Blood flow measurements in the ears of patients receiving cochlear implants

We measured cochlear blood flow in 12 patients who received cochlear implants, using a laser-Doppler probe with an outer diameter of 0.8 mm. The subjects had congenital deafness, idiopathic progressive sensorineural hearing loss, Waardenburg's syndrome, narrow internal auditory canal, or sudden deafness. Putting the probe tip to the site of drilling for cochlear implantation, we measured blood flow before, during, and after the cochlear bony wall was opened. The laser-Doppler output was confirmed even after the tip of the probe was inserted into the perilymphatic space in all cases. Our results revealed that blood flow was maintained in all cochleas, although there was a probability of reduction in blood flow volume. We conclude that laser-Doppler flowmetry is both relatively safe and useful for measuring blood flow in the ears during cochlear implantation procedures.

Speech perception in nucleus CI24M cochlear implant users with processor settings based on electrically evoked compound action potential thresholds

Adjusting the speech processor of a cochlear implant, per electrode, to the individual's response is a laborious task that may interfere with a user-friendly start of implant-mediated hearing, particularly in children. This research concerns the possibility of processor adjustment based on a profile derived from measurements of the electrically evoked compound action potential (ECAP) thresholds across the electrode array, followed by adjustment of the overall level of the profile to the hearing threshold and maximum comfortable loudness level using live voice. The results for CVC word lists show that speech perception is quite insensitive to the threshold setting of the speech processor. On average, the speech score does not decrease by more than 10% when, with the new method, the threshold setting comes out so much lower that the dynamic range has doubled. In contrast, the speech score appears to be sensitive to an increase of the maximum high-frequency stimulation settings for the basal electrodes, resulting in lower scores at these higher settings. The correlation between the overall ECAP thresholds and conventionally measured subjective thresholds is weak (r = 0.64). However, the correlation between the slopes of these threshold curves is satisfactory (r = 0.82). The correlation between the ECAP thresholds and the maximum stimulation levels is poor, both with respect to overall level and slope (r = 0.39 and 0.36, respectively). Applicability of the ECAP threshold in processor adjustment could not be demonstrated in this study. Prediction of the most critical factor in speech perception, the slope of the maximum stimulation curve, from the ECAP thresholds is poor. However, considering habituation to the initial processor setting of at least 6 months, the small decrease in the CVC scores with the new setting suggests that a more user-friendly adjustment procedure can be developed.

[Binaural cochlear implantation: general concept, surgical technique and electrophysiology]

Cochlear implant have been proven to be safe and cost-effective in deafened adults. Generally, a single cochlear implants is proposed providing monaural audition. Some teams have published interesting results in patients wearing two cochlear implants. The cost of the surgical procedure is greatly increased for bilateral implantation. In an attempt to provide patients with binaural hearing and a better chance to improve their capacity for frequency discrimination without an excessive increase in cost, we developed an new concept and design for binaural cochlear implants. The aim of the present study was to establish the surgical technique for binaural cochlear implantation with a single internal receptor-stimulator. We report descriptive data on surgical procedures performed in two cadavers and in two deafened adults. The special implant is composed of a single receptor-stimulator and two electrode arrays: a short one implanted into the ipsilateral ear and a long one in the contralateral ear. A specially designed tool for endoscopic facial lifting was used to create subcutaneous tunnels from the ipsilateral to the contralateral ear. Insertion into cochleas was unremarkable. Additional time for surgery (compared with mean operative time for routine adult surgery in our unit), and surgical details are discussed. Binaural cochlear implantation is feasible, easy and not very time consuming. Studies are in progress to determine patient benefit. Obtaining auditory brainstem evoked potentials electrically in patients with binaural cochlear implants is possible and provides an interesting mode for in vivo analysis of the long-term effect of profound/total deafness on neural transmission. In our patients, results have demonstrated that neural response properties in auditory pathways are negatively related to duration of deafness.

