Correction: Music listening while you learn: No influence of background music on verbal learning

BACKGROUND: Whether listening to background music enhances verbal learning performance is still disputed. In this study we investigated the influence of listening to background music on verbal learning performance and the associated brain activations. METHODS: Musical excerpts were composed for this study to ensure that they were unknown to the subjects and designed to vary in tempo (fast vs. slow) and consonance (in-tune vs. out-of-tune). Noise was used as control stimulus. 75 subjects were randomly assigned to one of five groups and learned the presented verbal material (non-words with and without semantic connotation) with and without background music. Each group was exposed to one of five different background stimuli (in-tune fast, in-tune slow, out-of-tune fast, out-of-tune slow, and noise). As dependent variable, the number of learned words was used. In addition, event-related desynchronization (ERD) and event-related synchronization (ERS) of the EEG alpha-band were calculated as a measure for cortical activation. RESULTS: We did not find any substantial and consistent influence of background music on verbal learning. There was neither an enhancement nor a decrease in verbal learning performance during the background stimulation conditions. We found however a stronger event-related desynchronization around 800 - 1200 ms after word presentation for the group exposed to in-tune fast music while they learned the verbal material. There was also a stronger event-related synchronization for the group exposed to out-of-tune fast music around 1600 - 2000 ms after word presentation. CONCLUSION: Verbal learning during the exposure to different background music varying in tempo and consonance did not influence learning of verbal material. There was neither an enhancing nor a detrimental effect on verbal learning performance. The EEG data suggest that the different acoustic background conditions evoke different cortical activations. The reason for these different cortical activations is unclear. The most plausible reason is that when background music draws more attention verbal learning performance is kept constant by the recruitment of compensatory mechanisms

Evaluation of evoked potentials to dyadic tones after cochlear implantation

Auditory evoked potentials are tools widely used to assess auditory cortex functions in clinical context. However, in cochlear implant users, electrophysiological measures are challenging due to implant-created artefacts in the EEG. Here, we used independent component analysis to reduce cochlear implant-related artefacts in event-related EEGs of cochlear implant users (n = 12), which allowed detailed spatio-temporal evaluation of auditory evoked potentials by means of dipole source analysis. The present study examined hemispheric asymmetries of auditory evoked potentials to musical sounds in cochlear implant users to evaluate the effect of this type of implantation on neuronal activity. In particular, implant users were presented with two dyadic tonal intervals in an active oddball design and in a passive listening condition. Principally, the results show that independent component analysis is an efficient approach that enables the study of neurophysiological mechanisms of restored auditory function in cochlear implant users. Moreover, our data indicate altered hemispheric asymmetries for dyadic tone processing in implant users compared with listeners with normal hearing (n = 12). We conclude that the evaluation of auditory evoked potentials are of major relevance to understanding auditory cortex function after cochlear implantation and could be of substantial clinical value by indicating the maturation/reorganization of the auditory system after implantatio

Visual activation of auditory cortex reflects maladaptive plasticity in cochlear implant users

Cross-modal reorganization in the auditory cortex has been reported in deaf individuals. However, it is not well understood whether this compensatory reorganization induced by auditory deprivation recedes once the sensation of hearing is partially restored through a cochlear implant. The current study used electroencephalography source localization to examine cross-modal reorganization in the auditory cortex of post-lingually deafened cochlear implant users. We analysed visual-evoked potentials to parametrically modulated reversing chequerboard images between cochlear implant users (n = 11) and normal-hearing listeners (n = 11). The results revealed smaller P100 amplitudes and reduced visual cortex activation in cochlear implant users compared with normal-hearing listeners. At the P100 latency, cochlear implant users also showed activation in the right auditory cortex, which was inversely related to speech recognition ability with the cochlear implant. These results confirm a visual take-over in the auditory cortex of cochlear implant users. Incomplete reversal of this deafness-induced cortical reorganization might limit clinical benefit from a cochlear implant and help explain the high inter-subject variability in auditory speech comprehensio

