Anja Hahne

Users of hearing aids (HAs) and cochlear implants (CIs) experience significant difficulty understanding a target speaker in multi-talker environments or when other background noise is present. Segregation of a particular voice from background noise occurs partly through enhanced cortical tracking of amplitude fluctuations in the target signal. Measuring a person's cortical tracking allows decoding their focus of attention and may be used for neurofeedback in hearing devices, potentially aiding their users with speech-in-noise comprehension. Most studies on cortical tracking have employed typical hearing (TH) individuals, whereas studies in people with hearing impairment whose cortical tracking may differ are still scarce. The objective of this study was to compare cortical speech tracking of HA (n=29) and CI users (n=24) to that of age-matched TH individuals (n=29). We recorded EEG data while the participants attended one of two competing talkers (one with a female and one with a male voice), in a free-field acoustic environment. Importantly, HA users as well as CI users used their personal, clinically-fitted devices. Cortical speech tracking was assessed through linear backward and forward models that related the EEG data to the speech envelope. For the CI users, electrical artifacts stemming from the implant were addressed through a bespoke method for artifact rejection. We found that the HA group exhibited cortical tracking and attentional modulation that were largely comparable to those of the TH group. CI users also showed successful cortical tracking. However, they displayed a profound deficit in attentional modulation, seen in the significantly poorer neural segregation of the attended vs. the ignored speech streams. These results shed light on a neurobiological mechanism for speech-in-noise comprehension and have implications for neurofeedback in hearing devices.

Objective. Understanding speech in the presence of background noise such as other speech streams is a difficult problem for people with hearing impairment, and in particular for users of cochlear implants (CIs). To improve their listening experience, auditory attention decoding (AAD) aims to decode the target speaker of a listener from electroencephalography (EEG), and then use this information to steer an auditory prosthesis towards this speech signal. In normal-hearing individuals, deep neural networks (DNNs) have been shown to improve AAD compared to simpler linear models. We aim to demonstrate that DNNs can improve attention decoding in CI users too, which would make them the state-of-the-art candidate for a neuro-steered CI. Approach. To this end, we first collected an EEG dataset on selective auditory attention from 25 bilateral CI users, and then implemented both a linear model as well as a convolutional neural network (CNN) for attention decoding. Moreover, we introduced a novel, objective CI-artifact removal strategy and evaluated its impact on decoding accuracy, alongside learnable speaker classification using a support vector machine (SVM). Main results. The CNN outperformed the linear model across all decision window sizes from 1 to 60 s. Removing CI artifacts modestly improved the CNN’s decoding accuracy. With SVM classification, the CNN decoder reached a peak mean decoding accuracy of 74% at the population level for a 60 s decision window. Significance. These results demonstrate the superior potential of CNN-based decoding for neuro-steered CIs, which could improve speech perception of its users in cocktail party situations significantly.

Zusammenfassung: Sprachliche Verarbeitungsprozesse können objektiv gemessen werden, z.B. mithilfe später Komponenten im evozierten Hirnpotenzial. Die etablierteste Komponente in diesem Forschungsbereich ist die N400-Komponente, eine Negativierung mit einem Peak bei frühestens 400ms nach Stimulusbeginn und einem zentro-parietalen Maximum. Sie spiegelt semantische Verarbeitungsprozesse wider. Ihr Vorhandensein sowie ihre zeitliche und quantitative Ausprägung lassen Rückschlüsse auf die Güte der Sprachverarbeitung zu. Somit ist sie geeignet, das Sprachverstehen von besonderen Populationsgruppen zu erfassen, z.B. um den Fortschritt im Sprachverstehen bei Nutzern von Cochlea-Implantaten (CI) zu messen. Im Folgenden wird ein Überblick über die Verwendung der N400-Komponente im Bereich der CI-Forschung gegeben. Es werden Studien mit erwachsenen CI-Nutzern vorgestellt, bei denen die N400 die Qualität des Sprachverstehens mit der elektrischen Stimulation abbildet. Darüber hinaus werden Studien mit CI-versorgten Kindern besprochen, bei denen das Auftreten der N400-Komponente den Erwerb des Wortschatzes reflektiert.

Viele Cochlea-Implantat-Patienten berichten über Einschränkungen in der Musikwahrnehmung, wobei jedoch selten die unterschiedlichen musikalischen Dimensionen berücksichtigt werden. In dieser Studie wurden 3 Aspekte der Musikverarbeitung untersucht: musikalische Diskriminationsfähigkeit (DF), Zugang zu musikalischer Bedeutungsinformation und subjektiver Musikgenuss. CI-Träger mit unterschiedlicher Hörgeschichte sowie Kontrollprobanden nahmen an der Studie teil. Die DF wurden mithilfe eines standardisierten Tests überprüft. Evozierte Potentiale wurden auf visuell präsentierte Wörter abgeleitet, die im Anschluss an akustisch komplexe Musikstücke präsentiert wurden. Das Wort war entweder eine semantisch passende Assoziation zum Musikstück oder nicht. Der Musikgenuss wurde mittels Fragebögen erhoben. Die DF waren bei allen CI-Gruppen im Vergleich zur Kontrollgruppe deutlich eingeschränkt. Bei den evozierten Potentiale zeigten jedoch postlinguale CI-Träger (poCIT) sowie junge Erwachsene, die als Kind früh mit einem CI versorgt worden waren, einen Effekt analog zu Normalhörenden. Den Musikgenuss beurteilten poCIT allerdings deutlich schlechter als prälinguale CI-Träger (präCIT). Trotz der eingeschränkten DF waren poCIT und früh versorgte präCIT in der Lage, die assoziativ vermittelte Bedeutung der Musik zu aktivieren, was den spät versorgten präCIT und den einseitig ertaubten Probanden nicht gelang. Einen den normalhörenden vergleichbaren Musikgenuss wiesen wiederum nur die beiden präCIT-Gruppen auf. Die klare Dissoziation dieser musikalischen Ebenen zeigt, dass Rückschlüsse zur Musikverarbeitung bei CI-Trägern sehr differenziert beurteilt werden müssen und sowohl die betrachtete musikalische Dimension als auch die Hörgeschichte der Probanden Berücksichtigung finden sollten. Publication Date: 10 June 2020 (online) © . © Georg Thieme Verlag KG Stuttgart · New York

