Oscillatory processes in multistable perception

In den vergangenen Jahren wurden eine Reihe spezifischer oszillatorischer EEG-Komponenten beschrieben, welche im Zuge einer Wahrnehmungsreversion während des Betrachtens eines multistabilen visuellen Reizes auftreten. Die für die vorliegende Arbeit relevanten Komponenten sind: (a) eine langsame positive Welle im Delta Band (0-4 Hz), welche ihr Maximum etwa 250 ms nach einer Wahrnehmungsreversion (angezeigt durch einen Knopfdruck der Probanden) erreicht, und als Abschluss des Reversionsprozesses bzw. als die Etablierung einer neuen stabilen Wahrnehmung interpretiert wurde; (b) eine Abnahme der Aktivität im Alpha Band (8-12 Hz), welche etwa 1000 ms vor einer Wahrnehmungsreversion beginnt und als Destabilisierung des aktuellen Perzepts interpretiert wurde. Da das Auftreten eines Wahrnehmungswechsels in den bisherigen Studien jedoch über einen Knopfdruck der Probanden rückgemeldet wurde, ist unklar in welchem Ausmaß elektrophysiologische Korrelate der motorischen Aktivität die beschriebenen perzeptuellen Komponenten beeinflussen oder überlagern. In der vorliegenden Arbeit wurden die reversionsgebundenen EEG-Komponenten im Delta- und Alpha Band unabhängig von motorischer Aktivität untersucht, indem Wahrnehmungsreversion und rückmeldender Knopfdruck durch ein spezielles experimentelles Design getrennt wurden. Die Ergebnisse zeigen klar, dass die zuvor beschriebenen oszillatorischen Komponenten im Delta- und Alpha Band während einer Wahrnehmungsreversion auch in Abwesenheit einer motorischen Antwort auftreten. Sie können daher als Teil jenes neuronalen Mechanismus gesehen werden, durch dessen Hilfe das Gehirn mehrdeutige visuelle Reize disambiguiert und verarbeitet.Previous work from our research group has shown a number of distinct oscillatory EEG responses occurring during the observation of multistable patterns. These are in particular: (a) a slow positive wave in the delta band (0-4 Hz), peaking about 250 ms before a button press indicating a perceptual reversal, which was interpreted as the completion of the reversal process and/or the establishment of a new stable percept; (b) a decrease in alpha band power (8-12 Hz) starting at 1000 ms before perceptual reversals, interpreted as the destabilization of the current percept. However, as subjects had to press a button in order to indicate reversals, a possible overlap with motor-related potentials could not be ruled out. The present study investigated reversal-related delta and alpha band components independently from motor activity, by separating the button press from the reversal through a special experimental setup. The results clearly show that the delta- and alpha band modulations do occur during a multistable pattern change even in absence of a motor response. Thus, following previous interpretations, they may be seen as part of the oscillatory mechanisms by which the brain disambiguates and processes visual input

Taking a Call Is Facilitated by the Multisensory Processing of Smartphone Vibrations, Sounds, and Flashes

Many electronic devices that we use in our daily lives provide inputs that need to be processed and integrated by our senses. For instance, ringing, vibrating, and flashing indicate incoming calls and messages in smartphones. Whether the presentation of multiple smartphone stimuli simultaneously provides an advantage over the processing of the same stimuli presented in isolation has not yet been investigated. In this behavioral study we examined multisensory processing between visual (V), tactile (T), and auditory (A) stimuli produced by a smartphone. Unisensory V, T, and A stimuli as well as VA, AT, VT, and trisensory VAT stimuli were presented in random order. Participants responded to any stimulus appearance by touching the smartphone screen using the stimulated hand (Experiment 1), or the non-stimulated hand (Experiment 2). We examined violations of the race model to test whether shorter response times to multisensory stimuli exceed probability summations of unisensory stimuli. Significant violations of the race model, indicative of multisensory processing, were found for VA stimuli in both experiments and for VT stimuli in Experiment 1. Across participants, the strength of this effect was not associated with prior learning experience and daily use of smartphones. This indicates that this integration effect, similar to what has been previously reported for the integration of semantically meaningless stimuli, could involve bottom-up driven multisensory processes. Our study demonstrates for the first time that multisensory processing of smartphone stimuli facilitates taking a call. Thus, research on multisensory integration should be taken into consideration when designing electronic devices such as smartphones

Generalization of auditory expertise in audio engineers and instrumental musicians