Brain responses to musical feature changes in adolescent cochlear implant users

Cochlear implants (CIs) are primarily designed to assist deaf individuals in perception of speech, although possibilities for music fruition have also been documented. Previous studies have indicated the existence of neural correlates of residual music skills in postlingually deaf adults and children. However, little is known about the behavioral and neural correlates of music perception in the new generation of prelingually deaf adolescents who grew up with CIs. With electroencephalography (EEG), we recorded the mismatch negativity (MMN) of the auditory event-related potential to changes in musical features in adolescent CI users and in normal-hearing (NH) age mates. EEG recordings and behavioral testing were carried out before (T1) and after (T2) a 2-week music training program for the CI users and in two sessions equally separated in time for NH controls. We found significant MMNs in adolescent CI users for deviations in timbre, intensity, and rhythm, indicating residual neural prerequisites for musical feature processing. By contrast, only one of the two pitch deviants elicited an MMN in CI users. This pitch discrimination deficit was supported by behavioral measures, in which CI users scored significantly below the NH level. Overall, MMN amplitudes were significantly smaller in CI users than in NH controls, suggesting poorer music discrimination ability. Despite compliance from the CI participants, we found no effect of the music training, likely resulting from the brevity of the program. This is the first study showing significant brain responses to musical feature changes in prelingually deaf adolescent CI users and their associations with behavioral measures, implying neural predispositions for at least some aspects of music processing. Future studies should test any beneficial effects of a longer lasting music intervention in adolescent CI users.Peer reviewe

Transcranial direct current stimulation of the prefrontal cortex modulates working memory performance: combined behavioural and electrophysiological evidence

The present study demonstrates that tDCS can alter WM performance by modulating the underlying neural oscillations. This result can be considered an important step towards a better understanding of the mechanisms involved in tDCS-induced modulations of WM performance, which is of particular importance, given the proposal to use electrical brain stimulation for the therapeutic treatment of memory deficits in clinical settings

Neurophysiological evidence of cortical reorganisation and impaired musical sound perception in cochlear-implant users

