Adult cochlear implant patient performance with evolving electrode technology

Preliminary Evidence to Support a De-Escalated Cochlear Implant Programming Paradigm for New Adult Recipients: A Systematic Review

Background: No standard schedule for cochlear implant (CI) programming has been developed, and common practices may have CI recipients seen in excess of what is necessary. The objective of this study was to review evidence for a de-escalated, evidence-based schedule for adult CI programming. Methods: Systematic review was undertaken in March 2023 of PubMed, Scopus, and CINAHL databases using the Preferred Reporting Items for Systemic Reviews and Meta-analyses (PRISMA) guidelines. Studies were included if (1) they evaluated an evidence-based programming/follow-up schedule in new adult CI patients or (2) they evaluated programming or outcomes in a longitudinal fashion such that they could inform CI follow-up strategies. Level of evidence was evaluated using the LEGEND evidence assessment tool. Results: Our review identified 940 studies. After screening with a priori inclusion criteria, 18 studies were ultimately included in this review. Of these, 2 demonstrated feasibility of de-escalated approaches to new adult CI programming. The remainder presented longitudinal speech and programming parameter data that demonstrated relative stability of both categories by 3 to 6 months post-activation. Conclusions: Overall, there is a paucity of literature evaluating any form of evidence-based CI programming or follow-up. Most applicable data derive from longitudinal outcomes featured in studies of other CI features, with only a handful of studies directly evaluating CI programming strategies over time. However, stability in outcomes and programming detailed in the available data supports consideration of a de-escalated programming paradigm that could primarily limit programming to the very early post-activation period (before 3 to 6 months) to enhance patient care and reduce operational strains on cochlear implant programs.

TMPRSS3 expression is limited in spiral ganglion neurons: implication for successful cochlear implantation

BACKGROUND

It is well established that biallelic mutations in transmembrane protease, serine 3 (TMPRSS3) cause hearing loss. Currently, there is controversy regarding the audiological outcomes after cochlear implantation (CI) for TMPRSS3-associated hearing loss. This controversy creates confusion among healthcare providers regarding the best treatment options for individuals with TMPRSS3-related hearing loss.

METHODS

A literature review was performed to identify all published cases of patients with TMPRSS3-associated hearing loss who received a CI. CI outcomes of this cohort were compared with published adult CI cohorts using postoperative consonant-nucleus-consonant (CNC) word performance. TMPRSS3 expression in mouse cochlea and human auditory nerves (HAN) was determined by using hybridisation chain reaction and single-cell RNA-sequencing analysis.

RESULTS

In aggregate, 27 patients (30 total CI ears) with TMPRSS3-associated hearing loss treated with CI, and 85% of patients reported favourable outcomes. Postoperative CNC word scores in patients with TMPRSS3-associated hearing loss were not significantly different than those seen in adult CI cohorts (8 studies). Robust Tmprss3 expression occurs throughout the mouse organ of Corti, the spindle and root cells of the lateral wall and faint staining within <5% of the HAN, representing type II spiral ganglion neurons. Adult HAN express negligible levels of TMPRSS3.

CONCLUSION

The clinical features after CI and physiological expression of TMPRSS3 suggest against a major role of TMPRSS3 in auditory neurons.

Longitudinal Speech Recognition Changes After Cochlear Implant: Systematic Review and Meta-analysis

OBJECTIVES

To examine patterns of change and plateau in speech recognition scores in postlingually hearing impaired adult cochlear implant recipients. The study also examines variations in change patterns for different speech materials and testing conditions.

STUDY DESIGN

Used systematic review with meta-analysis.

METHODS

Articles in English reporting speech recognition scores of adults with postlingual hearing loss at pre-implantation and at least two post-implantation time points were included. Statistically significant changes were determined by meta-analysis and the 95% confidence interval.

