Neuronal Development of Hearing and Language: Cochlear Implants and Critical Periods.

The modern cochlear implant (CI) is the most successful neural prosthesis developed to date. CIs provide hearing to the profoundly hearing impaired and allow the acquisition of spoken language in children born deaf. Results from studies enabled by the CI have provided new insights into (a) minimal representations at the periphery for speech reception, (b) brain mechanisms for decoding speech presented in quiet and in acoustically adverse conditions, (c) the developmental neuroscience of language and hearing, and (d) the mechanisms and time courses of intramodal and cross-modal plasticity. Additionally, the results have underscored the interconnectedness of brain functions and the importance of top-down processes in perception and learning. The findings are described in this review with emphasis on the developing brain and the acquisition of hearing and spoken language.

The Impact of Hearing Loss and Its Treatment on Health-Related Quality of Life Utility: a Systematic Review with Meta-analysis.

BACKGROUND: Hearing loss significantly impacts health-related quality of life (QoL), yet the effects of current treatments on QoL utility remain uncertain. Our objective was to describe the impact of untreated and treated hearing loss on QoL utility to inform hearing healthcare policy. METHODS: We searched databases for articles published through 02/01/2021. Two independent reviewers screened for articles that reported elicitation of general QoL utility values for untreated and treated hearing loss health states. We extracted data and quality indicators from 62 studies that met the inclusion criteria. RESULTS: Included studies predominately used observational pre/post designs (61%), evaluated unilateral cochlear implantation (65%), administered the Health Utilities Index 3 (HUI3; 71%), and were conducted in Europe and North America (84%). In general, treatment of hearing loss improved post-treatment QoL utility when measured by most methods except the Euro-QoL 5 dimension (EQ-5D). In meta-analysis, hearing aids for adult mild-to-moderate hearing loss compared to no treatment significantly improved HUI3-estimated QoL utility (3 studies; mean change=0.11; 95% confidence interval (CI): 0.07 to 0.14) but did not impact EQ-5D-estimated QoL (3 studies; mean change=0.0; 95% CI: -0.03 to 0.04). Cochlear implants improved adult QoL utility 1-year post-implantation when measured by the HUI3 (7 studies; mean change=0.17; 95% CI: 0.11 to 0.23); however, pediatric VAS-estimated QoL utility was non-significant (4 studies; mean change=0.12; 95% CI: -0.02 to 0.25). The quality of included studies was limited by failure to report missingness of data and low survey response rates. Our study was limited by heterogeneous study populations and designs. FINDINGS: Treatment of hearing loss significantly improves QoL utility, and the HUI3 and VAS were most sensitive to improvements in hearing. Improved access to hearing healthcare should be prioritized. SYSTEMATIC REVIEW REGISTRATION: PROSPERO: CRD42021253314.

Global hearing health care: new findings and perspectives.

In 2015, approximately half a billion people had disabling hearing loss, about 6·8% of the world's population. These numbers are substantially higher than estimates published before 2013, and point to the growing importance of hearing loss and global hearing health care. In this Review, we describe the burden of hearing loss and offer our and others' recommendations for halting and then reversing the continuing increases in this burden. Low-cost possibilities exist for prevention of hearing loss, as do unprecedented opportunities to reduce the generally high treatment costs. These possibilities and opportunities could and should be exploited. Additionally, a comprehensive worldwide initiative like VISION 2020 but for hearing could provide a focus for support and also enable and facilitate the increased efforts that are needed to reduce the burden. Success would produce major personal and societal gains, including gains that would help to fulfil the "healthy lives" and "disability inclusive" goals in the UN's new 2030 Agenda for Sustainable Development.

Effects of Electrical Stimulation in the Inferior Colliculus on Frequency Discrimination by Rhesus Monkeys and Implications for the Auditory Midbrain Implant.

