Cochlear Implant Fitting Research Articles

Setting and reaching targets with computer-assisted cochlear implant fitting.

Objective. The paper aims to demonstrate the feasibility of defining a substantial set of psychoacoustic outcome measures with preset targets and to adopt a systematic methodology for reaching these targets in a large group of subjects, by more than one clinical centre. Design. Retrospective data analysis. Setting. Multicentre with 14 participating centres. Patients. 255 adults and children using the Advanced Bionics HiRes90k cochlear implant. Intervention. Target driven fitting with the fitting to outcomes expert (FOX) system. Main Outcome Measures. For each patient, 66 measurable psychoacoustical outcomes were recorded several times after cochlear implantation: free field audiometry (6 measures) and speech audiometry (4), spectral discrimination (20), and loudness growth (36), defined from the A§E test battery. These outcomes were reduced to 22 summary variables. The initial results were compared with the latest results. Results. The state of the fitting process could be well monitored by means of the measured variables. The use of the FOX computer assisted CI-programming significantly improved the proportion of the 22 variables on target. When recipients used the automated MAPs provided at switch-on, more than half (57%) of the 22 targets were already achieved before any further optimisation took place. Once the FOX system was applied there was a significant 24% (P < 0.001) increase in the number of targets achieved. Conclusions. This study demonstrates that it is feasible to set targets and to report on the effectiveness of a fitting strategy in terms of these targets. FOX provides an effective tool for achieving a systematic approach to programming, allowing for better optimisation of recipients' MAPs. The setting of well-defined outcome targets allowed a range of different centres to successfully apply a systematic methodology to monitoring the quality of the programming provided.

The effect of language structure on linguistic strengths and weaknesses in children with cochlear implants: Evidence from Italian

ABSTRACTPrevious studies have found that the early fitting of cochlear implants in children has beneficial effects on their expressive and receptive language. However, different ages are identified in different studies, and some studies present contradictory results. Starting from these observations, our study suggests that at least two additional factors play an important role in determining linguistic outcomes. The first is the area of language under investigation: lexicon, phonology, morphosyntax, semantics, and pragmatics. The second factor is the typological features of the child's target language. Our study, which involved 33 Italian-speaking children who received a cochlear implant and 33 age and gender matched controls, reveals that lexical, semantic, pragmatic, and phonological knowledge are not particularly vulnerable in these children. By contrast, one area of morphosyntax (production of clitic pronouns) is especially challenging. In addition, an effect of age of implantation was found only in this morphosyntactic area. This is the first study on language development in Italian-speaking children with cochlear implants.

Dynamic-range compression affects the lateral position of sounds

Dynamic-range compression acting independently at each ear in a bilateral hearing-aid or cochlear-implant fitting can alter interaural level differences (ILDs) potentially affecting spatial perception. The influence of compression on the lateral position of sounds was studied in normal-hearing listeners using virtual acoustic stimuli. In a lateralization task, listeners indicated the leftmost and rightmost extents of the auditory event and reported whether they heard (1) a single, stationary image, (2) a moving/gradually broadening image, or (3) a split image. Fast-acting compression significantly affected the perceived position of high-pass sounds. For sounds with abrupt onsets and offsets, compression shifted the entire image to a more central position. For sounds containing gradual onsets and offsets, including speech, compression increased the occurrence of moving and split images by up to 57 percentage points and increased the perceived lateral extent of the auditory event. The severity of the effects was reduced when undisturbed low-frequency binaural cues were made available. At high frequencies, listeners gave increased weight to ILDs relative to interaural time differences carried in the envelope when compression caused ILDs to change dynamically at low rates, although individual differences were apparent. Specific conditions are identified in which compression is likely to affect spatial perception.