Hearing can be restored in individuals suffering from severe and profound hearing loss by means of a cochlear implant (CI). This sophisticated bionic device aims at mimicking the natural input into the human auditory system . However, the human brain has to learn to use the coarse, artificial input provided by a CI, thereby showing a remarkable amount of plasticity. The primary aim of the present empirical work is to better understand this adaptation process in CI users, in particular regarding musical input. The two studies reported in this thesis evaluated electrophysiological correlates of musical sound perception in CI users. However, in CI users electrophysiological measures are challenging because any acoustic stimulation in implantees generates an electrical artefact that inevitably corrupts the signal of the Electroencephalogram (EEG). Here we used independent component analysis (ICA) to reduce CI-related artefacts in event-related EEGs, which allowed the detailed spatio-temporal evaluation of auditory evoked potentials (AEPs) in CI users. In the first experiment an active oddball paradigm was used which required the participants to discriminate between different musical sounds. This study focused on hemispheric asymmetry during musical sound processing in CI users (n = 12) and matched normal-hearing (NH) controls (n = 12) in order to better understand functional changes after cochlear implantation in the auditory cortex contra- and ipsilateral to the implanted device. In the second experiment, musical sound discrimination ability was systematically examined in CI users (n = 12) and NH listeners (n = 12) by behavioural discrimination tasks and mismatch negativity (MMN) recordings. Auditory discrimination profiles were obtained by using a set of clarinet sounds varying along different acoustic dimensions (frequency / intensity / duration) and deviation magnitudes (four levels). On the methodic level, the results from the two studies demonstrate that CI-related artefacts in EEGs of CI users can be successfully reduced by means of ICA. We show that successful artefact reduction allows for evaluating neurophysiological mechanisms of restored auditory function in CI users . On the functional level, the results revealed smaller N1/MMN amplitudes and altered hemispheric asymmetries in CI users compared to NH listeners, indicating that CI users show experience-related changes in the auditory cortex contra- and ipsilateral to the CI device. Furthermore, the second study revealed reduced musical sound discrimination ability in different acoustic dimensions in CI users when compared to NH listeners. These results agree with previous findings of poor music perception with CI and thereby emphasize that degraded acoustic signals of CIs do not provide sufficient information for satisfactory music and tone perception. On the other hand, the results from the two studies suggest that in addition to limitations in the implant signal, music processing with CI may be influenced by demographic factors as well, such as duration of profound deafness and CI-auditory experience. We conclude that a multi-dimensional approach including technical improvements as well as the development of individual behavioural training protocols seems to be necessary to achieve the long-term goal of qualitatively improved music perception with CIs. Bei Personen mit schwerem und vollständigem Hörverlust kann die Hörfähigkeit durch ein Cochlea-Implantat (CI) wiederhergestellt werden. Dieses hochentwickelte biotechnische Gerät hat das Ziel den natürlichen Input in das menschliche auditorische System zu imitieren. Das menschliche Gehirn muss jedoch die Bedeutung des imitierten und daher vergleichsweise undifferenzierten Inputs des CIs erlernen, was ein bemerkenswertes Ausmass an Plastizität erfordert. Das primäre Ziel der vorliegenden Arbeit ist diesen Adaptations-Prozess bei CI-Trägern besser zu verstehen, insbesondere bei musikalischem Input. Die zwei Studien dieser Arbeit untersuchten die elektrophysiologischen Korrelate von musikalischer Klang-Wahrnehmung mit einem CI. Bei CI-Trägern sind elektrophysiologische Messungen stark eingeschränkt, weil jede akustische Stimulation bei Implantat-Trägern ein elektrisches Artefakt im Elektroencephalogramm (EEG) erzeugt. Deshalb haben wir in den zwei Studien die Independent Component Analysis (ICA) angewandt um CI-generierte Artefakte in evozierten Potentialen von CI-Trägern zu reduzieren, was auch bei CI-Trägern eine detaillierte räumlich-zeitliche Analyse von auditorisch-evozierten Potentialen (AEPs) ermöglichte. Im ersten Experiment wurde eine aktive Oddball-Aufgabe gestellt, bei welcher die Versuchspersonen verschiedene musikalische Klänge unterscheiden mussten. Diese Studie fokussierte auf die Hemisphären-Asymmetrie während der musikalischen Klang-Verarbeitung bei CI-Trägern (n = 12) und normalhörenden Kontrollpersonen (n = 12), um die CI-induzierten funktionellen Veränderungen im auditorischen Kortex kontra- und ipsilateral zum implantierten Gerät besser zu verstehen. Im zweiten Experiment wurde die Fähigkeit zur Ton-Diskrimination bei CI-Trägern (n = 12) und Normalhörenden (n =12) systematisch mit Verhaltenstests und Messungen der Mismatch-Negativity (MMN) untersucht. Dabei wurden Klarinetten-Töne präsentiert, welche sich in verschiedenen akustischen Dimensionen (Frequenz / Intensität / Dauer) und im Ausmass der Abweichung (4 Stufen) unterschieden. Auf der methodischen Ebene zeigen die Studien, dass die neurophysiologischen Mechanismen von wiederhergestellten auditorischen Funktionen bei CI-Trägern mit ICA erfolgreich untersucht werden können, indem ICA tatsächlich die CI-Artefakte im EEG von CI-Trägern reduziert. Auf der funktionellen Ebene zeigen die Ergebnisse kleinere N1/MMN-Amplitude n und veränderte Hemisphären-Asymmetrien bei CI-Trägern im Vergleich zu Normalhörenden, was auf erfahrungsbezogene Veränderungen im auditorischen Kortex von CI-Trägern kontra- und ipsilateral zum implantierten Gerät hindeutet. Die zweite Studie weist ausserdem reduzierte Leistungen der Ton-Diskriminationsfähigkeit in verschiedenen akustischen Dimensionen bei CI-Trägern im Vergleich zu Normalhörenden aus. Diese Ergebnisse stimmen mit früheren Erkenntnissen, wonach mit CI bloss eine verminderte Musik-Wahrnehmung gegeben ist, überein, das heisst, die reduzierte Komplexität des CI-Signals lässt keine zufriedenstellende Ton- und Musik-Wahrnehmung zu. Andererseits zeigen die Resultate der beiden Studien, dass neben dem limitieren CI-Signal auch demographische Faktoren wie z.B. die Dauer der Taubheit oder die CI-Tragzeit einen Einfluss auf die Musik-Verarbeitung bei CI-Trägern haben können. Daraus folgern wir, dass das langfristige Ziel einer qualitativ verbesserten Musik-Wahrnehmung mit CI nur durch einen multi-dimensionalen Ansatz zu erreichen ist, welcher neben technischen Verbesserungen auch die Entwicklung von individuellen Verhaltens-Trainings einbezieht

Consequences of Stimulus Type on Higher-Order Processing in Single-Sided Deaf Cochlear Implant Users

Single-sided deaf subjects with a cochlear implant (CI) provide the unique opportunity to compare central auditory processing of the electrical input (CI ear) and the acoustic input (normal-hearing, NH, ear) within the same individual. In these individuals, sensory processing differs between their two ears, while cognitive abilities are the same irrespectively of the sensory input. To better understand perceptualcognitive factors modulating speech intelligibility with a CI, this electroencephalography study examined the centralauditory processing of words, the cognitive abilities, and the speech intelligibility in 10 postlingually single-sided deaf CI users. We found lower hit rates and prolonged response times for word classification during an oddball task for the CI ear when compared with the NH ear. Also, event-related potentials reflecting sensory (N1) and higher-order processing (N2/N4) were prolonged for word classification (targets versus nontargets) with the CI ear compared with the NH ear. Our results suggest that speech processing via the CI ear and the NH ear differs both at sensory (N1) and cognitive (N2/N4) processing stages, thereby affecting the behavioral performance for speech discrimination. These results provide objective evidence for cognition to be a key factor for speech perception under adverse listening conditions, such as the degraded speech signal provided from the CI. (C) 2016 S. Karger AG, Base

