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.

Longitudinal urinary neopterin is associated with hearing threshold change over time in independent older adults.

Low-grade chronic inflammation is associated with many age-related conditions. Non-invasive methods to monitor low-grade chronic inflammation may improve the management of older people at risk of poorer outcomes. This longitudinal cohort study has determined baseline inflammation using neopterin volatility in monthly urine samples of 45 independent older adults (aged 65-75 years). Measurement of neopterin, an inflammatory metabolite, enabled stratification of individuals into risk categories based on how often in a 12-month period their neopterin level was raised. Hearing was measured (pure-tone audiometry) at baseline, 1 year and 3 years of the study. Results show that those in the highest risk category (neopterin raised greater than 50% of the time) saw greater deterioration, particularly in high-frequency, hearing. A one-way Welch's ANOVA showed a significant difference between the risk categories for change in high-frequency hearing (W (3, 19.6) = 9.164, p = 0.0005). Despite the study size and duration individuals in the highest risk category were more than twice as likely to have an additional age-related morbidity than those in the lowest risk category. We conclude that volatility of neopterin in urine may enable stratification of those at greatest risk of progression of hearing loss.

Integrated bimodal fitting and binaural streaming technology outcomes for unilateral cochlear implant users.

OBJECTIVE: Adults typically receive only one cochlear implant (CI) due to cost constraints, with a contralateral hearing aid recommended when there is aidable hearing. Standard hearing aids differ from a CI in terms of processing strategy and function as a separate entity, requiring the user to integrate the disparate signals. Integrated bimodal technology has recently been introduced to address this challenge. The aim of the study was to investigate the performance of unilateral CI users with and without an integrated bimodal fitting and determine whether binaural streaming technology offers additional benefit. STUDY SAMPLE: Twenty-six CI users using integrated bimodal technology. DESIGN: Repeated measures where outcomes and user experience were assessed using a functional test battery more representative of real life listening (speech perception in noise tests, localisation test, tracking test) and the speech, spatial and qualities-of-hearing scale (SSQ). RESULTS: Bimodal outcomes were significantly better than for CI alone. Speech perception in noise improvements ranged from 1.4 dB to 3.5 dB depending on the location of speech and noise. The localisation and tracking tests, and the SSQ also showed significant improvements. Binaural streaming offered additional improvement (1.2 dB to 6.1 dB on the different speech tests). CONCLUSIONS: Integrated bimodal and binaural streaming technology improved the performance of unilateral CI users.

Improved tactile speech robustness to background noise with a dual-path recurrent neural network noise-reduction method.

Many people with hearing loss struggle to understand speech in noisy environments, making noise robustness critical for hearing-assistive devices. Recently developed haptic hearing aids, which convert audio to vibration, can improve speech-in-noise performance for cochlear implant (CI) users and assist those unable to access hearing-assistive devices. They are typically body-worn rather than head-mounted, allowing additional space for batteries and microprocessors, and so can deploy more sophisticated noise-reduction techniques. The current study assessed whether a real-time-feasible dual-path recurrent neural network (DPRNN) can improve tactile speech-in-noise performance. Audio was converted to vibration on the wrist using a vocoder method, either with or without noise reduction. Performance was tested for speech in a multi-talker noise (recorded at a party) with a 2.5-dB signal-to-noise ratio. An objective assessment showed the DPRNN improved the scale-invariant signal-to-distortion ratio by 8.6 dB and substantially outperformed traditional noise-reduction (log-MMSE). A behavioural assessment in 16 participants showed the DPRNN improved tactile-only sentence identification in noise by 8.2%. This suggests that advanced techniques like the DPRNN could substantially improve outcomes with haptic hearing aids. Low-cost haptic devices could soon be an important supplement to hearing-assistive devices such as CIs or offer an alternative for people who cannot access CI technology.

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.

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.

Macrophages in the cochlea; an immunological link between risk factors and progressive hearing loss.