UNLABELLED: Understanding the relationship between the auditory selectivity of neurons and their contribution to perception is critical to the design of effective auditory brain prosthetics. These prosthetics seek to mimic natural activity patterns to achieve desired perceptual outcomes. We measured the contribution of inferior colliculus (IC) sites to perception using combined recording and electrical stimulation. Monkeys performed a frequency-based discrimination task, reporting whether a probe sound was higher or lower in frequency than a reference sound. Stimulation pulses were paired with the probe sound on 50% of trials (0.5-80 µA, 100-300 Hz, n = 172 IC locations in 3 rhesus monkeys). Electrical stimulation tended to bias the animals' judgments in a fashion that was coarsely but significantly correlated with the best frequency of the stimulation site compared with the reference frequency used in the task. Although there was considerable variability in the effects of stimulation (including impairments in performance and shifts in performance away from the direction predicted based on the site's response properties), the results indicate that stimulation of the IC can evoke percepts correlated with the frequency-tuning properties of the IC. Consistent with the implications of recent human studies, the main avenue for improvement for the auditory midbrain implant suggested by our findings is to increase the number and spatial extent of electrodes, to increase the size of the region that can be electrically activated, and to provide a greater range of evoked percepts. SIGNIFICANCE STATEMENT: Patients with hearing loss stemming from causes that interrupt the auditory pathway after the cochlea need a brain prosthetic to restore hearing. Recently, prosthetic stimulation in the human inferior colliculus (IC) was evaluated in a clinical trial. Thus far, speech understanding was limited for the subjects and this limitation is thought to be partly due to challenges in harnessing the sound frequency representation in the IC. Here, we tested the effects of IC stimulation in monkeys trained to report the sound frequencies they heard. Our results indicate that the IC can be used to introduce a range of frequency percepts and suggest that placement of a greater number of electrode contacts may improve the effectiveness of such implants.

A Binaural Cochlear Implant Sound Coding Strategy Inspired by the Contralateral Medial Olivocochlear Reflex.

OBJECTIVES: In natural hearing, cochlear mechanical compression is dynamically adjusted via the efferent medial olivocochlear reflex (MOCR). These adjustments probably help understanding speech in noisy environments and are not available to the users of current cochlear implants (CIs). The aims of the present study are to: (1) present a binaural CI sound processing strategy inspired by the control of cochlear compression provided by the contralateral MOCR in natural hearing; and (2) assess the benefits of the new strategy for understanding speech presented in competition with steady noise with a speech-like spectrum in various spatial configurations of the speech and noise sources. DESIGN: Pairs of CI sound processors (one per ear) were constructed to mimic or not mimic the effects of the contralateral MOCR on compression. For the nonmimicking condition (standard strategy or STD), the two processors in a pair functioned similarly to standard clinical processors (i.e., with fixed back-end compression and independently of each other). When configured to mimic the effects of the MOCR (MOC strategy), the two processors communicated with each other and the amount of back-end compression in a given frequency channel of each processor in the pair decreased/increased dynamically (so that output levels dropped/increased) with increases/decreases in the output energy from the corresponding frequency channel in the contralateral processor. Speech reception thresholds in speech-shaped noise were measured for 3 bilateral CI users and 2 single-sided deaf unilateral CI users. Thresholds were compared for the STD and MOC strategies in unilateral and bilateral listening conditions and for three spatial configurations of the speech and noise sources in simulated free-field conditions: speech and noise sources colocated in front of the listener, speech on the left ear with noise in front of the listener, and speech on the left ear with noise on the right ear. In both bilateral and unilateral listening, the electrical stimulus delivered to the test ear(s) was always calculated as if the listeners were wearing bilateral processors. RESULTS: In both unilateral and bilateral listening conditions, mean speech reception thresholds were comparable with the two strategies for colocated speech and noise sources, but were at least 2 dB lower (better) with the MOC than with the STD strategy for spatially separated speech and noise sources. In unilateral listening conditions, mean thresholds improved with increasing the spatial separation between the speech and noise sources regardless of the strategy but the improvement was significantly greater with the MOC strategy. In bilateral listening conditions, thresholds improved significantly with increasing the speech-noise spatial separation only with the MOC strategy. CONCLUSIONS: The MOC strategy (1) significantly improved the intelligibility of speech presented in competition with a spatially separated noise source, both in unilateral and bilateral listening conditions; (2) produced significant spatial release from masking in bilateral listening conditions, something that did not occur with fixed compression; and (3) enhanced spatial release from masking in unilateral listening conditions. The MOC strategy as implemented here, or a modified version of it, may be usefully applied in CIs and in hearing aids.

Roles of the Contralateral Efferent Reflex in Hearing Demonstrated with Cochlear Implants.