Perceptual learning following changes in the frequency-to-electrode assignment with the Nucleus-22 cochlear implant

The goal of the present study was to investigate the time course of adaptation by experienced cochlear implant users to a shifted frequency-to-electrode assignment in their speech processors. Speech recognition performance of three Nucleus-22 cochlear implant users was measured over a 3-month period, during which the implant listeners continuously wore "experimental" speech processors that were purposely shifted by 2-4 mm in terms of the frequency-to-electrode assignment relative to their normal processor. Baseline speech performance was measured with each subject's clinically assigned speech processor just prior to implementation of the experimental processor. Baseline speech performance was measured again after the 3-month test period, immediately following the reinstallation of the clinically assigned processor settings. Speech performance with the experimental processor was measured four times during the first week, and weekly thereafter over the 3-month period. Results showed that the experimental processor produced significantly lower performance on all measures of speech recognition immediately following implementation. Over the 3-month test period, consonant and HINT sentence recognition with the experimental processors gradually approached a performance level comparable to but still significantly below the baseline and postexperiment measures made with the clinically assigned processor. However, vowel and TIMIT sentence recognition with the experimental processors remained far below the level of the baseline measures even at the end of the 3-month experimental period. There was no significant change in performance with the clinically assigned processor before or after fitting with the experimental processor. The results suggest that a long-time exposure to a new pattern of stimulation may not be able to compensate for the deficit in performance caused by a 2-4-mm shift in the tonotopic location of stimulation, at least within a 3-month period.

Cochlear implantation without mastoidectomy: the pericanal electrode insertion technique

OBJECTIVE

A new minimally invasive cochlear implantation method with direct electrode insertion through the external auditory canal (EAC) is presented.

MATERIAL AND METHODS

Surgery begins with a retroauricular skin incision. The bony surface of the mastoid plane behind the ear is dissected free and the skin of the EAC is elevated together with the posterior part of the tympanic membrane. Cochleostomy is performed through the EAC with a microdrill anterior to the round window. A rim is drilled into the postero-superior region of the bony EAC immediately above the incus towards the outer border of the EAC and connected to the retroauricular surface by a short tunnel. The implant device is placed in the usual retroauricular area. The electrode is inserted through the tunnel and rim into the tympanic cavity and pushed into the cochleostomy hole. The electrode is immobilized in the rim using glass ionomer cement and covered with bone dust. After placement of the ground electrode, the retroauricular incision is closed. The tympano-meatal flap is replaced and a dressing is put into the EAC.

RESULTS

The new method has been applied thus far in 15 adults and pre-adolescent deaf patients (8 females, 7 males). A MED-EL Combi 40 + device was used in 14 patients and a Nucleus CI24M in 1. Pericanal electrode insertion was easy, with insertion depths into the cochlea of > or = 30 mm with the MED-EL and of 20 mm with the Nucleus device. There were no surgical complications, infections or electrode extrusions during postoperative observation periods ranging from 6 months to > 2 years. The functional results were comparable to those obtained with cochlear implantation via mastoidectomy. The pericanal electrode insertion technique has several advantages, the most important being that the danger of facial nerve damage is minimized and that the operating time is reduced by up to 50%.

CONCLUSION

Cochlear implantation with pericanal electrode insertion is a simple, fast and particularly safe option which may replace the classical transmastoidal cochlear implantation method in adults and older children.

[Bioethical issues in pediatric cochlear implants]

The use of cochlear implants can modify significantly the way in which deaf children relate with the outside world through psychological, linguistic and cognitive changes. The main question about this subject is the ethical controversy with regards to who has the right to make such a decision for a young child. We present the children evaluated at our hospital in order to assess the cochlear implant option. That population was of 37 implanted children, 10 children waiting for surgery and 21 rejected children. We describe and analyze from the bioethical bases and methodology the problems found: decision of no implant in children of hearing parents, the deaf culture point of view, the mature minor doctrine, teenagers, social and cultural problems, multihandicapped children and responsibility of the implants team.

