A narrative review of the logistic and economic feasibility of cochlear implants in lower-income countries

Cochlear implants and deafness: a global case study to increase policy awareness and action on an under-resourced health issue

There has been a major growth in global health networks in recent decades to address health issues including tobacco use, alcohol abuse, and maternal mortality. Most conditions that incur high costs have provoked networks of advocates working to mitigate the impact, increase investment in research, and establish campaigns. Global health networks often work simultaneously across policy, knowledge creation, and advocacy. Until recently there has been limited activity in global health networks and advocacy addressing hearing loss and deafness which has contributed to its relatively low visibility with policymakers compared to other health conditions. This discussion paper reports on a global consultation that explored the views of advocacy groups and individuals on advocacy for the management of hearing loss, and cochlear implantation (CI). It focussed on stakeholders' views of current advocacy endeavours, opportunities and barriers, and the possible development of a global advocacy network to improve access to cochlear implantation and the supporting services. The subsequent development of a global health network, the Cochlear Implant International Community of Action (CIICA) is discussed and the conditions necessary for the successful development of health networks are explored. This paper will be of interest to those wishing to understand the factors influencing the development of health networks and advocacy.

Improved tactile speech perception and noise robustness using audio-to-tactile sensory substitution with amplitude envelope expansion

Recent advances in haptic technology could allow haptic hearing aids, which convert audio to tactile stimulation, to become viable for supporting people with hearing loss. A tactile vocoder strategy for audio-to-tactile conversion, which exploits these advances, has recently shown significant promise. In this strategy, the amplitude envelope is extracted from several audio frequency bands and used to modulate the amplitude of a set of vibro-tactile tones. The vocoder strategy allows good consonant discrimination, but vowel discrimination is poor and the strategy is susceptible to background noise. In the current study, we assessed whether multi-band amplitude envelope expansion can effectively enhance critical vowel features, such as formants, and improve speech extraction from noise. In 32 participants with normal touch perception, tactile-only phoneme discrimination with and without envelope expansion was assessed both in quiet and in background noise. Envelope expansion improved performance in quiet by 10.3% for vowels and by 5.9% for consonants. In noise, envelope expansion improved overall phoneme discrimination by 9.6%, with no difference in benefit between consonants and vowels. The tactile vocoder with envelope expansion can be deployed in real-time on a compact device and could substantially improve clinical outcomes for a new generation of haptic hearing aids.

Familial psychosocial impact of cochlear implantation

BACKGROUND

Adult cochlear implantation rates are increasing, and the resulting change in hearing capabilities has vast impacts in the psychosocial domain of life for the cochlear implant users and their families. However, there is currently no published evidence synthesis of the ways in which adult cochlear implantation affects the psychosocial sphere of the family unit.

OBJECTIVE

(1) Describe the existing literature on the psychosocial impact of cochlear implantation on adults. (2) Assess the range of impacts on the family unit and highlight areas warranting further investigation.

DATA SOURCES

Ovid, CINAHL, and Scopus.

REVIEW METHODS

Databases were systematically searched from January 1, 2007 to May 1, 2022. Eligibility assessment was performed via two independent investigators. Disagreements in selection were discussed and consulted on with a third investigator as needed.

RESULTS

Of the 875 unique articles identified, 13 remained in the final review. The most frequently noted psychosocial impacts on the family was quality of life (100 %), family relations (85 %), conversational access (85 %), everyday hearing (77 %), and less feelings of isolation (77 %). 6 of the studies only considered the viewpoint of the CI user and did not have a congruent survey response from an individual from their family unit.

CONCLUSION

This study describes the existing literature on the familial psychosocial impact of adult cochlear implantation, focusing on the general well-being, social integration, and psychological aspects noted post-implantation. This review identifies gaps in this research, with large numbers of studies on CI user benefits and little insight into the impact on the family unit. We recommend shifting research on CI impact toward a focus on the family unit, rather than individual, and an evaluation of familial influence in electing to receive a CI.