Our two ears do not function as fixed and independent sound receptors; their functioning is coupled and dynamically adjusted via the contralateral medial olivocochlear efferent reflex (MOCR). The MOCR possibly facilitates speech recognition in noisy environments. Such a role, however, is yet to be demonstrated because selective deactivation of the reflex during natural acoustic listening has not been possible for human subjects up until now. Here, we propose that this and other roles of the MOCR may be elucidated using the unique stimulus controls provided by cochlear implants (CIs). Pairs of sound processors were constructed to mimic or not mimic the effects of the contralateral MOCR with CIs. For the non-mimicking condition (STD strategy), the two processors in a pair functioned independently of each other. When configured to mimic the effects of the MOCR (MOC strategy), however, the two processors communicated with each other and the amount of compression in a given frequency channel of each processor in the pair decreased with increases in the output energy from the contralateral processor. The analysis of output signals from the STD and MOC strategies suggests that in natural binaural listening, the MOCR possibly causes a small reduction of audibility but enhances frequency-specific inter-aural level differences and the segregation of spatially non-overlapping sound sources. The proposed MOC strategy could improve the performance of CI and hearing-aid users.

Priorities for hearing loss prevention and estimates of global cause-specific burdens of hearing loss: a systematic rapid review.

BACKGROUND: Hearing loss affects approximately 1·6 billion individuals worldwide. Many cases are preventable. We aimed to estimate the annual number of new hearing loss cases that could be attributed to meningitis, otitis media, congenital rubella syndrome, cytomegalovirus, and ototoxic medications, specifically aminoglycosides, platinum-based chemotherapeutics, and antimalarials. METHODS: We used a targeted and a rapid systematic literature review to calculate yearly global incidences of each cause of hearing loss. We estimated the prevalence of hearing loss for each presumed cause. For each cause, we calculated the global number of yearly hearing loss cases associated with the exposure by multiplying the estimated exposed population by the prevalence of hearing loss associated with the exposure, accounting for mortality when warranted. FINDINGS: An estimated 257·3 million people per year are exposed to these preventable causes of hearing loss, leading to an estimated 33·8 million new cases of hearing loss worldwide per year. Most hearing loss cases were among those with exposure to ototoxic medications (19·6 million [range 12·6 million-27·9 million] from short-course aminoglycoside therapy and 12·3 million from antimalarials). We estimated that 818 000 cases of hearing loss were caused by otitis media, 346 000 by meningitis, 114 000 by cytomegalovirus, and 59 000 by congenital rubella syndrome. INTERPRETATION: The global burden of preventable hearing loss is large. Hearing loss that is attributable to disease sequelae or ototoxic medications contributes substantially to the global burden of hearing loss. Prevention of these conditions should be a global health priority. FUNDING: The US National Institute on Deafness and Other Communication Disorders and the US National Institute on Aging.

Harnessing the Power of Artificial Intelligence in Otolaryngology and the Communication Sciences.

Use of artificial intelligence (AI) is a burgeoning field in otolaryngology and the communication sciences. A virtual symposium on the topic was convened from Duke University on October 26, 2020, and was attended by more than 170 participants worldwide. This review presents summaries of all but one of the talks presented during the symposium; recordings of all the talks, along with the discussions for the talks, are available at https://www.youtube.com/watch?v=ktfewrXvEFg and https://www.youtube.com/watch?v=-gQ5qX2v3rg . Each of the summaries is about 2500 words in length and each summary includes two figures. This level of detail far exceeds the brief summaries presented in traditional reviews and thus provides a more-informed glimpse into the power and diversity of current AI applications in otolaryngology and the communication sciences and how to harness that power for future applications.

Validation of the Decision model of the Burden of Hearing loss Across the Lifespan (DeciBHAL) in Chile, India, and Nigeria.

Background: There is no published decision model for informing hearing health care resource allocation across the lifespan in low- and middle-income countries. We sought to validate the Decision model of the Burden of Hearing loss Across the Lifespan International (DeciBHAL-I) in Chile, India, and Nigeria. Methods: DeciBHAL-I simulates bilateral sensorineural hearing loss (SNHL) and conductive hearing loss (CHL) acquisition, SNHL progression, and hearing loss treatment. To inform model inputs, we identified setting-specific estimates including SNHL prevalence from the Global Burden of Disease (GBD) studies, acute otitis media (AOM) incidence and prevalence of otitis-media related CHL from a systematic review, and setting-specific pediatric and adult hearing aid use prevalence. We considered a coefficient of variance root mean square error (CV-RMSE) of ≤15% to indicate good model fit. Findings: The model-estimated prevalence of bilateral SNHL closely matched GBD estimates, (CV-RMSEs: 3.2-7.4%). Age-specific AOM incidences from DeciBHAL-I also achieved good fit (CV-RMSEs=5.0-7.5%). Model-projected chronic suppurative otitis media prevalence (1.5% in Chile, 4.9% in India, and 3.4% in Nigeria) was consistent with setting-specific estimates, and the incidence of otitis media-related CHL was calibrated to attain adequate model fit. DeciBHAL-projected adult hearing aid use in Chile (3.2-19.7% ages 65-85 years) was within the 95% confidence intervals of published estimates. Adult hearing aid prevalence from the model in India was 1.4-2.3%, and 1.1-1.3% in Nigeria, consistent with literature-based and expert estimates. Interpretation: DeciBHAL-I reasonably simulates hearing loss natural history, detection, and treatment in Chile, India, and Nigeria. Future cost-effectiveness analyses might use DeciBHAL-I to inform global hearing health policy. Funding: National Institutes of Health (3UL1-TR002553-03S3 and F30 DC019846).