RESULTS

A total of 22 articles representing 1954 patients were included. Meta-analysis of mean difference demonstrated significant improvements in speech recognition score for words in quiet (37.4%; 95% confidence interval [34.7%, 40.7%]), sentences in quiet (49.4%; 95% confidence interval [44.9%, 53.9%]), and sentences in noise (30.8%; 95% confidence interval [25.2%, 36.4%]) from pre-op to 3 months. Scores continued to increase from 3 to 12 months but did not reach significance. Similarly, significant improvements from pre-op to 3 months were observed for consonant nucleus consonant (CNC) words in quiet (37.1%; 95% confidence interval [33.8%, 40.4%]), hearing in noise test (HINT) sentences in quiet (46.5%; 95% confidence interval [37.0%, 56.0%]), AzBio sentences in quiet (45.9%; 95% confidence interval [44.2%, 47.5%]), and AzBio sentences in noise (26.4%; 95% confidence interval [18.6%, 34.2%]). HINT sentences in noise demonstrated improvement from pre-op to 3 months (35.1%; 95% confidence interval [30.0%, 40.3%]) and from 3 to 12 months (15.5%; 95% confidence interval [7.2%, 23.8%]).

CONCLUSIONS

Mean speech recognition scores demonstrate significant improvement within the first 3 months, with no further statistically significant improvement after 3 months. However, large individual variation should be expected and future research is needed to explain the sources of these individual differences. Laryngoscope, 2022.

Brain Morphological Modifications in Congenital and Acquired Auditory Deprivation: A Systematic Review and Coordinate-Based Meta-Analysis

Neuroplasticity following deafness has been widely demonstrated in both humans and animals, but the anatomical substrate of these changes is not yet clear in human brain. However, it is of high importance since hearing loss is a growing problem due to aging population. Moreover, knowing these brain changes could help to understand some disappointing results with cochlear implant, and therefore could improve hearing rehabilitation. A systematic review and a coordinate-based meta-analysis were realized about the morphological brain changes highlighted by MRI in severe to profound hearing loss, congenital and acquired before or after language onset. 25 papers were included in our review, concerning more than 400 deaf subjects, most of them presenting prelingual deafness. The most consistent finding is a volumetric decrease in gray matter around bilateral auditory cortex. This change was confirmed by the coordinate-based meta-analysis which shows three converging clusters in this region. The visual areas of deaf children is also significantly impacted, with a decrease of the volume of both gray and white matters. Finally, deafness is responsible of a gray matter increase within the cerebellum, especially at the right side. These results are largely discussed and compared with those from deaf animal models and blind humans, which demonstrate for example a much more consistent gray matter decrease along their respective primary sensory pathway. In human deafness, a lot of other factors than deafness could interact on the brain plasticity. One of the most important is the use of sign language and its age of acquisition, which induce among others changes within the hand motor region and the visual cortex. But other confounding factors exist which have been too little considered in the current literature, such as the etiology of the hearing impairment, the speech-reading ability, the hearing aid use, the frequent associated vestibular dysfunction or neurocognitive impairment. Another important weakness highlighted by this review concern the lack of papers about postlingual deafness, whereas it represents most of the deaf population. Further studies are needed to better understand these issues, and finally try to improve deafness rehabilitation.

Current demographic and auditory profiles of adult cochlear implant candidates and factors affecting uptake

OBJECTIVES

Despite growth of CI and widening of implantation criteria, penetration rates remain low and the clinical profile of adult CI candidates has not substantially changed. This study evaluated the demographic and auditory profiles of current adult CI candidates and identified factors affecting CI uptake.

DESIGN

Preoperative data from patients who underwent CI candidacy evaluation between 2016-2018 were retrospectively reviewed. Data included demographics, medical reports, audiological results, and reasons for not pursuing implantation. Comparisons between candidates who pursued implantation and those who did not were performed.

STUDY SAMPLE

Ninety-five candidates (54 females), average age 52 years.