Changes in speech production in a child with a cochlear implant: acoustic and kinematic evidence

A method is presented for examining change in motor patterns used to produce linguistic contrasts. In this case study, the method is applied to a child receiving new auditory input following cochlear implantation. This child experienced hearing loss at age 3 years and received a multichannel cochlear implant at age 7 years. Data collection points occurred both pre- and postimplant and included acoustic and kinematic analyses. Overall, this child's speech output was transcribed as accurate across the pre- and postimplant periods. Postimplant, with the onset of new auditory experience, acoustic durations showed a predictable maturational change, usually decreasing in duration. Conversely, the spatiotemporal stability of speech movements initially became more variable postimplantation. The auditory perturbations experienced by this child during development led to changes in the physiological underpinnings of speech production, even when speech output was perceived as accurate.

Recognition of lexically controlled words and sentences by children with normal hearing and children with cochlear implants

OBJECTIVE

The purpose of this study was to investigate the combined lexical effects of word frequency and neighborhood density (acoustic-phonetic similarity) on the recognition of words spoken in isolation and words spoken in sentences for children with normal hearing and children with cochlear implants.

DESIGN

Lexically controlled sentences were created from a subset of words obtained from the spoken vocabulary of children between the ages of 3 and 5 yr. Two sentence lists were generated, applying the definitions and procedures of Kirk, Pisoni, and Osberger (1995) in accordance with the Neighborhood Activation Model ( Luce, 1986; Luce & Pisoni, 1998). One list was composed of lexically "easy" words (those high in frequency of occurrence but phonemically dissimilar to other words) and the other list was composed of lexically "hard" words (those low in frequency of occurrence but phonemically similar to other words). Each list consisted of five practice and 20 test sentences that were syntactically correct but semantically neutral (low in predictability). Three key words were used in constructing each of the 5- to 7-word sentences, resulting in 15 practice and 60 key words per test list. In the first of three experiments, 48 normal-hearing children between the ages of 5 and 12 yr were asked to repeat the words and sentences at one of six presentation levels to establish performance-intensity functions. In the second experiment, 12 normal-hearing children between the ages of 5 and 14 yr repeated the words and sentences under spectrally degraded conditions. Twelve children with cochlear implants ages 5 to 14 yr repeated the unprocessed stimuli in a third experiment.

RESULTS

The lexically easy stimuli were recognized with greater accuracy than the lexically hard stimuli for the children tested in all three experiments. Sentence scores were significantly higher than word scores for the normal-hearing children (Experiments 1 and 2) and nine high-performing children with cochlear implants (Experiment 3). Word scores were higher than sentence scores for the three low-performing children with cochlear implants. There was a statistically significant relationship between chronological age and sentence score for the normal-hearing children listening under spectrally degraded conditions. For the children with cochlear implants, the relationship between language quotient and sentence and word scores was statistically significant.

CONCLUSION

Sensitivity to the combined lexical properties of word frequency and neighborhood density was evident both for words and sentences. Lexically easy stimuli were recognized with greater accuracy than lexically hard stimuli across groups, affirming the robustness of this effect and verifying that words were being organized in relation to the frequency and acoustic-phonetic properties of other words. Syntactic context facilitated word recognition for the children with normal hearing and the high-performing implant group. The three low-performing children with cochlear implants recognized words more accurately than sentences, reflecting limitations in linguistic and cognitive capacity.

Cochlear implantation in children with inner ear malformations: report of two cases

Cochlear implantation of congenitally deaf children with inner ear malformations is gaining special interest. Although the number of the reported cases is increasing, the decision for implantation needs thorough investigation. Preoperative evaluation, surgical approach and postoperative follow-up can be challenging.

STUDY DESIGN

A retrospective analysis of two cases with inner ear malformations.

PATIENTS

One patient was a 3-year-old-girl who had cochlear and cochleovestibular nerve aplasia on the left side and incomplete partition on the other side. The other patient was a 5-year-old-boy who had hypoplastic cochlea on both sides. Both of them also had vestibular anomalies. Cases were implanted by using multichannel cochlear implant.

RESULTS

No complications were encountered. Both patients responded to acoustic stimuli, and their speech perception skills were improved. After 10 months of cochlear implant use, their results seem encouraging.