Macrophages are abundant in the cochlea; however, their role in hearing loss is not well understood. Insults to the cochlea, such as noise or insertion of a cochlear implant, cause an inflammatory response, which includes activation of tissue-resident macrophages. Activation is characterized by changes in macrophage morphology, mediator expression, and distribution. Evidence from other organs shows activated macrophages can become primed, whereby subsequent insults cause an elevated inflammatory response. Primed macrophages in brain pathologies respond to circulating inflammatory mediators by disproportionate synthesis of inflammatory mediators. This signaling occurs behind an intact blood-brain barrier, similar to the blood-labyrinth barrier in the cochlea. Local tissue damage can occur as the result of mediator release by activated macrophages. Damage is typically localized; however, if it is to structures with limited ability to repair, such as neurons or hair cells within the cochlea, it is feasible that this contributes to the progressive loss of function seen in hearing loss. We propose that macrophages in the cochlea link risk factors and hearing loss. Injury to the cochlea causes local macrophage activation that typically resolves. However, in susceptible individuals, some macrophages enter a primed state. Once primed, these macrophages can be further activated, as a consequence of circulating inflammatory molecules associated with common co-morbidities. Hypothetically, this would lead to further cochlear damage and loss of hearing. We review the evidence for the role of tissue-resident macrophages in the cochlea and propose that cochlear macrophages contribute to the trajectory of hearing loss and warrant further study.

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.

Inflammation at the Tissue-Electrode Interface in a Case of Rapid Deterioration in Hearing Performance Leading to Explant After Cochlear Implantation.

OBJECTIVE: The reasons for soft failure after cochlear implantation require investigation. This study proposes a method to study and characterize the tissue response to the array in a case of soft failure in a person undergoing reimplantation. CASE: The woman in her 50s, with an underlying autoimmune condition, received a cochlear implant using hearing preservation technique after developing profound hearing loss more than 2 kHz with a moderate loss of less than 500 Hz over a 10-year period. The case was identified as a soft failure due to deteriorating performance, discomfort, and migration over the 10 months after implantation. Impedance telemetry, speech perception measures, and audiometric thresholds are described. At explantation there was evidence of fibrosis. INTERVENTIONS: To use histology and immunohistochemistry to determine the cellular response of the tissue associated with the electrode array at time of explantation. MAIN OUTCOME MEASURES: Identification of the cell types, regional variations, and inflammatory marker expression in the fibrotic tissue associated with the array. RESULTS: Neutrophils and eosinophils were identified, along with a variable pattern of collagen deposition. CD68 and CD163-positive macrophages and T cells were variably distributed through the tissue and interleukin-1 beta and vascular endothelial growth factor receptor-2 expression was identified. CONCLUSIONS: The expression profile is evidence of active inflammation in the tissue despite the time since implantation. This study is the first to characterize the tissue response to the array in a person undergoing reimplantation, and who can be followed to determine the individual response to arrays. It establishes that the investigation of explanted devices after soft-failure is feasible.

Piloting the recording of electrode voltages (REVS) using surface electrodes as a test to identify cochlear implant electrode migration, extra-cochlear electrodes and basal electrodes causing discomfort.

OBJECTIVES: To determine if Electrode Voltage (EV) measurements are potentially suitable as a test for detecting extra-cochlear electrodes in cochlear implants (CIs). METHODS: EV measurements were made using surface electrodes in live mode in 17 adult cochlear implant (CI) users. Repeatability, the effects of stimulation level, CI active electrode position, (active) recording electrode position and stimulation mode (for Nucleus devices) were investigated. RESULTS/DISCUSSION: Recordings made in monopolar mode showed good repeatability when the active recording electrode was placed on the ipsilateral earlobe; voltages increased linearly with stimulation level as expected. EVs for basal electrodes differed greatly between partially inserted/migrated devices, fully inserted devices with all electrodes activated, and those with deactivated basal electrodes [χ2(2) = 10.2, p < 0.05 for the most basal electrode]. EVs for Nucleus devices were small for electrodes on the array when compared to those for monopolar return electrodes, except for the participant with extra-cochlear electrodes. We argue that fibrosis around the electrode array facilitated current flow across the round window in this case. CONCLUSION: The test appears to be a viable approach to detect electrode migration and extra-cochlear electrodes in adult CI users and may also be sensitive to discomfort caused by current leakage from the basal end of the cochlea.