RESULTS

Most candidates exhibited post-lingual bilateral hearing loss with mean unaided PTA4 of 105dBHL and monosyllabic word score of 26%. Forty-nine candidates were implanted, and the main reason for not pursuing CI was candidates' reluctance. Candidates that pursued CI were mostly younger females with poorer unaided PTA4. Age was the only significant predictor of CI uptake.

CONCLUSIONS

While current candidates demonstrated greater demographic diversity and better speech perception compared to previous findings, unaided thresholds are still within the profound range. Our findings indicate that eligible candidates face barriers to the utilisation of CI, some of which are modifiable by means of updated candidacy protocols.

[Neurophysiological parameters for speech recognition in patients with cochlear implants]

OBJECTIVES

 Cochlea Implants (CI) are the preferred treatment for deaf and highly hearing imparied people. While deaf people already profit enormously from any regained hearing perception, it is not as easy to predict a profitable outcome for people with a remaining sense of hearing. To provide patients the best possible outcome in speech understanding, a lot of parameters have to be identified and adjusted. The aim of this study is to show the influence of objective parameters on classified speech understanding using collected data.

MATERIAL AND METHODS

 A total of 52 patients and 65 ears aged between 18 and 80 years were included in this study. ECAP-thresholds from intraoperative measurements and impedance were used as objective parameters. T- and C/M-levels were defined as subjective parameters. To classify the performance the value of speech understanding was used.

RESULTS

 Differences between both groups (age, time after implantation) were not significant. The gained word scores at 500 Hz correlated significantly with the results of the speech perception threshold on two-digit numbers. The electrode impedances correlated on average with speech understanding with constant variability. The distributions of objective and subjective parameters showed partially significant differences. Many distributions showed significant differences to the normal distribution. Accordingly, the overlapping areas of the significance levels are very narrow.

CONCLUSION

 Higher impedances and incorrectly adjusted T-levels resulted in a worse speech understanding. Relation of C/M-levels to ECAP thresholds seem to be crucial for good speech understanding.

Longitudinal outcomes of cochlear implantation and bimodal hearing in a large group of adults: A multicenter clinical study

OBJECTIVE

To evaluate speech understanding outcomes in a large adult cohort who demonstrated poor hearing performance with well fit hearing aids in the unilateral and bilateral or bimodal listening conditions at preimplant, 3-, 6- and 12-months.

SUBJECTS

Post-linguistically deafened adults (N = 100) with bilateral moderate-to-profound sensorineural hearing loss and limited functional benefit from well fit bilateral hearing aids.

METHOD

A multicenter, prospective, repeated-measures, within-subject controlled study was conducted. All subjects were implanted with a Slim Modiolar cochlear implant and were required to use bimodal stimulation (cochlear implant and hearing aid in contralateral ear) for 6-months postimplant and optionally to 12-months. Evaluations included: speech recognition for monosyllabic consonant-nucleus-consonant (CNC) words in quiet; AzBio sentences in coincident noise (at +5 and +10 dB signal-to-noise ratio (SNR)), in implant ear and bimodal conditions. All speech tests were performed at preimplant and 6-months postimplant for primary endpoint outcomes, and a subset of speech tests at 3- and 12-months.

RESULTS

In the implant ear only, at 3-, 6- and 12-months postimplant, 84%, 93% and 97% of subjects respectively, demonstrated significantly improved monosyllabic word scores in quiet compared to preimplant hearing aid scores (p < 0.05). At 12-months, a mean gain of 51% points, for monosyllabic words and 32% points for sentences in noise was observed (p < 0.001). In the bimodal condition, at 6-months postimplant, 87% of subjects demonstrated significantly improved monosyllabic word scores in quiet compared to preimplant bilateral hearing aid scores (p < 0.05). At 6-months, a mean gain of 40% points, for monosyllabic words was observed (p < 0.001). Speech scores for sentences in noise significantly improved for the bimodal condition at 6- and 12-months (p < 0.001). In addition to speech scores for the implanted ear, bimodal condition scores demonstrated further increments, especially for sentences in noise at 6- and 12-months (p < 0.001).