Development and validation of DeciBHAL-US: A novel microsimulation model of hearing loss across the lifespan in the United States.

BACKGROUND: Hearing loss affects over 50% of people in the US across their lifespan and there is a lack of decision modeling frameworks to inform optimal hearing healthcare delivery. Our objective was to develop and validate a microsimulation model of hearing loss across the lifespan in the US. METHODS: We collaborated with the Lancet Commission on Hearing Loss to outline model structure, identify input data sources, and calibrate/validate DeciBHAL-US (Decision model of the Burden of Hearing loss Across the Lifespan). We populated the model with literature-based estimates and validated the conceptual model with key informants. We validated key model endpoints to the published literature, including: 1) natural history of sensorineural hearing loss (SNHL), 2) natural history of conductive hearing loss (CHL), and 3) the hearing loss cascade of care. We reported the coefficient of variance root mean square error (CV-RMSE), considering values ≤15% to indicate adequate fit. FINDINGS: For SNHL prevalence, the CV-RMSE for model projected male and female age-specific prevalence compared to sex-adjusted National Health and Nutrition Examination Survey (NHANES) data was 4.9 and 5.7%, respectively. Incorporating literature-based age-related decline in SNHL, we validated mean four-frequency average hearing loss in the better ear (dB) among all persons to longitudinal data (CV-RMSE=11.3%). We validated the age-stratified prevalence of CHL to adjusted NHANES data (CV-RMSE=10.9%). We incorporated age- and severity-stratified time to first hearing aid (HA) use data and HA discontinuation data (adjusted for time-period of use) and validated to NHANES estimates on the prevalence of adult HA use (CV-RMSE=10.3%). INTERPRETATION: Our results indicate adequate model fit to internal and external validation data. Future incorporation of cost and severity-stratified utility data will allow for cost-effectiveness analysis of US hearing healthcare interventions across the lifespan. Further research might expand the modeling framework to international settings. FUNDING: This study was funded by the National Institute on Deafness and Other Communication Disorders and the National Institute on Aging (3UL1-TR002553-03S3 and F30 DC019846).

Challenges of the Deaf and Hearing Impaired in the Masked World of COVID-19.

Difficulties of the hearing impaired have increased due to COVID-19, leading to lack of inclusiveness along with the breakdown of their mental, physical, and social health. The study objective was to assess the challenges faced by the deaf and hearing-impaired people during COVID-19 by a literature review. Literature search was done using keywords such as "challenges" OR "barriers" and "COVID-19" OR "Deaf" OR "Hearing Impaired" OR "Communication" on PubMed and Google Scholar from November 2019 to June 2020. The challenges faced were lack of information, face mask making communication difficult, social distancing affecting their physical, mental health, stigma and barriers related to the health-care system. Strategies included use of technology, help from sign language instructors, and preparedness of health-care settings for the hearing disabled. System strengthening, tele-medicine, and policy amendments can be the pillars to build up the support system for the hearing impaired to protect them from COVID-19.

Evidence gaps in economic analyses of hearing healthcare: A systematic review.