Hearing impairment after subarachnoid hemorrhage.

Background: Subarachnoid hemorrhage (SAH) survivors experience significant neurological disability, some of which is under-recognized by neurovascular clinical teams. We set out to objectively determine the occurrence of hearing impairment after SAH, characterize its peripheral and/or central origin, and investigate likely pathological correlates. Methods: In a case-control study (n = 41), participants were asked about new onset hearing difficulty 3 months post-SAH, compared with pre-SAH. Formal audiological assessment included otoscopy, pure tone audiometry, a questionnaire identifying symptoms of peripheral hearing loss and/or auditory processing disorder, and a test of speech understanding in noise. A separate cohort (n = 21) underwent quantitative susceptibility mapping (QSM) of the auditory cortex 6 months after SAH, for correlation with hearing difficulty. Results: Twenty three percent of SAH patients reported hearing difficulty that was new in onset post-SAH. SAH patients had poorer pure tone thresholds compared to controls. The proportion of patients with peripheral hearing loss as defined by the World Health Organization and British Audiological Society was however not increased, compared to controls. All SAH patients experienced symptoms of auditory processing disorder post-SAH, with speech-in-noise test scores significantly worse versus controls. Iron deposition in the auditory cortex was higher in patients reporting hearing difficulty versus those who did not. Conclusion: This study firmly establishes hearing impairment as a frequent clinical feature after SAH. It primarily consists of an auditory processing disorder, mechanistically linked to iron deposition in the auditory cortex. Neurovascular teams should inquire about hearing, and refer SAH patients for audiological assessment and management.

Exploiting Routine Clinical Measures to Inform Strategies for Better Hearing Performance in Cochlear Implant Users.

Neuroprostheses designed to interface with the nervous system to replace injured or missing senses can significantly improve a patient's quality of life. The challenge remains to provide implants that operate optimally over several decades. Changes in the implant-tissue interface may precede performance problems. Tools to identify and characterize such changes using existing clinical measures would be highly valuable. Modern cochlear implant (CI) systems allow easy and regular measurements of electrode impedance (EI). This measure is routinely performed as a hardware integrity test, but it also allows a level of insight into the immune-mediated response to the implant, which is associated with performance outcomes. This study is a 5-year retrospective investigation of MED-EL CI users at the University of Southampton Auditory Implant Service including 176 adult ears (18-91) and 74 pediatric ears (1-17). The trend in EI in adults showed a decrease at apical electrodes. An increase was seen at the basal electrodes which are closest to the surgery site. The trend in the pediatric cohort was increasing EI over time for nearly all electrode positions, although this group showed greater variability and had a smaller sample size. We applied an outlier-labeling rule to statistically identify individuals that exhibit raised impedance. This highlighted 14 adult ears (8%) and 3 pediatric ears (5%) with impedance levels that deviated from the group distribution. The slow development of EI suggests intra-cochlear fibrosis and/or osteogenesis as the underlying mechanism. The usual clinical intervention for extreme impedance readings is to deactivate the relevant electrode. Our findings highlight some interesting clinical contradictions: some cases with raised (but not extreme) impedance had not prompted an electrode deactivation; and many cases of electrode deactivation had been informed by subjective patient reports. This emphasizes the need for improved objective evidence to inform electrode deactivations in borderline cases, for which our outlier-labeling approach is a promising candidate. A data extraction and analysis protocol that allows ongoing and automated statistical analysis of routinely collected data could benefit both the CI and wider neuroprosthetics communities. Our approach provides new tools to inform practice and to improve the function and longevity of neuroprosthetic devices.

A Music-Related Quality of Life Measure to Guide Music Rehabilitation for Adult Cochlear Implant Users.