CONCLUSION

Results support that bimodal hearing is superior to bilateral hearing aids in this cohort of bilateral moderate-to-profound adult hearing aid users. Our study cohort demonstrated significant improvements for speech scores for the cochlear implant (CI) ear only and bimodal conditions compared to the baseline preimplant unilateral and bilateral hearing aid conditions respectively. The greatest gain in performance was in the first three months of device use with incremental improvement through 12 months. These findings indicate that when hearing aids fit to National Acoustics Laboratory (NAL-1) targets do not provide the necessary audibility needed for speech recognition, referral for CI-candidacy evaluation is strongly recommended.

TRIAL REGISTRATION

Clintrial.govNCT03007472. Registered 01/02/2017, https://clinicaltrials.gov/ct2/show/NCT03007472?term=clinical+evaluation+of+the+nucleus+CI532&draw=2&rank=2.

Current Profile of Adults Presenting for Preoperative Cochlear Implant Evaluation

Considerable advancements in cochlear implant technology (e.g., electric acoustic stimulation) and assessment materials have yielded expanded criteria. Despite this, it is unclear whether individuals with better audiometric thresholds and speech understanding are being referred for cochlear implant workup and pursuing cochlear implantation. The purpose of this study was to characterize the mean auditory and demographic profile of adults presenting for preoperative cochlear implant workup. Data were collected prospectively for all adult preoperative workups at Vanderbilt from 2013 to 2015. Subjects included 287 adults (253 postlingually deafened) with a mean age of 62.3 years. Each individual was assessed using the minimum speech test battery, spectral modulation detection, subjective questionnaires, and cognitive screening. Mean consonant-nucleus-consonant word scores, AzBio sentence scores, and pure-tone averages for postlingually deafened adults were 10%, 13%, and 89 dB HL, respectively, for the ear to be implanted. Seventy-three individuals (25.4%) met labeled indications for Hybrid-L and 207 individuals (72.1%) had aidable hearing in the better hearing ear to be used in a bimodal hearing configuration. These results suggest that mean speech understanding evaluated at cochlear implant workup remains very low despite recent advancements. Greater awareness and insurance accessibility may be needed to make cochlear implant technology available to those who qualify for electric acoustic stimulation devices as well as individuals meeting conventional cochlear implant criteria.

Factors Affecting Outcomes in Cochlear Implant Recipients Implanted With a Perimodiolar Electrode Array Located in Scala Tympani

OBJECTIVE

To identify primary biographic and audiologic factors contributing to cochlear implant (CI) performance variability in quiet and noise by controlling electrode array type and electrode position within the cochlea.

BACKGROUND

Although CI outcomes have improved over time, considerable outcome variability still exists. Biographic, audiologic, and device-related factors have been shown to influence performance. Examining CI recipients with consistent array type and electrode position may allow focused investigation into outcome variability resulting from biographic and audiologic factors.

METHODS

Thirty-nine adults (40 ears) implanted for at least 6 months with a perimodiolar electrode array known (via computed tomography [CT] imaging) to be in scala tympani participated. Test materials, administered CI only, included monosyllabic words, sentences in quiet and noise, and spectral ripple discrimination.

RESULTS

In quiet, scores were high with mean word and sentence scores of 76 and 87%, respectively; however, sentence scores decreased by an average of 35 percentage points when noise was added. A principal components (PC) analysis of biographic and audiologic factors found three distinct factors, PC1 Age, PC2 Duration, and PC3 Pre-op Hearing. PC1 Age was the only factor that correlated, albeit modestly, with speech recognition in quiet and noise. Spectral ripple discrimination strongly correlated with speech measures.

CONCLUSION

For these recipients with consistent electrode position, PC1 Age was related to speech recognition performance. Consistent electrode position may have contributed to high speech understanding in quiet. Inter-subject variability in noise may have been influenced by auditory/cognitive processing, known to decline with age, and mechanisms that underlie spectral resolution ability.