F011 The intelligent agent FOX to assist the fitting of cochlear implants in children

To report an integrating surgical method of Vibrant SoundBridge (VSB) implant and auricle reconstruction.4 cases of congenital bilateral external/middle ear malformation were enrolled. All of them were diagnosed as bilateral bony atresia and grade III microtia. Stapes vibroplasty was performed for all subjects in one operation with auricle reconstruction stage 3. The clinical information and hearing outcomes were analyzed.Satisfied aesthetic outcomes were confirmed by sculptured outline and symmetric shape on both sides. Mean improvement in hearing threshold with VSB activation was 25.9 dB HL, while mean scores of speech recognition test were 21.8–46.3%.Combined surgical method of VSB implant and aesthetic reconstruction is safe and efficient for congenital external/middle ear malformation case.

Neural Response Telemetry Reconsidered: I. The Relevance of ECAP Threshold Profiles and Scaled Profiles to Cochlear Implant Fitting

For more than a decade, Neural Response Telemetry (NRT) has provided direct access to the electrically evoked compound action potential (ECAP) as elicited by the Nucleus cochlear implant. When used clinically during fitting, ECAP threshold profiles are applied by shifting the profile to the audible threshold and comfort level boundaries (the T- and C-level profiles, respectively). The resulting profiles, to date, have matched the curvature of the ECAP threshold profile exactly. When compared with psychophysical profiles, previous studies have shown that this approach incurs errors in program levels that are no better than flat or population mean profiles. However, C-level profiles are observed to be flatter than T-level profiles. Accordingly, ECAP threshold profiles are flattened in this study when applied at increasing stimulus levels, and the effectiveness of this approach is evaluated among other methods. In phase I, ECAP thresholds (via AutoNRT) and T- and C-levels were measured from 15 adult Nucleus Freedom implantees. Psychophysical levels were measured using pulse train stimuli at six different stimulation rates, spanning 80 to 3500 Hz. The different rates spread T- and C-levels across a range of stimulus levels. At each of these levels, a scaling factor of best fit was calculated such that the shifted ECAP threshold profile, when scaled (0 giving a flat profile, 1 giving an unmodified profile), gave the best fit to the corresponding psychophysical profile. From the 148 such T- and C-level profiles, a single profile scaling model was determined by a simple linear regression. In phase II, the model was tested on data using three separate stimulation rates (250, 900, and 2400 Hz) and 14 additional subjects. The root mean square psychophysical level mismatch of the ECAP threshold profile, the scaled ECAP threshold profile, a flat profile, and a mean population profile was calculated per subject and per stimulation rate, and the differences in the means of these calculations were compared. In phase III, 13 separate subjects evaluated the scaled ECAP-based program during a 2 wk trial, comparing the new program to a flat program and a conventional ECAP-based program with unmodified ECAP threshold profiles. A questionnaire captured their subjective preferences. In phase I, the profile scaling model constructed from the data prescribed a flattening of the ECAP threshold profile with increasing mean T- or C-level (in CL units): scale = 1.38 - 0.0043 PsychoMean. In phase II, the scaled ECAP-based profiles were found to fit the psychophysical profiles significantly better in all test configurations (typically of the order of 5% dynamic range) compared with all other profiles. In phase III, 62% of subjects preferred the scaled ECAP-based program, whereas 8% preferred the conventional ECAP-based program, 15% the flat program and 15% had no preference. Analyses of the questionnaires revealed significantly higher ratings for the scaled ECAP-based programs, whereas the conventional ECAP-based programs were not rated differently than the flat programs. The scaled ECAP threshold profile method provides a clinically significant enhancement to ECAP-based fitting methods, confirming the value of the ECAP threshold profile to cochlear implant fitting.

