEP) which are generated within the auditory cortex correlate with the loudness perception of acoustical stimuli. The aim of this study was to investigate the correlation between LAEP and loudness perception in adult cochlear implant users. We investigated 8 adult subjects who had been provided with a 22 electrode Cochlear Implant (nucleus CI24M) at least 6 months prior to the investigation. All subjects showed open speech understanding. Electrical pulse trains of 300 ms duration presented at a single electrode served as stimuli. Electrically LAEP morphologies were similar to normal hearing subjects. In all subjects and each intracochlear electrode position LAEP were well identifiable down to low loudness sensations. Both amplitudes and latencies depended on the loudness perception. The best correlation was observed for the N1 deflection. The results show that LAEP can be used for estimation of both hearing thresholds and most comfortable levels.

Adult↗

PubMed1996

Cost utility of the multichannel cochlear implants in 258 profoundly deaf individuals.

Cost utility analysis is a method of cost-effectiveness analysis which provides results in terms of cost per quality-adjusted life-year (QALY). Cost utility for the multichannel cochlear implant was calculated using Ontario Health Utilities Index data from 229 Nucleus 22-channel implant users and 32 cochlear implant candidates awaiting surgery. The health utility of the implanted group was greater than that of the candidate group by 0.204 (P<.0001). Use of this figure in a cost utility calculation indicates that cochlear implantation costs approximately $15,928 per QALY provided. Sensitivity analysis, a technique which systematically varies the assumptions underlying the calculations, suggests a range for the true value of between $12,000 and $30,000. This compares very favorably with other medical interventions. It is concluded that profound hearing loss has a significant effect on quality of life, and measurement of the changes that result from cochlear implant use indicates that this technology provides significant improvements and is quite cost-effective.

Aged↗

PubMed2000

Plasticity in central representations in the inferior colliculus induced by chronic single- vs. two-channel electrical stimulation by a cochlear implant after neonatal deafness.

The goal of this research is to examine the functional consequences of patterned electrical stimulation delivered by a cochlear implant in the deafened developing auditory system. In previous electrophysiological experiments conducted in the inferior colliculus (IC), we have demonstrated that the precise cochleotopic organization of the central nucleus (ICC) develops normally in neonatally deafened unstimulated cats and is unaltered despite the lack of normal auditory input during development. However, these studies also showed that chronic electrical stimulation delivered at a single intracochlear location by one bipolar channel of a cochlear implant induces significant expansion of the central representation of the stimulated cochlear sector and degrades the cochleotopic organization of the IC. This report presents additional data from a new experimental series of neonatally deafened cats that received chronic stimulation on two adjacent bipolar intracochlear channels of a cochlear implant. Results suggest that competing inputs elicited by electrical stimulation delivered by two adjacent channels can maintain the selective representations of each activated cochlear sector within the central auditory system and prevent the expansion seen after single-channel stimulation. Alternating stimulation of two channels and use of highly controlled electrical signals may be particularly effective in maintaining or even sharpening selectivity of central representations of stimulated cochlear sectors. In contrast, simultaneous stimulation using two channels of a model analog cochlear implant processor in one experimental animal failed to maintain channel selectivity and resulted in marked expansion and fusion of the central representations of the stimulated channels. This potentially important preliminary result suggests that under some conditions the central auditory system may be unable to discriminate simultaneous, overlapping inputs from adjacent cochlear implant channels as distinct.

Animals↗

PubMed2004

Enhancing Chinese tone recognition by manipulating amplitude envelope: implications for cochlear implants.

Tone recognition is important for speech understanding in tonal languages such as Mandarin Chinese. Cochlear implant patients are able to perceive some tonal information by using temporal cues such as periodicity-related amplitude fluctuations and similarities between the fundamental frequency (F0) contour and the amplitude envelope. The present study investigates whether modifying the amplitude envelope to better resemble the F0 contour can further improve tone recognition in multichannel cochlear implants. Chinese tone and vowel recognition were measured for six native Chinese normal-hearing subjects listening to a simulation of a four-channel cochlear implant speech processor with and without amplitude envelope enhancement. Two algorithms were proposed to modify the amplitude envelope to more closely resemble the F0 contour. In the first algorithm, the amplitude envelope as well as the modulation depth of periodicity fluctuations was adjusted for each spectral channel. In the second algorithm, the overall amplitude envelope was adjusted before multichannel speech processing, thus reducing any local distortions to the speech spectral envelope. The results showed that both algorithms significantly improved Chinese tone recognition. By adjusting the overall amplitude envelope to match the F0 contour before multichannel processing, vowel recognition was better preserved and less speech-processing computation was required. The results suggest that modifying the amplitude envelope to more closely resemble the F0 contour may be a useful approach toward improving Chinese-speaking cochlear implant patients' tone recognition.

Adult↗

PubMed1997

Performance over time of adult patients using the Ineraid or nucleus cochlear implant.