The “pull-back” technique for Nucleus 24 perimodiolar electrode insertion

OBJECTIVE: To observe the influence of electrode pull-back after cochlear implant insertion of Nucleus 24 perimodiolar electrodes.

STUDY DESIGN: In a prospective intraoperative study, we analyzed the impedances, neural response telemetry responses, and the spread of excitation after cochlear implant electrode insertion and compared these data to those obtained after a subsequent, controlled pull-back of the electrode. Postoperative depth of electrode insertion was controlled by x-ray.

SETTING: Tertiary referral center.

SUBJECTS: Six patients (4 male, 2 female; 18 to 69 years) were implanted with a Nucleus 24 (RCA) cochlear implant with a perimodiolar electrode.

RESULTS: After a controlled pull-back, a significant decrease of the spread of excitation at the stimuli electrodes 5, 10, 15, and a nonsignificant decrease at stimuli electrode 20 compared to the recordings after the primary normal insertion procedure was found. The mean electric compound action potential amplitude was increased with an apical-to-basal tendency. Impedances remained unchanged by the pull-back. Mean insertion depth at the postoperative x-ray control was 372 degrees (± 10.2).

CONCLUSION: Controlled cochlear implant electrode pull-back is a novel technique that optimizes objective intraoperative electrophysiological recordings in patients implanted with a Nucleus 24 perimodiolar cochlear implant by a greater approximation of the electrode to the modiolus. (Otolaryngol Head Neck Surg 2005;132:751-4.)

Evidence for the expansion of adult cochlear implant candidacy

OBJECTIVES

The primary objective of this study was to determine whether a revision and/or expansion of current audiologic cochlear implant candidacy criteria is warranted.

DESIGN

The study design was a retrospective review of postoperative speech perception performance for 22 adult cochlear implant recipients who demonstrated preoperative Consonant Nucleus Consonant word recognition scores of 30% or higher in the best-aided condition. This criterion was chosen to exceed that specified by the North American clinical trial of the Nucleus Freedom cochlear implant system.

RESULTS

The mean preoperative best-aided monosyllabic word score for the 22 patients was 41% correct. The degree of postoperative benefit for the best postoperative condition (electric only or bimodal) ranged from 10 to 68 percentage points with a mean benefit of 27 percentage points for the electric-only condition and 40 percentage points for the bimodal condition. Statistical analyses revealed highly significant differences between preoperative-aided, implant-only, and bimodal performance on Consonant Nucleus Consonant monosyllabic word recognition performance. That is, both postoperative scores--electric only and bimodal--were significantly different from one another and from the preoperative best-aided performance.

CONCLUSIONS

The current results suggest that a large-scale reassessment of manufacturer and Medicare preoperative audiologic candidacy criteria for adults is warranted to allow more hearing-impaired individuals to take advantage of the benefits offered by cochlear implantation.

Effects of hearing preservation on psychophysical responses to cochlear implant stimulation

Previous studies have shown that residual acoustic hearing supplements cochlear implant function to improve speech recognition in noise as well as perception of music. The current study had two primary objectives. First, we sought to determine how cochlear implantation and electrical stimulation over a time period of 14 to 21 months influence cochlear structures such as hair cells and spiral ganglion neurons. Second, we sought to investigate whether the structures that provide acoustic hearing also affect the perception of electrical stimulation. We compared psychophysical responses to cochlear implant stimulation in two groups of adult guinea pigs. Group I (11 animals) received a cochlear implant in a previously untreated ear, while group II (ten animals) received a cochlear implant in an ear that had been previously infused with neomycin to destroy hearing. Psychophysical thresholds were measured in response to pulse-train and sinusoidal stimuli. Histological analysis of all group I animals and a subset of group II animals was performed. Nine of the 11 group I animals showed survival of the organ of Corti and spiral ganglion neurons adjacent to the electrode array. All group I animals showed survival of these elements in regions apical to the electrode array. Group II animals that were examined histologically showed complete loss of the organ of Corti in regions adjacent and apical to the electrode array and severe spiral ganglion neuron loss, consistent with previous reports for neomycin-treated ears. Behaviorally, group II animals had significantly lower thresholds than group I animals in response to 100 Hz sinusoidal stimuli. However, group I animals had significantly lower thresholds than group II animals in response to pulse-train stimuli (0.02 ms/phase; 156 to 5,000 pps). Additionally, the two groups showed distinct threshold versus pulse rate functions. We hypothesize that the differences in detection thresholds between groups are caused by the electrical activation of the hair cells in group I animals and/or differences between groups in the condition of the spiral ganglion neurons.