Improved tactile speech perception using audio-to-tactile sensory substitution with formant frequency focusing

Haptic hearing aids, which provide speech information through tactile stimulation, could substantially improve outcomes for both cochlear implant users and for those unable to access cochlear implants. Recent advances in wide-band haptic actuator technology have made new audio-to-tactile conversion strategies viable for wearable devices. One such strategy filters the audio into eight frequency bands, which are evenly distributed across the speech frequency range. The amplitude envelopes from the eight bands modulate the amplitudes of eight low-frequency tones, which are delivered through vibration to a single site on the wrist. This tactile vocoder strategy effectively transfers some phonemic information, but vowels and obstruent consonants are poorly portrayed. In 20 participants with normal touch perception, we tested (1) whether focusing the audio filters of the tactile vocoder more densely around the first and second formant frequencies improved tactile vowel discrimination, and (2) whether focusing filters at mid-to-high frequencies improved obstruent consonant discrimination. The obstruent-focused approach was found to be ineffective. However, the formant-focused approach improved vowel discrimination by 8%, without changing overall consonant discrimination. The formant-focused tactile vocoder strategy, which can readily be implemented in real time on a compact device, could substantially improve speech perception for haptic hearing aid users.

Experiences of parents of children with cochlear implants in South Africa: an exploratory study

PURPOSE

Cochlear implantation is a well-established option for early intervention. Children with hearing impairment and their parents are users of intervention services, with parents being more suited to provide insight into their experiences. The purpose of the current study was to describe the experiences of parents of children with cochlear implants (CIs) in the South African context.

METHODS

A qualitative research design was employed. Non-probability, purposive sampling was used. Seven, online semi-structured interviews were conducted with parents of children with CIs. Data were analysed using inductive thematic analysis.

RESULTS

Participants expressed feelings of certainty and assurance in the CI journey. Participants extended gratitude to the healthcare professionals involved in their children's CI journey. Feelings of doubt and stress were noted when coming to terms with the decision of cochlear implantation and financial stressors were noted as a challenge. Many participants found it challenging transitioning their children into school.

CONCLUSIONS

Parents conveyed having no regrets with their decision of cochlear implantation for their child and were grateful for the support provided by healthcare professionals. However, financial, and educational challenges remain. Findings suggest the need for more financial support for cochlear implantation in South Africa, and for adequate inclusive educational settings.

A country-wide health policy in Chile for deaf adults using cochlear implants: Analysis of health determinants and social impacts

BACKGROUND

Post-lingual deafness represents a critical challenge for adults' well-being with substantial public health burdens. One treatment of choice has been cochlear implants (CI) for people with severe to profound hearing loss (HL). Since 2018, Chile has implemented a high-cost policy to cover CI treatment, the "Ley Ricarte Soto" (LRS) health policy. However, wide variability exists in the use of this device. To date, no related study has been published on policy evaluation in Chile or other Latin American countries.

OBJECTIVES

This study aimed to evaluate the impact of the LRS policy on the treatment success and labour market inclusion among deaf or hard of hearing (DHH) adults using CI. We examined and characterised outcomes based on self-reports about treatment success and occupation status between 2018 and 2020.

DESIGN

We performed a prospective study using hospital clinical records and an online questionnaire with 76 DHH adults aged >15 who had received CIs since the introduction of the LRS policy in 2018. Using univariate and multivariate regression models, we investigated the relationship between demographic, audiological, and social determinants of health and outcomes, including treatment success for social inclusion (International Outcome inventory for Hearing Aids and CIs assessment: IOI-HA) and occupation status for labour market inclusion.

RESULTS

Our study showed elevated levels of treatment success in most of the seven sub-scores of the IOI-HA assessment. Similarly, around 70% of participants maintained or improved their occupations after receiving their CI. We found a significant positive association between treatment success and market inclusion. Participants diagnosed at younger ages had better results than older participants in both outcomes. Regarding social determinants of health, findings suggested participants with high social health insurance and a shorter commute time to the clinic had better results in treatment success. For labour market inclusion, participants with high education levels and better pre- CI occupation had better post-CI occupation status.

CONCLUSIONS

In evaluating the LRS policy for providing CIs for DHH adults in Chile, we found positive effects relating to treatment success and occupation status. Our study supports the importance of age at diagnosis and social determinants of health, which should be assessed by integrating public services and bringing them geographically closer to each beneficiary. Although evidence-based guidelines for candidate selection given by the LRS policy might contribute to good results, these guidelines could limit the policy access to people who do not meet the requirements of the guidelines due to social inequalities.