CONCLUSION

Except cochlear or cochleovestibular nerve agenesis, inner ear malformations cannot be accepted as a contraindication for cochlear implantation. Although there can be difficulties during the surgery or in the postoperative period, patients with inner ear malformations can also benefit from cochlear implantation. It is essential that all possible complications and postoperative performance should be discussed with the parents.

Comparison of electrically evoked whole-nerve action potential and electrically evoked auditory brainstem response thresholds in nucleus CI24R cochlear implant recipients

In this study, differences between electrically evoked whole-nerve action potential (EAP) and electrically evoked auditory brainstem response (EABR) measurements within Nucleus CI24R cochlear implant recipients were evaluated. Precurved modiolus-hugging internal electrode arrays, such as the CI24R, are designed to provide more direct stimulation of neural elements of the modiolus. If the electrode array is closer to the modiolus, electrically evoked and behavioral levels might be lower than were previously recorded for the straight electrode array, the CI24M. EAP and EABR growth functions and behavioral levels were obtained for 10 postlingually deafened adults. Results revealed no significant differences between EAP and EABR threshold levels, and these levels were not significantly lower than those obtained using the CI24M.

Cochlear implantation for adolescents and adults with prelinguistic deafness

OBJECTIVE

Previous studies have suggested that individuals with long-term prelinguistic deafness who receive cochlear implants show little improvement in speech recognition skills. The purpose of this study was to examine the auditory functioning of individuals with prelinguistic deafness who received cochlear implants after the age of 12.

STUDY DESIGN AND SETTING

A retrospective study of open-set speech recognition was undertaken for 15 patients (adolescents and adults) with prelinguistic deafness who underwent implantation in the Ottawa Cochlear Implant Program. The results of open-set speech perception tests, both words and sentences, were reviewed to assess auditory functioning after implantation. Qualitative data using the Performance Inventory for Profound and Severe Loss questionnaire were also collected for the adults.

RESULTS AND DISCUSSION

The results of this study indicate that individuals with long-term prelinguistic deafness can achieve significant open-set speech understanding with a cochlear implant, although there is a wide range of performance across patients. The results ranged from 0% to 74% for words and 0% to 98% for sentences.

Cost-benefit analysis of pediatric cochlear implantation: German experience

HYPOTHESIS

To explore, from the payers' perspective, the cost-benefit ratio of pediatric cochlear implantation for congenitally deaf and prelingually deafened children compared with children with hearing aids. The study should verify the hypothesis that educational and associated costs increase with age at implantation and that these can be below costs for children with hearing aids.

METHODS

Children who received implants at the Medical University of Hanover at different ages (Group 1, 0-1.9 yr; Group 2, 2-3.9 yr; Group 3, 4-6.9 yr) were compared with deaf children using hearing aids (Group 4). Sick funds were the payers for direct and indirect costs, and public authorities were the payers for educational costs. Educational settings were used to measure for benefits. All costs related to the hearing deficiency were included up to the age of 16 years on the basis of 1999 currency values. A scenario analysis was used to explore the impact of variation of costs and discount rates.

RESULTS

Total costs for the three age groups of children with implants were from euro 138,000 (approximately US$113,100) to euro 177,000 (approximately US$152,700), compared with euro 160,000 (approximately US$138,000) for hearing aid users.

CONCLUSION

This study supports the view that pediatric cochlear implantation provides positive cost-benefit ratios compared with hearing aid users, depending on the age at implantation. Implantation is strongly recommended from the payers' perspective for children implanted before the age of 2 years.

The nucleus contour electrode array: an electrophysiological study

OBJECTIVE/HYPOTHESIS

Positioning intracochlear electrodes adjacent to the modiolus would lead to a reduction in threshold levels and latencies, as measured with electrically evoked auditory brainstems responses. Recently, Cochlear Corporation introduced a new perimodiolar array (Contour electrode) characterized by a platinum stylet inserted into the array's silicone carrier that keeps the electrode in a straightened configuration before insertion. After completion of the insertion, the withdrawal of the stylet allows the array to coil within the cochlea positioning electrodes closer to the modiolus. The purpose of the study was to analyze the stimulation properties of the Contour electrode by evaluating the effects of the withdrawal of the stylet on electrical auditory brainstem response (EABR) characteristics.