PURPOSE: A music-related quality of life (MuRQoL) questionnaire was developed for the evaluation of music rehabilitation for adult cochlear implant (CI) users. The present studies were aimed at refinement and validation. METHOD: Twenty-four experts reviewed the MuRQoL items for face validity. A refined version was completed by 147 adult CI users, and psychometric techniques were used for item selection, assessment of reliability, and definition of the factor structure. The same participants completed the Short Form Health Survey for construct validation. MuRQoL responses from 68 CI users were compared with those of a matched group of adults with normal hearing. RESULTS: Eighteen items measuring music perception and engagement and 18 items measuring their importance were selected; they grouped together into 2 domains. The final questionnaire has high internal consistency and repeatability. Significant differences between CI users and adults with normal hearing and a correlation between music engagement and quality of life support construct validity. Scores of music perception and engagement and importance for the 18 items can be combined to assess the impact of music on the quality of life. CONCLUSION: The MuRQoL questionnaire is a reliable and valid measure of self-reported music perception, engagement, and their importance for adult CI users with potential to guide music aural rehabilitation.

Exploring the experiences of teenagers with cochlear implants.

OBJECTIVES: Teenage cochlear implant users' perceptions of deafness, surgery, fitting of the device and life as a cochlear implant wearer were explored in order to gain a more comprehensive understanding of teenagers' experiences of living with the device. METHODS: Semi-structured in-depth interviews were undertaken and analysed using thematic analysis. Ten teenagers aged 14-16 years with at least one cochlear implant were interviewed. RESULTS: Seven teenagers experienced great pre-operative anxiety and two reported significant post-operative pain. Four of the teenagers described a mismatch between their expectations and the disappointing reality of adjusting to the device. However, all the teenagers reported an enhanced sense of well-being as a result of being able to interact more easily with their world around them. The teenagers differed in the extent to which they identified with the hearing and deaf world. DISCUSSION: Despite the early challenges, over time the teenagers experienced many functional and psychosocial benefits. Most felt their lives were now easier as a result of the cochlear implant(s). They described complex, flexible identities. CONCLUSIONS: By giving prominence to the teenagers' voices this study has added new knowledge concerning their experience of surgery. The findings also more fully revealed the challenges of adjusting to the device and the impact of having a cochlear implant on the teenagers' identities. Clinical recommendations are made to address the gaps in service highlighted by these findings.

Modelling the effect of round window stiffness on residual hearing after cochlear implantation.

Preservation of residual hearing after cochlear implantation is now considered an important goal of surgery. However, studies indicate an average post-operative hearing loss of around 20 dB at low frequencies. One factor which may contribute to post-operative hearing loss, but which has received little attention in the literature to date, is the increased stiffness of the round window, due to the physical presence of the cochlear implant, and to its subsequent thickening or to bone growth around it. A finite element model was used to estimate that there is approximately a 100-fold increase in the round window stiffness due to a cochlear implant passing through it. A lumped element model was then developed to study the effects of this change in stiffness on the acoustic response of the cochlea. As the round window stiffness increases, the effects of the cochlear and vestibular aqueducts become more important. An increase of round window stiffness by a factor of 10 is predicted to have little effect on residual hearing, but increasing this stiffness by a factor of 100 reduces the acoustic sensitivity of the cochlea by about 20 dB, below 1 kHz, in reasonable agreement with the observed loss in residual hearing after implantation. It is also shown that the effect of this stiffening could be reduced by incorporating a small gas bubble within the cochlear implant.

Robustness against distortion of fundamental frequency cues in simulated electro-acoustic hearing.

