InterlACE Sound Coding for Unilateral and Bilateral Cochlear Implants

Objective: Cochlear implant signal processing strategies define the rules of how acoustic signals are converted into electrical stimulation patterns. Technological and anatomical limitations, however, impose constraints on the signal transmission and the accurate excitation of the auditory nerve. Acoustic signals are degraded throughout cochlear implant processing, and electrical signal interactions at the electrode-neuron interface constrain spectral and temporal precision. In this work, we propose a novel InterlACE signal processing strategy to counteract the occurring limitations. Methods: By replacing the maxima selection of the Advanced Combination Encoder strategy with a method that defines spatially and temporally alternating channels, InterlACE can compensate for discarded signal content of the conventional processing. The strategy can be extended bilaterally by introducing synchronized timing and channel selection. InterlACE was explored unilaterally and bilaterally by assessing speech intelligibility and spectral resolution. Five experienced bilaterally implanted cochlear implant recipients participated in the Oldenburg Sentence Recognition Test in background noise and the spectral ripple discrimination task. Results: The introduced alternating channel selection methodology shows promising outcomes for speech intelligibility but could not indicate better spectral ripple discrimination. Conclusion: InterlACE processing positively affects speech intelligibility, increases available unilateral and bilateral signal content, and may potentially counteract signal interactions at the electrode-neuron interface. Significance: This work shows how cochlear implant channel selection can be modified and extended bilaterally. The clinical impact of the modifications needs to be explored with a larger sample size

Neural Correlates of Binaural Interaction Using Aggregate-System Stimulation in Cochlear Implantees