METHODS

Electrical auditory brainstem response registrations were performed intraoperatively on three electrodes (1 apical, 1 medial, 1 basal) before and after the removal of the stylet in 10 patients implanted with the Nucleus 24 Contour device. A within-patient comparison of EABR characteristics was performed. The Student test was used to assess differences in EABR measures obtained before and after the stylet removal.

RESULTS

Mean EABR thresholds were significantly lower after the removal of the stylet than with the stylet in situ for all three electrodes tested. After the removal of the stylet, latencies of waves III and V significantly decreased, whereas amplitudes significantly increased.

CONCLUSION

Reduction in EABR threshold levels and latencies as well as an increase in waves III and V amplitudes after the stylet removal all demonstrate the effectiveness of the Contour system in positioning intracochlear electrodes closer to auditory neurons.

The binaural digisonic cochlear implant: surgical technique

The surgical technique of cochlear implantation is currently well established. It is sure and efficient. The results of the cochlear implant concerning speech perception are good and have a favorable cost/efficiency ratio. However, some points remain to be researched. Bilateral implantation allows one to obtain a binaural perception and especially to increase, theoretically, the possibilities of frequency discrimination by reducing interactions between electrodes and therefore improving the patient's performance. Nevertheless, it seems important to caution against placing two implants in one patient, especially for economic reasons. Thus, we have developed, with the MXM Company, a concept of a unique implant able to stimulate both cochleas with a single processor and a single receiver: the Binaural Digisonic cochlear implant. This article describes the Binaural Digisonic system, the surgical technique as developed by postmortem dissection, and the first two implantations in patients.

Hearing restoration with auditory brainstem implant in three children with cochlear nerve aplasia

OBJECTIVE

To verify the possibility of auditory habilitation in children with aplasia and hypoplasia of the cochlear nerve by direct electrical stimulation of the cochlear nuclei with an auditory brainstem implant.

STUDY DESIGN

Retrospective case review.

SETTING

Study conducted at the Ear, Nose, and Throat Department of the University of Verona, Italy.

PATIENTS

Three children, aged 4, 3, and 2 years, respectively, with severe bilateral cochlear malformations and cochlear nerve aplasia have received an auditory brainstem implant at this institution in the past 2 years.

INTERVENTION

The classic retrosigmoid approach was used. Correct positioning of the electrodes was evaluated using electric auditory brainstem responses and neural response telemetry. Before the patients were discharged, high-resolution computed tomography with a bone algorithm reconstruction technique was performed to evaluate electrode placement. The auditory brainstem implant was activated 30 to 60 days after implantation.

RESULTS

No postoperative complications were observed. To date, 21, 18, and 8 electrodes, respectively, have been activated in the three children. The first patient, 12 months after activation, had achieved good environmental sound awareness, good speech detection, and some speech recognition. The second child, 8 months after activation, had achieved good environmental sound awareness and moderate speech detection. The third patient, 1 month after activation, had obtained good environmental sound awareness.

CONCLUSION

This study indicates that auditory brainstem implantation is technically feasible in children with cochlear nerve aplasia. The early results suggest the possibility of achieving auditory habilitation with auditory brainstem implantation in this population.

CT-derived estimation of cochlear morphology and electrode array position in relation to word recognition in Nucleus-22 recipients