Principles of design and biological approaches for improving the selectivity of cochlear implant electrodes

The perceptual performance of cochlear implant recipients seems to have reached a plateau in recent years. This may be attributable to inadequate neural selectivity of available intracochlear electrodes, caused by current spread and electrode interactions. Attempts to improve electrode selectivity have included manipulating the number and configuration of electrodes that are stimulated at any one time, displacing perilymph from the cochlea to restrict current flow along the cochlea, and reducing the distance between electrodes and neurons. One experimental approach by which the distance between neurons and electrodes may be reduced is to use neurotrophic factors to promote the regeneration of the peripheral dendrites of auditory neurons and guide them towards intracochlear electrodes. The likely requirements of a system for regenerating auditory neurons towards the cochlear electrode include either a stable release of neurotrophin, or transient neurotrophin followed by electrical stimulation; a close proximity of electrode to osseous spiral lamina or a polymer to bridge the gap between the two; guidance signals to attract neurons towards the electrode; patterning of the electrode surface to direct dendrites to electrode contacts and a 'stop' signal to arrest regeneration once the electrode has been reached.

Design and fabrication of multichannel cochlear implants for animal research

The effectiveness of multichannel cochlear implants depends on the activation of perceptually distinct regions of the auditory nerve. Increased information transfer is possible as the number of channels and dynamic range are increased and electrical and neural interaction among channels is reduced. Human and animal studies have demonstrated that specific design features of the intracochlear electrode directly affect these performance factors. These features include the geometry, size, and orientation of the stimulating sites, proximity of the device to spiral ganglion neurons, shape and position of the insulating carrier, and the stimulation mode (monopolar, bipolar, etc.). Animal studies to directly measure the effects of changes in electrode design are currently constrained by the lack of available electrodes that model contemporary clinical devices. This report presents methods to design and fabricate species-specific customizable electrode arrays. We have successfully implanted these arrays in guinea pigs and cats for periods of up to 14 months and have conducted acute electrophysiological experiments in these animals. Modifications enabling long-term intracochlear drug infusion are also described. Studies using these scale model arrays will improve our understanding of how these devices function in human subjects and how we can best optimize future cochlear implants.

Efficacy of a cochlear implant simultaneous analog stimulation strategy coupled with a monopolar electrode configuration

OBJECTIVES

The present study was performed to evaluate the efficacy and clinical feasibility of using monopolar stimulation with the Clarion Simultaneous Analog Stimulation (SAS) strategy in patients with cochlear implants.

METHODS

Speech recognition by 10 Clarion cochlear implant users was evaluated by means of 4 different speech processing strategy/electrode configuration combinations; ie, SAS and Continuous Interleaved Sampling (CIS) strategies were each used with monopolar (MP) and bipolar (BP) electrode configurations. The test measures included consonants, vowels, consonant-nucleus-consonant words, and Hearing in Noise Test sentences with a +10 dB signal-to-noise ratio. Additionally, subjective judgments of sound quality were obtained for each strategy/configuration combination.