Better fitting of cochlear implants: modeling loudness for acoustic and electric stimuli

It is becoming more common for cochlear implant (CI) recipients to have some useful acoustic hearing post-operatively. Such CI users may benefit from simultaneous use of an acoustic hearing aid (HA). To provide a satisfactory fitting of both types of devices, it is helpful to make the loudness perceived via each device as similar as possible. In practice, this is usually attempted by adjusting the sensitivity and/or gain of each device during fitting, but it is often not clear whether or how well the loudness of the devices has been matched for each user. In this study, established numerical models of loudness for both acoustic and electric stimulation were used to investigate this problem. The models' outputs were compared to published psychophysical data and were found to approximate the main patterns observed in those data. They also showed that, theoretically, there would be differences in the loudness perceived with each type of device when sounds with varying frequency content and level were heard. Future sound processors and/or fitting techniques developed specifically for CI recipients with usable acoustic hearing could apply such computational models of loudness to improve simultaneous use of the two types of device.

Quality of Life for Children With Cochlear Implants: Perceived Benefits and Problems and the Perception of Single Words and Emotional Sounds

This study examined children's self-reported quality of life with a cochlear implant as related to children's actual perceptions of speech and the emotional information conveyed by sound. Effects of age at amplification with hearing aids and fitting of cochlear implants on perceived quality of life were also investigated. A self-reported quality of life questionnaire and assessments of speech perception (single words) and emotion identification were administered to a sample of 37 children with cochlear implants who were congenitally deaf, who were 5-14 years of age, and who all used spoken language. The children reported significant improvement in quality of life because of their cochlear implants, and they also reported low levels of concern about typical problems associated with wearing an implant. The children's perceived quality of life did not significantly predict speech perception performance at the single word level. In contrast, increased quality of life predicted better performance on the emotion identification task. Age at first use of amplification predicted perceived quality of life. The findings regarding age reinforce the importance of early detection and intervention for children's positive quality of life with cochlear implants later in childhood.

Frequency-Specific Electrocochleography Indicates that Presynaptic and Postsynaptic Mechanisms of Auditory Neuropathy Exist

The physiological mechanisms underlying auditory neuropathy (AN) remain unclear and it is likely that the multiple disruptions are classified under the broadly defined term. Cochlear implantation is being more widely used in this population to bypass the suspected site-of-lesion although a number of cases have been identified within the Sydney Cochlear Implant Centre where this management strategy has been unsuccessful. It is likely that this relates to the different physiological mechanisms underlying AN. To investigate the site-of-lesion in AN, frequency-specific round window electrocochleography (ECochG) was used to assess local hair-cell, dendritic, and axonal currents generated within the cochlea in 14 subjects with AN and compared with responses from two normally hearing subjects. ECochG results were then compared with electrically evoked auditory brain stem response (EABR) measured after cochlear implantation. The results of this study demonstrate that two dominant patterns of ECochG waveforms (produced by a high-frequency alternating tone burst) can be identified in this population of AN subjects: (a) gross waveform showing a prolonged summating potential (SP) latency that, in most cases, is followed by a small compound action potential; and (b) gross waveform showing a normal latency SP waveform followed by a broad negative potential [assumed to reflect the dendritic potential (DP) identified in anaesthetized guinea-pigs]. This study demonstrates that in most subjects (n = 7) with a prolonged latency SP but no DP, normal morphology EABR waveforms were elicited for all electrode channels. On the other hand, all subjects (n = 7) who showed a normal latency SP followed by a broad negative DP, showed EABR waveforms that were absent or having poor wave V morphology. The authors' interpretation of this is that ECochG results may provide a classification of AN into pre- and postsynaptic lesions. We suggest that a presynaptic and postsynaptic type of AN exist that may have implications for the fitting of cochlear implants.

Algorithme évolutionnaire interactif. Application au réglage automatique d'implant cochléaire

This paper describes an interactive evolutionary algorithm dedicated to Cochlear Implants fitting. The algorithm automatically suggests different fittings that are evaluated by the patient along predefined criteria: comfort and speech undedrstanding. The evolutionary process is guided by the evaluation of the patient. The interaction with the patient is done through a PDA (Personal Data Assistant). The main advantage to use this lightweight terminal for the evaluation is to give the patient a full autonomy, and lift all constraints (hospital, environmental, temporal...) allowing him to optimise his CI fitting in any noise environment. This work exposes the first medical application of such an algorithm for Cochlear Implant fitting. Obtained results on a patient are presented and discussed.