Assessing the manufacturable 32-channel cochlear electrode array: evaluation results for clinical trials

Reliability evaluation results of a manufacturable 32-channel cochlear electrode array are reported in this paper. Applying automated laser micro-machining process and a layer-by-layer silicone deposition scheme, authors developed the manufacturing methods of the electrode array for fine patterning and mass production. The developed electrode array has been verified through the requirements specified by the ISO Standard 14708-7. And the insertion trauma of the electrode array has been evaluated based on human temporal bone studies. According to the specified requirements, the electrode array was assessed through elongation & insulation, flexural, and fatigue tests. In addition, Temporal bone study was performed using eight fresh-frozen cadaver temporal bones with the electrode arrays inserted via the round window. Following soaking in saline condition, the impedances between conducting wires of the electrode array were measured over 100 kΩ (the pass/fail criterion). After each required test, it was shown that the electrode array maintained the electrical continuity and insulation condition. The average insertion angle of the electrode array inside the scala tympani was 399.7°. The human temporal bone studies exhibited atraumatic insertion rate of 60.3% (grade 0 or 1). The reliability of the manufacturable electrode array is successfully verified in mechanical, electrical, and histological aspects. Following the completion of a 32-channel cochlear implant system, the performance and stability of the 32-channel electrode array will be evaluated in clinical trials.

Improving speech perception for hearing-impaired listeners using audio-to-tactile sensory substitution with multiple frequency channels

Cochlear implants (CIs) have revolutionised treatment of hearing loss, but large populations globally cannot access them either because of disorders that prevent implantation or because they are expensive and require specialist surgery. Recent technology developments mean that haptic aids, which transmit speech through vibration, could offer a viable low-cost, non-invasive alternative. One important development is that compact haptic actuators can now deliver intense stimulation across multiple frequencies. We explored whether these multiple frequency channels can transfer spectral information to improve tactile phoneme discrimination. To convert audio to vibration, the speech amplitude envelope was extracted from one or more audio frequency bands and used to amplitude modulate one or more vibro-tactile tones delivered to a single-site on the wrist. In 26 participants with normal touch sensitivity, tactile-only phoneme discrimination was assessed with one, four, or eight frequency bands. Compared to one frequency band, performance improved by 5.9% with four frequency bands and by 8.4% with eight frequency bands. The multi-band signal-processing approach can be implemented in real-time on a compact device, and the vibro-tactile tones can be reproduced by the latest compact, low-powered actuators. This approach could therefore readily be implemented in a low-cost haptic hearing aid to deliver real-world benefits.

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.

Influencing discussions and use of neuroadvancements as professionals and citizens: Perspectives of Canadian speech-language pathologists and audiologists

BACKGROUND: Early involvement of stakeholders in neuroethics and neurogovernance discourses of neuroscientific and neurotechnological advancements is seen as essential to curtail negative consequences. Speech-language pathologists (SLPs) and audiologists (AUs) make use of neuroadvancements including cochlear implants, brain-computer interfaces, and deep-brain stimulation. Although they have a stake in neuroethics and neurogovernance discussions, they are rarely mentioned in having a role, whether as professionals or as citizens. OBJECTIVE: The objective of the study was to explore the role of SLPs and AUs as professionals and citizens in neuroethics and neurogovernance discussions and examine the utility of lifelong learning mechanisms to learn about the implications of neuroadvancements to contribute in a meaningful way to these discussions. METHODS: Semi-structured interviews conducted with 7 SLPs and 3 AUs were analyzed using thematic analysis. RESULTS: Participants stated that their roles expected from them as professionals and as citizens indicate the importance to be knowledgeable on ethical, legal, and social implications of neuroadvancements and that lifelong learning is not used to learn about these implications. CONCLUSION: More must be done to facilitate the participation of SLPs and AUs in neuroethics and neurogovernance discussions, which would enrich the neuroethics and neurogovernance discourses benefitting patients, professionals, and the public.