The importance of binaural cues in auditory stream formation and sound source differentiation is widely accepted. When treating one ear with a cochlear implant (CI) the peripheral auditory system gets partially replaced and processing delays get added potentially, thus important interaural time encoding gets altered. This is a crucial problem because factors like the interaural time delay between the receiving ears are known to be responsible for facilitating such cues, e.g., sound source localization and separation. However, these effects are not fully understood, leaving a lack of systematic binaural fitting strategies with respect to an optimal binaural fusion. To gain new insights into such alterations, we suggest a novel method of free-field evoked auditory brainstem response (ABR) analysis in CI users. As a result, this method does not bypass the technically induced intrinsic delays of the hearing device while leaving the complete electrode array active, thus the most natural way of stimulation is provided and the comparable testing of real world stimuli gets facilitated. Unfortunately, ABRs acquired in CI users are additionally affected by the prominent artifact caused by their electrical stimulation, which severely distorts the desired neural response, thus challenging their analysis. To circumvent this problem, we further introduce a novel narrowband filtering CI artifact removal technique capable of obtaining neural correlates of ABRs in CI users. Consequently, we were able to compare brainstem-level responses collected of 12 CI users and 12 normal hearing listeners using two different stimuli (i.e., chirp and click) at four different intensities each, what comprises an adaption of the prominent brainstem evoked response audiometry serving as an additional evaluation criterion. We analyzed the responses using the average of 2,000 trials in combination with synchronized regularizations across them and found consistent results in their deflections and latencies, as well as in single trial relationships between both groups. This method provides a novel and unique perspective into the natural CI users’ brainstem-level responses and can be practical in future research regarding binaural interaction and fusion. Furthermore, the binaural interaction component (BIC), i.e., the arithmetical difference between the sum of both monaurally evoked ABRs and the binaurally evoked ABR, has been previously shown to be an objective indicator for binaural interaction. This component is unfortunately known to be rather fragile and as a result, a reliable, objective measure of binaural interaction in CI users does not exist to the present date. It is most likely that implantees would benefit from a reliable analysis of brainstem-level and subsequent higher-level binaural interaction, since this could objectively support fitting strategies with respect to a maximization of interaural integration. Therefore, we introduce a novel method capable of obtaining neural correlates of binaural interaction in bimodal CI users by combining recent advances in the field of fast, deconvolution-based ABR acquisitions with the introduced narrowband filtering technique. The proposed method shows a significant improvement in the magnitude of resulting BICs in 10 bimodal CI users and a control-group of 10 normal hearing subjects when compensating the interaural latency difference caused by the technical devices. In total, both proposed studies objectively demonstrate technical-driven interaural latency mismatches. Thus, they strongly emphasize potential benefits when balancing these interaural delays to improve binaural processing by significant increases in associated neural correlates of successful binaural interaction. These results and also the estimated latency differences should be investigated in larger group sizes to further consolidate the results, but confirm the demand for rather binaural solutions than treating hearing losses in an isolated monaural manner.Zusammenfassung Die Notwendigkeit binauraler Verarbeitungsprozesse in der auditorischen Wahrnehmung ist weitestgehend akzeptiert. Bei der Therapie eines Ohres mit einem Cochlea-Implantat (engl. cochlear implant (CI)) wird das periphere auditorische System teilweise ersetzt und verändert, sodass natürliche, interaurale Zeitauflösungen beeinflusst werden. Dieses Problem ist entscheidend, denn Faktoren wie interaurale Laufzeitunterschiede zwischen den aufnehmenden Ohren sind verantwortlich für die Umsetzung der erwähnten binauralen Verarbeitungsprozesse, z.B. Schallquellenlokalisation und -separation. Allerdings sind diese Effekte nicht ausreichend verstanden, weshalb bis heute binaurale Anpassstrategien mit Rücksicht auf eine optimale Fusionierung fehlen. Um neue Einsichten in solche zeitlichen Verzerrungen zu erhalten, schlagen wir ein neues Verfahren der Freifeld evozierten auditorischen Hirnstammpotentiale (engl. auditory brainstem response (ABR)) in CI-Nutzern vor. Diese Methode beinhaltet explizit technisch-induzierte Laufzeiten verwendeter Hörhilfen, sodass eine natürliche Stimulation unter Verwendung von realitätsnahen Stimuli ermöglicht wird. Unglücklicherweise sind ABRs von CI-Nutzern zusätzlich mit Stimulationsartefakten belastet, wodurch benötigte neurale Antworten weiter verzerrt werden und eine entsprechende Analyse der Signale deutlich erschwert wird. Um dieses Problem zu umgehen, schlagen wir eine neue Artefakt- Reduktionstechnik vor, welche auf spektraler Schmalbandfilterung basiert und somit den Erhalt entsprechender, neuraler ABR Korrelate ermöglicht. Diese Methoden erlaubten die Interpretation neuraler Korrelate auf Hirnstammebene unter Verwendung von zwei verschiedenen Stimuli (Chirps und Klicks) unter vier verschiedenen Lautstärken in 12 CI-Nutzern und 12 normalhörenden Probanden. Die beschriebene Prozedur adaptiert somit die weitläufig bekannte Hirnstammaudiometrie (engl. brainstem evoked response audiometry (BERA)), deren Ergebnisse zur zusätzlichen Evaluation des vorgestellten Verfahrens dienten. Die Untersuchung der aus 2000 Einzelantworten erhaltenen Mittelwerte in Kombination mit der Analyse synchronisierter Regularitäten über den Verlauf der Einzelantworten ergab dabei konsistente Beobachtungen in gefundenen Amplituden, Latenzen sowie in Abhängigkeiten zwischen Einzelantworten in beiden Gruppen. Das vorgestellte Verfahren erlaubt somit auf einzigartige Weise neue und ungesehene Einsichten in natürliche, neurale Antworten auf Hirnstammebene von CI-Nutzern, welche in zukünftigen Studien verwendet werden können, um binaurale Interaktionen und Fusionen weiter untersuchen zu können. Interessanterweise hat sich, die auf ABRs basierende, binaurale Interaktionskomponente (engl. binaural interaction component (BIC)) als objektiver Indikator binauraler Integration etabliert. Diese Komponente (d.h. die arithmetische Differenz zwischen der Summe der monauralen Antworten und der binauralen Antwort) ist leider sehr fragil, wodurch ein sicherer und objektiver Nachweis in CI-Nutzern bis heute nicht existiert. Dabei ist es sehr wahrscheinlich, dass gerade Implantatsträger von einer entsprechenden Analyse auf Hirnstammebene und höherrangigen Ebenen deutlich profitieren würden, da dies objektiv Anpassstrategien mit Rücksicht auf eine bestmögliche binaurale Integration ermöglichen könnte. Deshalb stellen wir ein weiteres, neuartiges Verfahren zum Erhalt von neuralen Korrelaten binauraler Interaktion in bimodal versorgten CI-Trägern vor, welches jüngste Erfolge im Bereich der schnellen, entfalltungsbasierten ABR Akquisition und der bereits vorgestellten Schmalband- filterung zur Reduktion von Stimulationsartefakten kombiniert. Basierend auf diesem Verfahren konnten signifikante Verbesserungen in der BIC-Amplitude in 10 bimodal versorgten Patienten sowie 10 normalhörenden Probanden, basierend auf umgesetzte, interaurale Laufzeitkompensationen technischer Hörhilfen, aufgezeigt werden. Insgesamt demonstrieren beide vorgestellten Studien technisch-induzierte, interaurale Laufzeitunterschiede und betonen demnach sehr deutlich potenzielle Vorteile in assoziierten neuralen Korrelaten binauraler Interaktionen, wenn solche Missverhältnisse zeitlich ausgeglichen werden. Die aufgezeigten Ergebnisse sowie die getätigte Abschätzungen technischer Laufzeiten sollte in größeren Gruppen weiter untersucht werden, um die Aussagekraft weiter zu steigern. Dennoch unterstreichen diese Einsichten das Verlangen nach binauralen Lösungsansätzen in der zukünftigen Hörrehabilitation, statt bisheriger isolierter und monauraler Therapien