Auditory speech sounds evaluation (A§E®): a new test to assess detection, discrimination and identification in hearing impairment

This paper describes a set of suprathreshold tests, available as a software package (A§E®), for the auditory evaluation of the hearing impaired. It uses isolated speech sounds as test material for a discrimination, identification and detection test, and is specifically suited to test preverbal children. All tests allow strict analytical interpretation. The test material and procedures are described. Their clinical use is illustrated. The authors claim that suprathreshold tests are feasible in the preverbal child, allowing analytical evaluation of the auditory capacities. These tests are complementary to the routinely used detection tests and add significantly to the hearing evaluation in preverbal children. The authors recommend the phoneme discrimination test for selection of cochlear implant candidates and for the evaluation and fitting of cochlear implants. Copyright © 2006 John Wiley & Sons, Ltd.

Parental Distress: The Initial Phase of Hearing Aid and Cochlear Implant Fitting

The results of previous cross-section studies suggest that childhood hearing impairment may lead to parental psychosocial stress. The present study investigated whether modifications in parental psychic state can be ascertained in connection with the child's treatment events and the child's hearing and speech status, in a prospective study design. Data were available on 116 fathers and mothers regarding the pre-cochlear implant examination or hearing aid fitting of their child. In the course of the child's treatment, parental quality of life improved from a low to a normal level. Among children who were at the stage of pre-examination for a cochlear implant, better hearing and speech capacity was linked to more severe impairment of the parental state. It is emphasized that the parents whose children showed comparatively good language development at the time of pre-examination for a cochlear implant were especially subjected to stress.

Monaural and binaural loudness measures in cochlear implant users with contralateral residual hearing.

The aim was to measure the loudness of monaural and binaural stimuli in a group of cochlear implant users who had residual hearing in the nonimplanted ear, and to consider the implications of these measures for a binaural fitting consisting of a hearing aid and an implant in opposite ears. Three independent hypotheses were addressed: that the shapes of the electric and acoustic loudness growth functions would be similar, although the dynamic ranges would differ; that standard implant and hearing aid fittings would result in substantial loudness mismatches between the acoustic and electric signals; and that loudness summation would occur for binaural combinations of electric and acoustic signals. A modified version of the "Loudness Growth in 1/2-Octave Bands" method (Allen, Hall, & Jeng, 1990) was used to measure loudness growth for each ear of nine subjects. At the time of the experiment, the subject group included all implant users in Melbourne and Denver who were available for research and who also had sufficient residual hearing to use a hearing aid in the nonimplanted ear. Five acoustic frequencies and five electrodes were measured for each subject. The same subjects also estimated the loudness of a set of stimuli including monaural and binaural signals chosen to cover the loudness range from very soft to loud. The shapes of the averaged loudness growth functions were similar in impaired and electrically stimulated ears, although the shapes of iso-loudness curves were quite different in the two ears, and dynamic ranges varied considerably. Calculations based on the psychophysical data demonstrated that standard fitting procedures for cochlear implants and hearing aids lead to a complex pattern of loudness differences between the ears. A substantial amount of loudness summation was observed for the binaural stimuli, with most summation occurring when the acoustic and electric components were of equal loudness. This is consistent with observations for subjects with normal hearing and subjects with bilaterally impaired hearing. These experiments provide data on which criteria and methods for the binaural fitting of cochlear implants and hearing aids may be based. It is unlikely that standard monaural fitting methods for cochlear implants and hearing aids will result in balanced loudness between the two ears across a reasonably broad range of frequencies and levels. It is also likely that output levels of both devices will need to be reduced relative to a monaural fitting to compensate for the binaural summation of loudness in some listeners.