RESULTS

All subjects but 1 demonstrated open-set speech recognition with the SAS/MP combination. The group mean Hearing in Noise Test sentence score for the SAS/MP combination was 31.6% (range, 0% to 92%) correct, as compared to 25.0%, 46.7%, and 37.8% correct for the CIS/BP, CIS/MP, and SAS/BP combinations, respectively. Intersubject variability was high, and there were no significant differences in mean speech recognition scores or mean preference ratings among the 4 strategy/configuration combinations tested. Individually, the best speech recognition performance was with the subject's everyday strategy/configuration combination in 72% of the applicable cases. If the everyday strategy was excluded from the analysis, the subjects performed best with the SAS/MP combination in 37.5% of the remaining cases.

CONCLUSIONS

The SAS processing strategy with an MP electrode configuration gave reasonable speech recognition in most subjects, even though subjects had minimal previous experience with this strategy/configuration combination. The SAS/MP combination might be particularly appropriate for patients for whom a full dynamic range of electrical hearing could not be achieved with a BP configuration.

Effects of electrode design and configuration on channel interactions

A potential shortcoming of existing multichannel cochlear implants is electrical-field summation during simultaneous electrode stimulation. Electrical-field interactions can disrupt the stimulus waveform prior to neural activation. To test whether speech intelligibility can be degraded by electrical-field interaction, speech recognition performance and interaction were examined for three Clarion electrode arrays: the pre-curved, enhanced bipolar electrode array, the enhanced bipolar electrode with an electrode positioner, and the Hi-Focus electrode with a positioner. Channel interaction was measured by comparing stimulus detection thresholds for a probe signal in the presence of a sub-threshold perturbation signal as a function of the separation between the two simultaneously stimulated electrodes. Correct identification of vowels, consonants, and words in sentences was measured with two speech strategies: one which used simultaneous stimulation and another which used sequential stimulation. Speech recognition scores were correlated with measured electrical-field interaction for the strategy which used simultaneous stimulation but not the strategy which used sequential stimulation. Higher speech recognition scores with the simultaneous strategy were generally associated with lower levels of electrical-field interaction. Electrical-field interaction accounted for as much as 70% of the variance in speech recognition scores, suggesting that electrical-field interaction is a significant contributor to the variability found across patients who use simultaneous strategies.

Pediatric Cochlear Implant Patient Performance as a Function of Age at Implantation

OBJECTIVE

The objective of this study was to examine the effect that age at implantation has on performance of children who received multichannel cochlear implants.

STUDY DESIGN

This is a retrospective study of 295 children who were broken down into 5 age groups based on age at implantation: 1-3 years, 3-5 years, 5-7 years, 7-9 years, and 9-11 years. Speech perception test scores obtained 12, 24, and 36 months postactivation were compared for the 5 groups using repeated-measures analysis of variance.

SETTING

This study was carried out at a tertiary academic medical center.

PATIENTS

Subjects consisted of 295 children who ranged in age from 12 months to 10 years 11 months at the time they obtained their cochlear implant.

INTERVENTION

All patients received their cochlear implant at a single implant facility.

MAIN OUTCOME MEASURES

Performance on several speech perception tests was compared 12, 24, and 36 months postactivation. Performance was evaluated as a function of age at implantation.

RESULTS

Patients in all 5 groups demonstrated improved scores when compared with scores obtained preoperatively with hearing aids. Repeated-measures analysis of variance (ANOVA) revealed a significant group by time interaction for 3 of the 5 measures. For all three of these measures, children implanted at younger ages demonstrated greater gains in speech perception over time than children implanted at older ages.

CONCLUSIONS

These results are in agreement with those of previous studies indicating that early implantation facilitates improved development of speech perception skills in profoundly deaf children.

Cochlear implants: some likely next steps

The history of cochlear implants is marked by large improvements in performance, especially over the past two decades and especially due to the development of ever-better processing strategies. Although the progress to date has been substantial, present devices still do not restore normal speech reception, even for top performers and particularly for listening to speech in competition with noise or other talkers. In addition, a wide range of outcomes persists, with some patients receiving little benefit using the same devices that support high levels of speech reception for others. The purpose of this review is to describe some likely possibilities for further improvement, including (a) combined electric and acoustic stimulation of the auditory system for patients with significant residual hearing, (b) use of bilateral implants, (c) a closer replication with implants of the processing steps in the normal cochlea, and (d) applications of knowledge about factors that are correlated with outcomes to help patients presently at the low end of the performance scale.