Neurophysiological study in rat model

학위논문(박사) -- 서울대학교대학원 : 의과대학 의학과, 2022.2. 오승하.With successful experience with unilateral cochlear implants (CIs) for deaf people, bilateral CIs have been used to improve hearing in noise. However, these abilities in bilateral CI users are markedly worse than that of normal-hearing listeners. This is predominantly due to the limited access of CI users to temporal information, which are created by the interaural time difference (ITD). We examined the sensitivity of the neurons in the inferior colliculus (IC) in male and female rats to the ITDs conveyed in electrical pulse trains. Using bipolar pairs of electrodes that selectively activate the auditory nerve fibers at different intracochlear locations, we assessed whether the responses to electrical stimulation with ITDs in different frequency regions were processed differently. Most well-isolated single units responded to the electrical stimulation in only one of the apical or basal cochlear regions, and they were classified as either apical or basal units. Regardless of the cochlear stimulating location, more than 70% of both apical and basal units were sensitive to ITDs of electrical stimulation. However, the pulse rate dependence of neural ITD sensitivity differed significantly depending on the location of the stimulation. Moreover, ITD discrimination thresholds and the relative incidence of ITD tuning type markedly differed between units activated by apical and basal stimulations. With apical stimulation, IC neurons had a higher incidence of peak-type ITD function, which mostly exhibited the steepest position of the tuning curve within the rat’s physiological ITD range of ±160 μs and, accordingly, had better ITD discrimination thresholds than those with basal stimulation. These results support the idea that ITD processing in the IC might be determined by functionally segregated frequency-specific pathways from the cochlea to the auditory midbrain.일측 인공와우이식 수술이 양측 고심도 이상의 청각장애 환자에게서 성공적인 청각재활 방법으로 자리잡았으나, 소음환경에서 제한된 효과를 보이는 경우가 많이 보고되었다. 양측 인공와우이식 수술을 시행한 경우 일측 인공와우에 비해 개선된 효과를 보이기는 하나, 양측 인공와우를 통한 양이청취 효과는 정상 청력 청취자에 비하면 현저하게 떨어지는 것으로 보고된다. 이는 주로 인공와우 청취자에게 양이 시간차 감지 같은 소리의 시간적 정보가 제한적으로 전달되기 때문인 것으로 여겨진다. 본 연구는 양측 인공와우의 한계점을 극복하고자 백서의 청각 중뇌인 하구 신경세포에서 전기적 펄스 열의 양이 시간차 감도를 측정하는 신경생리학적 실험을 진행하였다. 와우 내 위치한 양극성 전극 쌍을 사용하여 상업적인 인공와우 장치보다 더욱 선택적인 전기자극 방식을 활용하였으며, 와우 내 전기자극의 위치 별로 주파수 특이적인 청신경 자극이 가능하게 하였다. 이를 통해 청각 중뇌의 신경세포의 양이 시간차 감도가 와우내 전기자극의 위치에 따라서 어떻게 반응하는지를 연구하였다. 세포외 단일 신경반응 측정 방법을 사용하여 하구 신경세포의 반응을 기록하였으며, 잘 분리된 신경세포는 와우 첨부 쌍극의 자극 또는 와우 기저부 쌍극의 자극 중 하나에만 반응을 보였다. 저주파를 담당하는 와우 첨부의 전기 자극에 반응하는 신경세포들은 첨부 세포 그룹으로 분류하였고, 고주파를 담당하는 와우 기저부의 전기 자극에 반응하는 신경세포들은 기저부 세포 그룹으로 분류하여 반응을 분석하였다. 와우 내 전기자극의 위치에 무관하게 첨부 세포 그룹과 기저부 세포 그룹 모두에서 70%이상의 신경세포들이 전기적 자극의 양이 시간차에 대한 감도를 보였다. 하지만, 전기 자극 빈도에 대한 신경적 양이 시간차 감도의 의존성은 와우 내 전기자극의 위치별로 유의한 차이를 보였다. 또한, 양이 시간차 감지 역치와 양이 시간차 조율 곡선의 형태별 발생 빈도도 첨부 세포 그룹과 기저부 세포 그룹에서 유의한 차이를 보였다. 와우 첨부에 전기적인 자극을 주는 경우, 기저부 자극에 비하여 봉우리 형의 양이 시간차 조율 곡선의 높은 발생 빈도를 보였으며, 대부분의 봉우리 형의 곡선에서는 가장 가파른 곡선 기울기를 보이는 위치가 백서의 생리적인 양이 시간차 감지 범위인 ±160 μs 내에 위치하였다. 그 결과, 첨부 세포 그룹에서 기저부 세포 그룹에 비해 보다 좋은 양이 시간차 감지 역치를 갖는 것으로 나타났다. 본 연구의 결과들은 청각 중뇌인 하구에서 이루어지는 양이 시간차에 대한 처리 과정이 와우로부터 연결되는 주파수 특이 청각로 별로 분리되어 있다는 평행 처리 경로 이론을 뒷받침하고 있으며, 임상적으로도 양측 인공와우의 시간적 양이 효과 개선을 위해서는 저주파수 특이 경로를 보다 선택적으로 자극하는 것이 중요하다는 점을 제시하고 있다.Chapter 1. Introduction 1 1.1. Study Background 1 1.2. Hypothesis of the Study 4 1.3. Research Objectives 5 Chapter 2. Materials and methods 6 2.1. Ethical Approval 6 2.2. Animal Preparation 6 2.3. Surgical Procedures 7 2.4. Electrical Stimulation 10 2.5. Extracellular Single-unit Recording 11 2.6. Frequency Response Area Analysis 14 2.7. Data Aquisition 15 2.8. Data Analysis 16 2.9. Statistical Analysis 22 Chapter 3. Results 26 3.1. FRA Analysis 26 3.2. ITD Sensitivity Analysis 27 3.3. ITD Tuning Curve Analysis 34 Chapter 4. Discussion 38 4.1. Prevalence of the ITDsensitive Units 40 4.2. Pulse Rate Dependence of Neural ITD Sensitivity 42 4.3. Incidence of ITD Tuning Types 45 4.4. Limitations of the Study 49 4.5. Clinical Implications 51 Chapter 5. Conclusions 54 Bibliography 55 Abstract in Korean 81박