This study extended the findings of Ketten et al. [Ann. Otol. Rhinol. Laryngol. Suppl. 175:1-16 (1998)] by estimating the three-dimensional (3D) cochlear lengths, electrode array intracochlear insertion depths, and characteristic frequency ranges for 13 more Nucleus-22 implant recipients based on in vivo computed tomography (CT) scans. Array insertion depths were correlated with NU-6 word scores (obtained one year after SPEAK strategy use) by these patients and the 13 who used the SPEAK strategy from the Ketten et al. study. For these 26 patients, the range of cochlear lengths was 29.1-37.4 mm. Array insertion depth range was 11.9-25.9 mm, and array insertion depth estimated from the surgeon's report was 1.14 mm longer than CT-based estimates. Given the assumption that the human hearing range is fixed (20-20,000 Hz) regardless of cochlear length, characteristic frequencies at the most apical electrode (estimated with Greenwood's equation [Greenwood DD (1990) A cochlear frequency--position function of several species--29 years later. J Acoust. Soc. Am. 33: 1344-1356] and a patient-specific constant as) ranged from 308 to 3674 Hz. Patients' NU-6 word scores were significantly correlated with insertion depth as a percentage of total cochlear length (R = 0.452; r2 = 0.204; p = 0.020), suggesting that part of the variability in word recognition across implant recipients can be accounted for by the position of the electrode array in the cochlea. However, NU-6 scores ranged from 4% to 81% correct for patients with array insertion depths between 47% and 68% of total cochlear length. Lower scores appeared related to low spiral ganglion cell survival (e.g., lues), aberrant current paths that produced facial nerve stimulation by apical electrodes (i.e., otosclerosis), central auditory processing difficulty, below-average verbal abilities, and early Alzheimer's disease. Higher scores appeared related to patients' high-average to above-average verbal abilities. Because most patients' scores increased with SPEAK use, it is hypothesized that they accommodated to the shift in frequency of incoming sound to a higher pitch percept with the implant than would normally be perceived acoustically.

Functional imaging of the auditory system: the use of positron emission tomography

Modern brain imaging methods now afford unprecedented opportunities for the in vivo study of central auditory system function. Positron emission tomography (PET) has been used as a functional imaging technique for more than 15 years to study the distribution of cerebral haemodynamic changes associated with auditory stimulation, in subjects with normal and abnormal auditory function. Many of these studies concern processes related to, but not identical with, audition, such as speech perception, melodic processing and directed attention. Additionally, PET has been used to explore auditory perception in clinical populations such as cochlear implantees, neurosurgical candidates and people with tinnitus and auditory hallucinations. The spatial resolution of PET does not appear sufficient to address questions of a fine anatomical grain, e.g. exploring functional specialization within the primary and secondary auditory cortex. Nevertheless, PET has considerable potential as a tool in basic research on, and clinical assessment of, many auditory phenomena. Although functional magnetic resonance imaging can now be used for many studies for which formerly only PET was suitable, PET still possesses unique advantages. For example, it permits acquisition of data from inferior frontal and anterior temporal areas, can be used with subjects with cochlear and other implants (such as pacemakers) and can be used to map neurochemical pathways and receptors.

Speech reception thresholds obtained in a symmetrical four-loudspeaker arrangement from bilateral users of MED-EL cochlear implants

OBJECTIVE

The purpose of the study was to investigate speech reception in noise in subjects who had undergone bilateral implantation with multichannel cochlear implants.

METHODS

Nine adults with bilateral MED-EL implants were included in the study. The subjects were tested using both implants and the better implant only. Tests were performed in a symmetrical setup, which ideally eliminates any head shadow effect. Speech tests included sentences in quiet and at various signal-to-noise ratios. From the results, the gain in signal-to-noise ratios at the speech reception threshold was determined.

RESULTS

All subjects showed a substantial gain in signal-to-noise ratios of approximately 4 dB on average. In addition, the gain in signal-to-noise ratios was essentially stable for as long as 4.4 years.

CONCLUSIONS

The results indicate that bilateral cochlear implant users are able to binaurally process speech.

Frequency mapping in cochlear implants

OBJECTIVE

To understand the short-term ("acute") effects of parametric variations to the frequency-to-electrode mapping on phoneme identification by Nucleus-22 cochlear implant listeners.