On the relationship between auditory cognition and speech intelligibility in cochlear implant users: An ERP study

There is a high degree of variability in speech intelligibility outcomes across cochlear-implant (CI) users. To better understand how auditory cognition affects speech intelligibility with the CI, we performed an electroencephalography study in which we examined the relationship between central auditory processing, cognitive abilities, and speech intelligibility. Postlingually deafened CI users (N=13) and matched normal-hearing (NH) listeners (N=13) performed an oddball task with words presented in different background conditions (quiet, stationary noise, modulated noise). Participants had to categorize words as living (targets) or non-living entities (standards). We also assessed participants' working memory (WM) capacity and verbal abilities. For the oddball task, we found lower hit rates and prolonged response times in CI users when compared with NH listeners. Noise-related prolongation of the N1 amplitude was found for all participants. Further, we observed group-specific modulation effects of event-related potentials (ERPs) as a function of background noise. While NH listeners showed stronger noise-related modulation of the N1 latency, CI users revealed enhanced modulation effects of the N2/N4 latency. In general, higher-order processing (N2/N4, P3) was prolonged in CI users in all background conditions when compared with NH listeners. Longer N2/N4 latency in CI users suggests that these individuals have difficulties to map acoustic-phonetic features to lexical representations. These difficulties seem to be increased for speech-in-noise conditions when compared with speech in quiet background. Correlation analyses showed that shorter ERP latencies were related to enhanced speech intelligibility (N1, N2/N4), better lexical fluency (N1), and lower ratings of listening effort (N2/N4) in CI users. In sum, our findings suggest that CI users and NH listeners differ with regards to both the sensory and the higher-order processing of speech in quiet as well as in noisy background conditions. Our results also revealed that verbal abilities are related to speech processing and speech intelligibility in CI users, confirming the view that auditory cognition plays an important role for CI outcome. We conclude that differences in auditory-cognitive processing contribute to the variability in speech performance outcomes observed in CI users

Visuo-tactile interactions in the congenitally deaf: A behavioral and event-related potential study

Auditory deprivation is known to be accompanied by alterations in visual processing. Yet not much is known about tactile processing and the interplay of the intact sensory modalities in the deaf. We presented visual, tactile, and visuo-tactile stimuli to congenitally deaf and hearing individuals in a speeded detection task. Analyses of multisensory responses showed a redundant signals effect that was attributable to a coactivation mechanism in both groups, although the redundancy gain was less in the deaf. In line with these behavioral results, on a neural level, there were multisensory interactions in both groups that were again weaker in the deaf. In hearing but not deaf participants, somatosensory event-related potential N200 latencies were modulated by simultaneous visual stimulation. A comparison of unisensory responses between groups revealed larger N200 amplitudes for visual and shorter N200 latencies for tactile stimuli in the deaf. Furthermore, P300 amplitudes were also larger in the deaf. This group difference was significant for tactile and approached significance for visual targets. The differences in visual and tactile processing between deaf and hearing participants, however, were not reflected in behavior. Both the behavioral and electroencephalography (EEG) results suggest more pronounced multisensory interaction in hearing than in deaf individuals. Visuo-tactile enhancements could not be explained by perceptual deficiency, but could be partly attributable to inverse effectiveness

Cross-Modal Functional Reorganization of Visual and Auditory Cortex in Adult Cochlear Implant Users Identified with fNIRS

Cochlear implant (CI) users show higher auditory-evoked activations in visual cortex and higher visual-evoked activation in auditory cortex compared to normal hearing (NH) controls, reflecting functional reorganization of both visual and auditory modalities. Visual-evoked activation in auditory cortex is a maladaptive functional reorganization whereas auditory-evoked activation in visual cortex is beneficial for speech recognition in CI users. We investigated their joint influence on CI users’ speech recognition, by testing 20 postlingually deafened CI users and 20 NH controls with functional near-infrared spectroscopy (fNIRS). Optodes were placed over occipital and temporal areas to measure visual and auditory responses when presenting visual checkerboard and auditory word stimuli. Higher cross-modal activations were confirmed in both auditory and visual cortex for CI users compared to NH controls, demonstrating that functional reorganization of both auditory and visual cortex can be identified with fNIRS. Additionally, the combined reorganization of auditory and visual cortex was found to be associated with speech recognition performance. Speech performance was good as long as the beneficial auditory-evoked activation in visual cortex was higher than the visual-evoked activation in the auditory cortex. These results indicate the importance of considering cross-modal activations in both visual and auditory cortex for potential clinical outcome estimation