Sound Localization in Single-Sided Deaf Participants Provided With a Cochlear Implant

Spatial hearing is crucial in real life but deteriorates in participants with severe sensorineural hearing loss or single-sided deafness. This ability can potentially be improved with a unilateral cochlear implant (CI). The present study investigated measures of sound localization in participants with single-sided deafness provided with a CI. Sound localization was measured separately at eight loudspeaker positions (4°, 30°, 60°, and 90°) on the CI side and on the normal-hearing side. Low- and high-frequency noise bursts were used in the tests to investigate possible differences in the processing of interaural time and level differences. Data were compared to normal-hearing adults aged between 20 and 83. In addition, the benefit of the CI in speech understanding in noise was compared to the localization ability. Fifteen out of 18 participants were able to localize signals on the CI side and on the normal-hearing side, although performance was highly variable across participants. Three participants always pointed to the normal-hearing side, irrespective of the location of the signal. The comparison with control data showed that participants had particular difficulties localizing sounds at frontal locations and on the CI side. In contrast to most previous results, participants were able to localize low-frequency signals, although they localized high-frequency signals more accurately. Speech understanding in noise was better with the CI compared to testing without CI, but only at a position where the CI also improved sound localization. Our data suggest that a CI can, to a large extent, restore localization in participants with single-sided deafness. Difficulties may remain at frontal locations and on the CI side. However, speech understanding in noise improves when wearing the CI. The treatment with a CI in these participants might provide real-world benefits, such as improved orientation in traffic and speech understanding in difficult listening situations