Speech recognition by cochlear implant users can be improved by adding an audible low frequency acoustic signal to electrical hearing; the resulting improvement is deemed "electro-acoustic stimulation (EAS) benefit." However, a crucial low frequency cue, fundamental frequency (F0), can be distorted via the impaired auditory system. In order to understand how F0 distortions may affect EAS benefit, normal-hearing listeners were presented monaurally with vocoded speech (frequencies >250 Hz) and an acoustical signal (frequencies <250 Hz) with differing manipulations of the F0 signal, specifically: a pure tone with the correct mean F0 but with smaller variations around this mean, or a narrowband of white noise centered around F0, at varying bandwidths; a pure tone down-shifted in frequency by 50 Hz but keeping overall frequency modulations. Speech-recognition thresholds improved when tones with reduced frequency modulation were presented, and improved significantly for noise bands maintaining F0 information. A down-shifted tone, or only a tone to indicate voicing, showed no EAS benefit. These results confirm that the presence of the target's F0 is beneficial for EAS hearing in a noisy environment, and they indicate that the benefit is robust to F0 distortion, as long as the mean F0 and frequency modulations of F0 are preserved.

Preliminary assessment of the feasibility of using AB words to assess candidacy in adults.

BACKGROUND: Adult cochlear implant (CI) candidacy is assessed in part by the use of speech perception measures. In the United Kingdom the current cut-off point to fall within the CI candidacy range is a score of less than 50% on the BKB sentences presented in quiet (presented at 70 dBSPL). GOAL: The specific goal of this article was to review the benefit of adding the AB word test to the assessment test battery for candidacy. RESULTS: The AB word test scores showed good sensitivity and specificity when calculated based on both word and phoneme scores. The word score equivalent for 50% correct on the BKB sentences was 18.5% and it was 34.5% when the phoneme score was calculated; these scores are in line with those used in centres in Wales (15% AB word score). CONCLUSION: The goal of the British Cochlear Implant Group (BCIG) service evaluation was to determine if the pre-implant assessment measures are appropriate and set at the correct level for determining candidacy, the future analyses will determine whether the speech perception cut-off point for candidacy should be adjusted and whether other more challenging measures should be used in the candidacy evaluation.

An evaluation of hearing preservation outcomes in routine cochlear implant care: Implications for candidacy.

INTRODUCTION: A retrospective evaluation of pre- and post-operative audiometric data at a single large UK cochlear implant centre over 25 years was undertaken. METHODS: Analysis of pre-operative hearing levels showed that there was a modest but significant reduction in average pre-operative hearing thresholds among patients referred between 1990 and 2015, particularly in the low frequencies. OUTCOMES: The proportion of those referred who would meet widely-accepted candidacy criteria for electro-acoustic stimulation (EAS) grew significantly over time but in the period 2011-2015 just 9% of those referred had sufficient residual hearing for EAS. On average, implant recipients lost 20 dB hearing at frequencies ≤1000 Hz as a result of the surgery. CONCLUSIONS: The findings suggest that hearing preservation is now widely achievable, and that both candidacy criteria and referrer education should take into account potential EAS benefit.

Perception of the pitch and naturalness of popular music by cochlear implant users.

OBJECTIVES: To assess the perceived pitch and naturalness of popular music by cochlear implant (CI) users. METHODS: Eleven experienced post-lingually deafened adult CI users rated the pitch, naturalness, and clarity of a popular song with 10 frequency allocation settings, including the default. The alternative settings all had logarithmic frequency spacing and frequency shifts of less than one octave compared with the default map. For maps which were perceived as having incorrect pitch, participants adjusted the pitch of the song in real time using a slider, in order to normalize it, and the amount of adjustment was recorded. RESULTS: The default map was rated as having close to correct pitch. Naturalness rating was negatively correlated with basal shift from a baseline logarithmic map, which was the same as the default map for basal electrodes (R(2) = 0.77). Ratings of the clarity of the lyrics were adversely affected by basal shift. The majority of participants were able to rate and adjust pitch appropriately. The frequency shift in the map was highly correlated with participants' adjustments of the pitch slider (R(2) = 0.94), but the adjustments were less than expected for the majority of participants. DISCUSSION: The pitch ratings for the default allocation suggest that participants have acclimatized to their processors' frequency allocations. Adjustment of the pitch of the song was possible for the majority and suggested that all but one participant was experiencing frequency compression. Expansion of the frequency allocation might help to alleviate this. CONCLUSION: Adjustment of the pitch of a popular song could be helpful for tuning CIs.