Manufacturable 32-Channel Cochlear Electrode Array and Preliminary Assessment of Its Feasibility for Clinical Use

(1) Background: In this study, we introduce a manufacturable 32-channel cochlear electrode array. In contrast to conventional cochlear electrode arrays manufactured by manual processes that consist of electrode-wire welding, the placement of each electrode, and silicone molding over wired structures, the proposed cochlear electrode array is manufactured by semi-automated laser micro-structuring and a mass-produced layer-by-layer silicone deposition scheme similar to the semiconductor fabrication process. (2) Methods: The proposed 32-channel electrode array has 32 electrode contacts with a length of 24 mm and 0.75 mm spacing between contacts. The width of the electrode array is 0.45 mm at its apex and 0.8 mm at its base, and it has a three-layered arrangement consisting of a 32-channel electrode layer and two 16-lead wire layers. To assess its feasibility, we conducted an electrochemical evaluation, stiffness measurements, and insertion force measurements. (3) Results: The electrochemical impedance and charge storage capacity are 3.11 ± 0.89 kOhm at 1 kHz and 5.09 mC/cm2, respectively. The V/H ratio, which indicates how large the vertical stiffness is compared to the horizontal stiffness, is 1.26. The insertion force is 17.4 mN at 8 mm from the round window, and the maximum extraction force is 61.4 mN. (4) Conclusions: The results of the preliminary feasibility assessment of the proposed 32-channel cochlear electrode array are presented. After further assessments are performed, a 32-channel cochlear implant system consisting of the proposed 32-channel electrode array, 32-channel neural stimulation and recording IC, titanium-based hermetic package, and sound processor with wireless power and signal transmission coil will be completed.

Electro-Haptic Stimulation: A New Approach for Improving Cochlear-Implant Listening

Cochlear implants (CIs) have been remarkably successful at restoring speech perception for severely to profoundly deaf individuals. Despite their success, several limitations remain, particularly in CI users' ability to understand speech in noisy environments, locate sound sources, and enjoy music. A new multimodal approach has been proposed that uses haptic stimulation to provide sound information that is poorly transmitted by the implant. This augmenting of the electrical CI signal with haptic stimulation (electro-haptic stimulation; EHS) has been shown to improve speech-in-noise performance and sound localization in CI users. There is also evidence that it could enhance music perception. We review the evidence of EHS enhancement of CI listening and discuss key areas where further research is required. These include understanding the neural basis of EHS enhancement, understanding the effectiveness of EHS across different clinical populations, and the optimization of signal-processing strategies. We also discuss the significant potential for a new generation of haptic neuroprosthetic devices to aid those who cannot access hearing-assistive technology, either because of biomedical or healthcare-access issues. While significant further research and development is required, we conclude that EHS represents a promising new approach that could, in the near future, offer a non-invasive, inexpensive means of substantially improving clinical outcomes for hearing-impaired individuals.

Sensitivity to Haptic Sound-Localization Cues at Different Body Locations

Cochlear implants (CIs) recover hearing in severely to profoundly hearing-impaired people by electrically stimulating the cochlea. While they are extremely effective, spatial hearing is typically severely limited. Recent studies have shown that haptic stimulation can supplement the electrical CI signal (electro-haptic stimulation) and substantially improve sound localization. In haptic sound-localization studies, the signal is extracted from the audio received by behind-the-ear devices and delivered to each wrist. Localization is achieved using tactile intensity differences (TIDs) across the wrists, which match sound intensity differences across the ears (a key sound localization cue). The current study established sensitivity to across-limb TIDs at three candidate locations for a wearable haptic device, namely: the lower tricep and the palmar and dorsal wrist. At all locations, TID sensitivity was similar to the sensitivity to across-ear intensity differences for normal-hearing listeners. This suggests that greater haptic sound-localization accuracy than previously shown can be achieved. The dynamic range was also measured and far exceeded that available through electrical CI stimulation for all of the locations, suggesting that haptic stimulation could provide additional sound-intensity information. These results indicate that an effective haptic aid could be deployed for any of the candidate locations, and could offer a low-cost, non-invasive means of improving outcomes for hearing-impaired listeners.

The inaugural World Report on Hearing: From barriers to a platform for change

The inaugural World Report on Hearing was recently published by the World Health Organisation, and outlines the burden of hearing loss, and strategies to overcome this through preventative and public health approaches. Here, we identify barriers to wide-scale adoption, including historic low prioritisation of hearing loss against other public health needs, a lack of a health workforce with relevant training, poor access to assistive technology, and individual and community-level stigma and misunderstanding. Overcoming these barriers will require multi-sector stakeholder collaboration, involving ear and hearing care professionals, patients, communities, industry and policymakers.