The multi-channel cochlear implant: Multi-disciplinary development of electrical stimulation of the cochlea and the resulting clinical benefit

AbstractThis multi-disciplinary research showed sound could be coded by electrical stimulation of the cochlea and peripheral auditory nervous system. But the temporal coding of frequency as seen in the experimental animal, was inadequate for the important speech frequencies. The data indicated the limitation was due in particular to deterministic firing of neurons and failure to reproduce the normal fine temporo-spatial pattern of neural responses seen with sound. However, the data also showed the need for the place coding of frequency, and this meant multi-electrodes inserted into the cochlea. Nevertheless, before this was evaluated on people we undertook biological safety studies to determine the effects of surgical trauma and electrical stimuli, and how to prevent infection. Then our research demonstrated place of stimulation had timbre and was perceived as vowels. This led to our discovery in 1978 of the formant-extraction speech code that first enabled severely-profoundly deaf people to understand running speech. This result in people who had hearing before becoming severely deaf was an outcome not previously considered possible. In 1985 it was the first multi-channel implant to be approved by the US Food and Drug Administration (FDA). It was also the fore runner of our advanced formant and fixed filter strategies When these codes were used from 1985 for those born deaf or deafened early in life we discovered there was a critical period when brain plasticity would allow speech perception and language to be developed near- normally, and this required in particular the acquisition of place coding. In 1990 this led to the first cochlear implant to be approved by the FDA for use in children. Finally, we achieved binaural hearing in 1989 with bilateral cochlear implants, followed by bimodal speech processing in 1990 with a hearing aid in one ear and implant in the other. The above research has been developed industrially, with for example 250,000 people worldwide receiving the Cochlear device in 2013, and as of December 2012 the NIH estimated that approximately 324,200 people worldwide had received this and other implants (NIH Publication No. 11-4798).This article is part of a Special Issue entitled <Lasker Award>

Binaural summation, binaural unmasking and fluctuating masker benefit in bimodal and bilateral adult cochlear implant users

OBJECTIVES : The number of bilateral adult cochlear implant (CI) users and bimodal CI users is expanding worldwide. The addition of a hearing aid (HA) in the contralateral non-implanted ear (bimodal) or a second CI (bilateral) can provide CI users with some of the benefits associated with listening with two ears. Our was to examine whether bilateral and bimodal CI users demonstrate binaural summation, binaural unmasking and a fluctuating masker benefit. METHODS : Direct audio input was used to present stimuli to 10 bilateral and 10 bimodal CochlearTM CI users. Speech recognition in noise (speech reception threshold, SRT) was assessed monaurally, diotically (identical signals in both devices) and dichotically (antiphasic speech) with different masking noises (steady-state and interrupted), using the digits-in-noise test. RESULTS : Bilateral CI users demonstrated a trend towards better SRTs with both CIs than with one CI. Bimodal CI users showed no difference between the bimodal SRT and the SRT for CI alone. No significant differences in SRT were found between the diotic and dichotic conditions for either group. Analyses of electrodograms created from bilateral stimuli demonstrated that substantial parts of the interaural speech cues were preserved in the Advanced Combination Encoder, an n-of-m channel selection speech coding strategy, used by the CI users. Speech recognition in noise was significantly better with interrupted noise than with steady-state masking noise for both bilateral and bimodal CI users. CONCLUSION : Bilateral CI users demonstrated a trend towards binaural summation, but bimodal CI users did not. No binaural unmasking was demonstrated for either group of CI users. A large fluctuating masker benefit was found in both bilateral and bimodal CI users.https://www.tandfonline.com/loi/ycii20hj2022Speech-Language Pathology and Audiolog

Multifaceted evaluation of a binaural cochlear‐ implant sound‐processing strategy inspired by the medial olivocochlear reflex

[ES]El objetivo de esta tesis es evaluar experimentalmente la audición de los usuarios de implantes cocleares con una estrategia de procesamiento binaural de sonidos inspirada en el reflejo olivococlear medial, denominada "estrategia MOC". La tesis describe cuatro estudios dirigidos a comparar la inteligibilidad del habla en ruido, la localización de fuentes sonoras y el esfuerzo auditivo con procesadores de sonido estándar y con diversos procesadores MOC diseñados para reflejar de forma más o menos realista el tiempo de activación del reflejo olivococlear medial natural y sus efectos sobre la comprensión coclear humana