BACKGROUND: Hearing loss is a common and costly medical condition. This systematic review sought to identify evidence gaps in published model-based economic analyses addressing hearing loss to inform model development for an ongoing Lancet Commission. METHODS: We searched the published literature through 14 June 2020 and our inclusion criteria included decision model-based cost-effectiveness analyses that addressed diagnosis, treatment, or prevention of hearing loss. Two investigators screened articles for inclusion at the title, abstract, and full-text levels. Data were abstracted and the studies were assessed for the qualities of model structure, data assumptions, and reporting using a previously published quality scale. FINDINGS: Of 1437 articles identified by our search, 117 unique studies met the inclusion criteria. Most of these model-based analyses were set in high-income countries (n = 96, 82%). The evaluated interventions were hearing screening (n = 35, 30%), cochlear implantation (n = 34, 29%), hearing aid use (n = 28, 24%), vaccination (n = 22, 19%), and other interventions (n = 29, 25%); some studies included multiple interventions. Eighty-six studies reported the main outcome in quality-adjusted or disability-adjusted life-years, 24 of which derived their own utility values. The majority of the studies used decision tree (n = 72, 62%) or Markov (n = 41, 35%) models. Forty-one studies (35%) incorporated indirect economic effects. The median quality rating was 92/100 (IQR:72-100). INTERPRETATION: The review identified a large body of literature exploring the economic efficiency of hearing healthcare interventions. However, gaps in evidence remain in evaluation of hearing healthcare in low- and middle-income countries, as well as in investigating interventions across the lifespan. Additionally, considerable uncertainty remains around productivity benefits of hearing healthcare interventions as well as utility values for hearing-assisted health states. Future economic evaluations could address these limitations. FUNDING: NCATS 3UL1-TR002553-03S3.

An attempt to improve bilateral cochlear implants by increasing the distance between electrodes and providing complementary information to the two ears.

OBJECTIVES: The purpose of this investigation was to determine if adult bilateral cochlear implant recipients could benefit from using a speech processing strategy in which the input spectrum was interleaved among electrodes across the two implants. DESIGN: Two separate experiments were conducted. In both experiments, subjects were tested using a control speech processing strategy and a strategy in which the full input spectrum was filtered so that only the output of half of the filters was audible to one implant, while the output of the alternative filters was audible to the other implant. The filters were interleaved in a way that created alternate frequency "holes" between the two cochlear implants. RESULTS: In experiment one, four subjects were tested on consonant recognition. Results indicated that one of the four subjects performed better with the interleaved strategy, one subject received a binaural advantage with the interleaved strategy that they did not receive with the control strategy, and two subjects showed no decrement in performance when using the interleaved strategy. In the second experiment, 11 subjects were tested on word recognition, sentences in noise, and localization (it should be noted that not all subjects participated in all tests). Results showed that for speech perception testing one subject achieved significantly better scores with the interleaved strategy on all tests, and seven subjects showed a significant improvement with the interleaved strategy on at least one test. Only one subject showed a decrement in performance on all speech perception tests with the interleaved strategy. Out of nine subjects, one subject preferred the sound quality of the interleaved strategy. No one performed better on localization with the interleaved strategy. CONCLUSION: Data from this study indicate that some adult bilateral cochlear implant recipients can benefit from using a speech processing strategy in which the input spectrum is interleaved among electrodes across the two implants. It is possible that the subjects in this study who showed a significant improvement with the interleaved strategy did so because of less channel interaction; however, this hypothesis was not directly tested.

Lateralization of virtual sound sources with a binaural cochlear-implant sound coding strategy inspired by the medial olivocochlear reflex.

Many users of bilateral cochlear implants (BiCIs) localize sound sources less accurately than do people with normal hearing. This may be partly due to using two independently functioning CIs with fixed compression, which distorts and/or reduces interaural level differences (ILDs). Here, we investigate the potential benefits of using binaurally coupled, dynamic compression inspired by the medial olivocochlear reflex; an approach termed "the MOC strategy" (Lopez-Poveda et al., 2016, Ear Hear 37:e138-e148). Twelve BiCI users were asked to localize wideband (125-6000 Hz) noise tokens in a virtual horizontal plane. Stimuli were processed through a standard (STD) sound processing strategy (i.e., involving two independently functioning sound processors with fixed compression) and three different implementations of the MOC strategy: one with fast (MOC1) and two with slower contralateral control of compression (MOC2 and MOC3). The MOC1 and MOC2 strategies had effectively greater inhibition in the higher than in the lower frequency channels, while the MOC3 strategy had slightly greater inhibition in the lower than in the higher frequency channels. Localization was most accurate with the MOC1 strategy, presumably because it provided the largest and less ambiguous ILDs. The angle error improved slightly from 25.3° with the STD strategy to 22.7° with the MOC1 strategy. The improvement in localization ability over the STD strategy disappeared when the contralateral control of compression was made slower, presumably because stimuli were too short (200 ms) for the slower contralateral inhibition to enhance ILDs. Results suggest that some MOC implementations hold promise for improving not only speech-in-noise intelligibility, as shown elsewhere, but also sound source lateralization.