Language is a fundamental part of human cognition. The question of whether language is processed independently of speech, however, is still heavily discussed. The absence of speech in deaf signers offers the opportunity to disentangle language from speech in the human brain. Using probabilistic tractography, we compared brain structural connectivity of adult deaf signers who had learned sign language early in life to that of matched hearing controls. Quantitative comparison of the connectivity profiles revealed that the core language tracts did not differ between signers and controls, confirming that language is independent of speech. In contrast, pathways involved in the production and perception of speech displayed lower connectivity in deaf signers compared to hearing controls. These differences were located in tracts towards the left pre-supplementary motor area and the thalamus when seeding in Broca’s area, and in ipsilateral parietal areas and the precuneus with seeds in left posterior temporal regions. Furthermore, the interhemispheric connectivity between the auditory cortices was lower in the deaf than in the hearing group, underlining the importance of the transcallosal connection for early auditory processes. The present results provide evidence for a functional segregation of the neural pathways for language and speech.

In the present study we explore the implications of acquiring language when relying mainly or exclusively on input from a cochlear implant (CI), a device providing auditory input to otherwise deaf individuals. We focus on the time course of semantic learning in children within the second year of implant use; a period that equals the auditory age of normal hearing children during which vocabulary emerges and extends dramatically. 32 young bilaterally implanted children saw pictures paired with either matching or non-matching auditory words. Their electroencephalographic responses were recorded after 12, 18 and 24 months of implant use, revealing a large dichotomy: Some children failed to show semantic processing throughout their second year of CI use, which fell in line with their poor language outcomes. The majority of children, though, demonstrated semantic processing in form of the so-called N400 effect already after 12 months of implant use, even when their language experience relied exclusively on the implant. This is slightly earlier than observed for normal hearing children of the same auditory age, suggesting that more mature cognitive faculties at the beginning of language acquisition lead to faster semantic learning.

Objective: Measurement of electrophysiological correlates of discrimination abilities of basic musical features in pre- and postlingually deafened adult cochlear implant (CI) users. Study Design: Electroencephalographic study. Comparison between CI users and matched normal hearing controls. Patients: Thirty-six hearing impaired adults using a cochlear implant for 4 to 15 months. Profound hearing impairment was acquired either before (N = 12) or after language acquisition (N = 17). Seven patients suffered from a single-sided deafness. Methods: Presentation of auditory stimuli consisting of musical four tone standard patterns and deviant patterns varying with regard to tone pitch, timbre, intensity, and rhythm of two different degrees. Analysis of electrophysiological, event-related mismatch responses. Results: Cochlear implant users elicited significant mismatch responses on most deviant features. Comparison to controls revealed significantly smaller mismatch negativity amplitudes. Except for one parameter (pitch) there were no reliable differences between pre- and postlingually deafened CI users. Conclusion: Despite a highly reduced complexity of neural auditory stimulation by the cochlear implant device in comparison to the physiological cochlear input, CI users exhibit cortical discriminatory responses to relatively subtle basic tonal alterations.

Direct stimulation of the auditory nerve via a Cochlear Implant (CI) enables profoundly hearing-impaired people to perceive sounds. Many CI users find language comprehension satisfactory, but music perception is generally considered difficult. However, music contains different dimensions which might be accessible in different ways. We aimed to highlight three main dimensions of music processing in CI users which rely on different processing mechanisms: (1) musical discrimination abilities, (2) access to meaning in music and (3) subjective music appreciation. All three dimensions were investigated in two CI user groups (post- and prelingually deafened CI users, all implanted as adults) and a matched normal hearing control group. The meaning of music was studied by using event-related potentials (with the N400 component as marker) during a music-word priming task while music appreciation was gathered by a questionnaire. The results reveal a double dissociation between the three dimensions of music processing. Despite impaired discrimination abilities of both CI user groups compared to the control group, appreciation was reduced only in postlingual CI users. While musical meaning processing was restorable in postlingual CI users, as shown by a N400 effect, data of prelingual CI users lack the N400 effect and indicate previous dysfunctional concept building.

In most everyday situations sensorimotor processes are quite complex because situations often require to carry out several actions in a specific temporal order; i.e. one has to cascade different actions. While it is known that changes to stimuli affect action cascading mechanisms, it is unknown whether action cascading changes when sensory stimuli are not manipulated, but the neural architecture to process these stimuli is altered. In the current study we test this hypothesis using prelingually deaf subjects as a model to answer this question. We use a system neurophysiological approach using event-related potentials (ERPs) and source localization techniques. We show that prelingually deaf subjects show improvements in action cascading. However, this improvement is most likely not due to changes at the perceptual (P1-ERP) and attentional processing level (N1-ERP), but due to changes at the response selection level (P3-ERP). It seems that the temporo-parietal junction (TPJ) is important for these effects to occur, because the TPJ comprises overlapping networks important for the processing of sensory information and the selection of responses. Sensory deprivation thus affects cognitive processes downstream of sensory processing and only these seem to be important for behavioral improvements in situations requiring complex sensorimotor processes and action cascading.