HiResolutionTM and Conventional Sound Processing in the HiResolutionTM Bionic Ear: Using Appropriate Outcome Measures to Assess Speech Recognition Ability

OBJECTIVE

This study compared speech perception benefits in adults implanted with the HiResolution (HiRes) Bionic Ear who used both conventional and HiRes sound processing. A battery of speech tests was used to determine which formats were most appropriate for documenting the wide range of benefit experienced by cochlear-implant users.

STUDY DESIGN

A repeated-measures design was used to assess postimplantation speech perception in adults who received the HiResolution Bionic Ear in a recent clinical trial. Patients were fit first with conventional strategies and assessed after 3 months of use. Patients were then switched to HiRes sound processing and assessed again after 3 months of use. To assess the immediate effect of HiRes sound processing on speech perception performance, consonant recognition testing was performed in a subset of patients after 3 days of HiRes use and compared with their 3-month performance with conventional processing.

SETTING

Subjects were implanted and evaluated at 19 cochlear implant programs in the USA and Canada affiliated primarily with tertiary medical centers.

PATIENTS

Patients were 51 postlinguistically deafened adults.

MAIN OUTCOME MEASURES

Speech perception was assessed using CNC monosyllabic words, CID sentences and HINT sentences in quiet and noise. Consonant recognition testing was also administered to a subset of patients (n = 30) using the Iowa Consonant Test presented in quiet and noise. All patients completed a strategy preference questionnaire after 6 months of device use.

RESULTS

Consonant identification in quiet and noise improved significantly after only 3 days of HiRes use. The mean improvement from conventional to HiRes processing was significant on all speech perception tests. The largest differences occurred for the HINT sentences in noise. Ninety-six percent of the patients preferred HiRes to conventional sound processing. Ceiling effects occurred for both sentence tests in quiet.

CONCLUSIONS

Although most patients improved after switching to HiRes sound processing, the greatest differences were seen in the 'poor' performers because 'good' performers often reached ceiling performance, especially on tests in quiet. Future evaluations of cochlear-implant benefit should make use of more difficult measures, especially for 'good' users. Nonetheless, a range of difficulty must remain in test materials to document benefit in the entire population of implant recipients.

Coding of sounds in the auditory system and its relevance to signal processing and coding in cochlear implants

OBJECTIVE

To review how the properties of sounds are "coded" in the normal auditory system and to discuss the extent to which cochlear implants can and do represent these codes.

DATA SOURCES

Data are taken from published studies of the response of the cochlea and auditory nerve to simple and complex stimuli, in both the normal and the electrically stimulated ear. REVIEW CONTENT: The review describes: 1) the coding in the normal auditory system of overall level (which partly determines perceived loudness), spectral shape (which partly determines perceived timbre and the identity of speech sounds), periodicity (which partly determines pitch), and sound location; 2) the role of the active mechanism in the cochlea, and particularly the fast-acting compression associated with that mechanism; 3) the neural response patterns evoked by cochlear implants; and 4) how the response patterns evoked by implants differ from those observed in the normal auditory system in response to sound. A series of specific issues is then discussed, including: 1) how to compensate for the loss of cochlear compression; 2) the effective number of independent channels in a normal ear and in cochlear implantees; 3) the importance of independence of responses across neurons; 4) the stochastic nature of normal neural responses; 5) the possible role of across-channel coincidence detection; and 6) potential benefits of binaural implantation.

CONCLUSIONS

Current cochlear implants do not adequately reproduce several aspects of the neural coding of sound in the normal auditory system. Improved electrode arrays and coding systems may lead to improved coding and, it is hoped, to better performance.