METHODS

Phoneme recognition was measured in five Nucleus-22 cochlear implant listeners using custom four-channel continuous interleaved sampler (CIS) processors. For the four-channel processors, speech signals were band-pass filtered into four broad frequency bands. The temporal envelope in each band was extracted by half-wave rectification and low-pass filtering at 160 Hz. The extracted envelope was then transformed to electric currents by a power function with an exponent of 0.2. The resulting electric currents were delivered to four electrode pairs (18,22), (13,17), (8,12), (3,7). The effect of frequency-to-electrode mapping was investigated by systematically varying the parameters of band-pass filters while fixing the electrode locations. Experiment 1 measured phoneme recognition as a function of the slope of band-pass filters. The slope of band-pass filters varied from 48 dB/octave to 6 dB/octave; the corner frequencies of band-pass filters were not varied. Experiment 2 measured phoneme recognition as a function of the distribution of band-pass filters across a fixed overall frequency range. The frequency divisions of a fixed overall frequency range were systematically varied from a logarithmic to a linear distribution. Experiment 3 measured phoneme recognition as a function of the bandwidth of the band-pass filters. The bandwidth of each filter varied from 0.2 to 2 octaves; the center frequencies for each band were not varied. No practice or feedback was provided for subjects in all experiments.

RESULTS

The slope of the band-pass filters had little effect on both vowel and consonant recognition. A slight performance drop was observed for only the shallowest slope condition (6 dB/octave). In contrast, the distribution of the band-pass filters had a strong effect on vowel recognition but a weak effect on consonant recognition. Best performance was achieved when a logarithmic or near-logarithmic frequency distribution was used to divide the overall frequency range. The bandwidth of the band-pass filters had a moderate effect on both vowel and consonant recognition. Vowel scores dropped significantly when the bandwidth of filters was too broad, whereas consonant scores dropped significantly when a narrower bandwidth was used.

CONCLUSION

Under "acute" testing conditions, phoneme recognition with a four-channel CIS strategy seems to be only mildly affected by the slope of the band-pass filters, but can be significantly affected by the distribution of filters as well as the bandwidth of the filters. Optimal or near-optimal performance can be achieved with a logarithmic frequency distribution. Vowels are more susceptible to broad bandwidths, whereas consonants are more susceptible to narrow bandwidths.

[Social integration of children with multichannel cochlear implant in the mainstream education system]

This paper is a preliminary report concerning result of social integration of children after cochlear implantation in the mainstream education system. It has been proofed that the presence of hearing impaired child in the class has an influence on other children. These other became more sensitive, less selfish and able to see needs of other human being. The tests were conducted on the group of 34 children and adolescents implanted in Poznań, learning in schools in the mainstream education system.

Rapid development of cortical auditory evoked potentials after early cochlear implantation

The aim of our research was to estimate the time course of development and plasticity of the human central auditory pathways following cochlear implantation. We recorded cortical auditory-evoked potentials in 3-year-old congenitally deaf children after they were fitted with cochlear implants. Immediately after implantation cortical response latencies resembled those of normal-hearing newborns. Over the next few months, the cortical evoked responses showed rapid changes in morphology and latency that resulted in age-appropriate latencies by 8 months after implantation. Overall, the development of cortical response latencies for the implanted children was more rapid than for their normal-hearing age-matched peers. Our results demonstrate a high degree of central auditory system plasticity during early human development.

The effect of channel interactions on speech recognition in cochlear implant subjects: predictions from an acoustic model

Acoustic models that produce speech signals with information content similar to that provided to cochlear implant users provide a mechanism by which to investigate the effect of various implant-specific processing or hardware parameters independent of other complicating factors. This study compares speech recognition of normal-hearing subjects listening through normal and impaired acoustic models of cochlear implant speech processors. The channel interactions that were simulated to impair the model were based on psychophysical data measured from cochlear implant subjects and include pitch reversals, indiscriminable electrodes, and forward masking effects. In general, spectral interactions degraded speech recognition more than temporal interactions. These effects were frequency dependent with spectral interactions that affect lower-frequency information causing the greatest decrease in speech recognition, and interactions that affect higher-frequency information having the least impact. The results of this study indicate that channel interactions, quantified psychophysically, affect speech recognition to different degrees. Investigation of the effects that channel interactions have on speech recognition may guide future research whose goal is compensating for psychophysically measured channel interactions in cochlear implant subjects.