Cochlear implants: a remarkable past and a brilliant future.

The aims of this paper are to (i) provide a brief history of cochlear implants; (ii) present a status report on the current state of implant engineering and the levels of speech understanding enabled by that engineering; (iii) describe limitations of current signal processing strategies; and (iv) suggest new directions for research. With current technology the "average" implant patient, when listening to predictable conversations in quiet, is able to communicate with relative ease. However, in an environment typical of a workplace the average patient has a great deal of difficulty. Patients who are "above average" in terms of speech understanding, can achieve 100% correct scores on the most difficult tests of speech understanding in quiet but also have significant difficulty when signals are presented in noise. The major factors in these outcomes appear to be (i) a loss of low-frequency, fine structure information possibly due to the envelope extraction algorithms common to cochlear implant signal processing; (ii) a limitation in the number of effective channels of stimulation due to overlap in electric fields from electrodes; and (iii) central processing deficits, especially for patients with poor speech understanding. Two recent developments, bilateral implants and combined electric and acoustic stimulation, have promise to remediate some of the difficulties experienced by patients in noise and to reinstate low-frequency fine structure information. If other possibilities are realized, e.g., electrodes that emit drugs to inhibit cell death following trauma and to induce the growth of neurites toward electrodes, then the future is very bright indeed.

Bilaterally Combined Electric and Acoustic Hearing in Mandarin-Speaking Listeners: The Population With Poor Residual Hearing.

The hearing loss criterion for cochlear implant candidacy in mainland China is extremely stringent (bilateral severe to profound hearing loss), resulting in few patients with substantial residual hearing in the nonimplanted ear. The main objective of the current study was to examine the benefit of bimodal hearing in typical Mandarin-speaking implant users who have poorer residual hearing in the nonimplanted ear relative to those used in the English-speaking studies. Seventeen Mandarin-speaking bimodal users with pure-tone averages of ∼80 dB HL participated in the study. Sentence recognition in quiet and in noise as well as tone and word recognition in quiet were measured in monaural and bilateral conditions. There was no significant bimodal effect for word and sentence recognition in quiet. Small bimodal effects were observed for sentence recognition in noise (6%) and tone recognition (4%). The magnitude of both effects was correlated with unaided thresholds at frequencies near voice fundamental frequencies (F0s). A weak correlation between the bimodal effect for word recognition and unaided thresholds at frequencies higher than F0s was identified. These results were consistent with previous findings that showed more robust bimodal benefits for speech recognition tasks that require higher spectral resolution than speech recognition in quiet. The significant but small F0-related bimodal benefit was also consistent with the limited acoustic hearing in the nonimplanted ear of the current subject sample, who are representative of the bimodal users in mainland China. These results advocate for a more relaxed implant candidacy criterion to be used in mainland China.

The surprising performance of present-day cochlear implants.

The speech reception performance of a recipient of the Clarion CII implant was evaluated with a comprehensive set of tests. The same tests were administered for a group of six subjects with normal hearing. Scores for the implant subject were not different from the scores for the normal-hearing subjects, for seven of the nine tests, including the most difficult test used in standard clinical practice. These results are both surprising and encouraging, in that the implant provides only a very crude mimicking of only some aspects of the normal physiology.

Design for a simplified cochlear implant system.

A simplified cochlear implant (CI) system would be appropriate for widespread use in developing countries. Here, we describe a CI that we have designed to realize such a concept. The system implements 8 channels of processing and stimulation using the continuous interleaved sampling (CIS) strategy. A generic digital signal processing (DSP) chip is used for the processing, and the filtering functions are performed with a fast Fourier transform (FFT) of a microphone or other input. Data derived from the processing are transmitted through an inductive link using pulse width modulation (PWM) encoding and amplitude shift keying (ASK) modulation. The same link is used in the reverse direction for backward telemetry of electrode and system information. A custom receiver-stimulator chip has been developed that demodulates incoming data using pulse counting and produces charge balanced biphasic pulses at 1000 pulses/s/electrode. This chip is encased in a titanium package that is hermetically sealed using a simple but effective method. A low cost metal-silicon hybrid mold has been developed for fabricating an intracochlear electrode array with 16 ball-shaped stimulating contacts.