This study examined the average and individual performance over time of 49 adult cochlear implant subjects. Subjects were randomly assigned to receive either the Ineraid cochlear implant, with analog processing, or the Nucleus cochlear implant, with feature-extraction processing. All subjects had postlingual profound bilateral sensorineural hearing loss and received no significant benefit from hearing aids before implantation. Group data were examined in two ways. First, only subjects who had complete data over the test period were examined. Second, an analysis of all available data was carried out by mixed linear-model analysis. In this analysis, to account for missed follow-ups at the planned intervals, data consisting of the observations closest in time to the planned test times were modeled by natural splines with knots at the planned follow-up times. Contrasts between all pairs of planned follow-up times for each device were tested, as were contrasts between devices at each planned follow-up time. Results indicated little difference between the performance of the Ineraid and Nucleus subjects in their level of performance or their rate of learning. Postimplantation performance was typically superior to preimplantation performance within 9 months, and continued to improve up to 18-30 months depending on the speech perception measure. In some subjects, improvements in speech perception measures were observed up to four or five years postimplantation. There was also evidence that three subjects had a decrement in overall speech perception performance, although their postimplantation scores were always higher than their preimplantation scores. In at least one subjects this was likely a result of age-related cognition decrements.

Adult↗

PubMed1998

Can event-related potentials be evoked by extra-cochlear stimulation and used for selection purposes in cochlear implantation?

To investigate whether electrically evoked event-related responses (P300) could be elicited by extra-cochlear stimulation, measurements were performed on a group of adults fitted with the single-channel extra-cochlear implant. To optimize measurement conditions, and because of the low number of subjects still using an extra-cochlear device in our cochlear implant programme, measurements were also performed on a group of experienced users fitted with the intra-cochlear Nucleus multichannel device. For reference purposes, subjects with normal hearing (control group) were also included in the study. Reproducible late latency responses (N1 and P2 peaks) were found in the five extra-cochlear implant users, while P300s were present in four out of these five subjects. The latencies were longer than those of the control group, but were similar to those obtained in the intra-cochlear implant group. Significant correlations were found for most N1, P2 and P300 measurements evoked by the tonal stimuli and by speech stimuli. The P300 amplitudes, evoked by either tonal or speech stimuli, appeared to be related to speech perception ability. This led to the conclusion that N1, P2 and P300 measurements may have potential as a clinical tool for preoperative prediction and postoperative evaluation of sound processing on a cortical level.

Adolescent↗

PubMed2004

Averaged electrode voltage testing to diagnose an unusual cochlear implant internal device failure.

This paper describes an unusual Clarion 1.2 cochlear implant failure in order to demonstrate the need for the clinical availability of electrode voltage testing. The case report describes a patient with a Clarion 1.2 cochlear implant who exhibited poor auditory progress in spite of grossly normal impedances and electric field testing, and an appropriate educational and psychosocial environment. For a subset of electrodes, however, electrode voltage testing was abnormal. At explantation it was found that the epoxy that protects the connection between the electrode leads of the array and the output contacts on the internal controller had fractured. This failure was not associated with reported head trauma. This case report demonstrates the utility of and clinical need for electrode voltage testing as a helpful tool to diagnose internal device failure.

Child, Preschool↗

PubMed2003

[Cochlear implants in adults: indications and realization. Special cases and technical parameters of the implantation systems].

From the technical point of view, cochlear implant (CI) surgery in adults is a well established procedure. Pre- and postoperative evaluation, surgical approach and rehabilitation programs are standardized, presenting CI as a low risk procedure with rare complications similar to those of middle ear surgery. Part 1 described the diagnostics, surgical procedure and possible complications. The second part will cover the contraindications, special cases as well as the technical parameters of the modern implant system.

Adult↗

PubMed1993

Psychophysical and speech perception studies: a case report on a binaural cochlear implant subject.

Further improvements in speech perception for cochlear implant patients in quiet and in noise should be possible with speech processing strategies using binaural implants. For this reason, presented here is a series of initial psychophysical and speech perception studies on the authors' first binaural cochlear implant patient. For an approximate matching of the places of stimulation on the two sides, the patient usually reported a single percept when the two sides were simultaneously stimulated. Lateralization was strongly influenced by amplitude differences between the electrical stimuli on the two sides, but only weakly by interaural time delays. Speech testing, comparing monaural with binaural electrical stimulation, showed a binaural advantage particularly in noise.

Adult↗

PubMed2004

Cochlear implantation in patients with a history of chronic otitis media.

OBJECTIVE: To propose management options for cochlear implantation in chronic otitis media based on our experiences. MATERIAL AND METHODS: A retrospective review of 418 cochlear implantations performed by the 2 senior authors between November 1988 and February 2004 was conducted. Nine patients who had chronic otitis media in the ear to be implanted were included. Of these, three showed active inflammation at presentation; the other six cases had undergone previous tympanomastoidectomy surgery and did not show active inflammation at presentation. RESULTS: Five patients with active inflammation or without an adequate soft tissue layer in the mastoid bowl underwent a two-stage procedure. Four cases who showed inactive inflammation and had an adequate tissue layer to protect the electrode array underwent a single-stage technique, although two of them showed dry tympanic membrane perforation. No local or intracranial inflammation recurred. The electrode was exposed in the mastoid bowl in one case, who was managed with revisional mastoid obliteration with soft tissue. CONCLUSION: Complete eradication of inflammation and the securing of a strong protective soft tissue layer over the electrode are prerequisites for cochlear implantation in ears with chronic otitis media.

Adult↗