From auditory perception to general cognition, the ability to play a musical instrument has been associated with skills both related and unrelated to music. However, it is unclear if these effects are bound to the specific characteristics of musical instrument training, as little attention has been paid to other populations such as audio engineers and designers whose auditory expertise may match or surpass that of musicians in specific auditory tasks or more naturalistic acoustic scenarios. We explored this possibility by comparing students of audio engineering (n = 20) to matched conservatory-trained instrumentalists (n = 24) and to naive controls (n = 20) on measures of auditory discrimination, auditory scene analysis, and speech in noise perception. We found that audio engineers and performing musicians had generally lower psychophysical thresholds than controls, with pitch perception showing the largest effect size. Compared to controls, audio engineers could better memorise and recall auditory scenes composed of non-musical sounds, whereas instrumental musicians performed best in a sustained selective attention task with two competing streams of tones. Finally, in a diotic speech-in-babble task, musicians showed lower signal-to-noise-ratio thresholds than both controls and engineers; however, a follow-up online study did not replicate this musician advantage. We also observed differences in personality that might account for group-based self-selection biases. Overall, we showed that investigating a wider range of forms of auditory expertise can help us corroborate (or challenge) the specificity of the advantages previously associated with musical instrument training

Functional significance of EEG beta-band oscillations in multisensory perception and selective attention

Oszillationen sind ein allgegenwärtiges Phänomen neuronaler Aktivität. Der Beta Band Frequenzbereich (13-30 Hz, BBA) wurde ursprünglich vor allem mit motorischen und somatosensorischen Prozessen assoziiert. Erst jüngst schreibt man diesem auch komplexe Funktionen in selektiver Aufmerksamkeit und neuronaler Integration zu. Die vorliegende Arbeit hat mittels Elektroenzephalographie die Rolle von BBA bei einer Reihe höherer kognitiver Aufgaben untersucht. Studie 1 hat sich mit dem Einfluss visueller Reize auf die Verarbeitung von Schmerzreizen beschäftigt. Es zeigt sich, dass BBA in sensomotorischen Arealen das Ausmaß an Integration zwischen visuellen Reizen und Schmerzreizen widerspiegelt. Die Stärke der Integration ist dabei invers proportional zur Stärke der Schmerzreize. Studie 2 hat die Lokalisation und Diskrimination von Sprache bei Personen mit beidseitigem Cochlear Implantat untersucht. Diese haben Schwierigkeiten bei der Lokalisation von Sprache, was auf eine vorhergehende Degeneration von auditorischen Pfaden zurückzuführen sein könnte. Die Studie zeigt eine stärkere Modulation medio-zentraler BBA während Sprachlokalisation, was einen Zusammenhang zwischen BBA und Verarbeitungsaufwand und selektiver räumlicher Aufmerksamkeit nahelegt. In Studie 3 wurde das Verhältnis zwischen intersensorischer Aufmerksamkeit und zeitlicher Orientierung untersucht. Es zeigt sich sich dass die Modulation antizipatorischer BBA unabhängig voneinander sowohl intersensorische Aufmerksamkeit als auch zeitliche Orientierung reflektiert. Die vorliegende Arbeit erweitert somit bisherige Forschungsergebnisse, indem sie die Beteiligung von BBA während multisensorischer Verarbeitung, selektiver Aufmerksamkeit, sowie intersensorischer Aufmerksamkeit und zeitlicher Orientierung zeigt. Zugleich unterstreicht sie die Bedeutung zukünftiger Forschung, die zu einem tieferen Verständnis der Rolle von BBA bei sensomotorischen Prozessen, Aufmerksamkeit und kortikaler Integration führen wird.Oscillations are a ubiquitous phenomenon in neural activity. The beta-band frequency range (BBA, 13-30 Hz) has traditionally been associated with sensorimotor behaviour. Only recently, research has become aware of its putative role in selective attention and large-scale neural communication. The present thesis investigated the functional significance of BBA in a broad range of cognitive tasks, using electroencephalography (EEG). Study 1 examined the influence of simultaneous visual input on the processing of pain, which is known to engage a widely distributed cortical network. The study showed that sensorimotor BBA reflects the strengths of multisensory processing between visual and pain stimuli. In Study 2, auditory speech localization and discrimination was examined in patients with bilateral cochlear implants. This group of individuals is known to have difficulties in speech localization, which might derive from a prior degeneration of auditory pathways. The study demonstrates an increased medio-central BBA suppression during speech localization in cochlear implant users, suggesting that BBA reflects selective spatial attention to auditory speech stimuli. Study 3 investigated the processes of intersensory attention and temporal orienting in a multisensory cue-target paradigm. The study showed that modulations of anticipatory BBA reflect intersensory attention as well as temporal orienting. Interestingly the results did not reveal interactions between the two mechanisms, suggesting that intersensory attention and temporal orienting can operate independent of each other. Taken together, this thesis extends previous research by demonstrating the crucial role of BBA in multisensory processing, selective attention and intersensory attention as well as temporal orienting. The studies also emphasize the relevance of future research in this field, which will further uncover the significance of BBA in sensorimotor, attentional, and integrative functions

Multiple items in working memory are cyclically activated at a theta-rhythm

Representations held in working memory (WM) are crucial in guiding human attention in a goal-directed fashion. Currently, it is debated whether only a single or several of these representations can be active and bias behaviour at any given moment. In our present study, 25 university students performed a behavioural dense-sampling experiment to produce an estimate of the temporal activation patterns of two simultaneously held visual templates. We report two key novel results. First, the performance related to both representations was not continuous, but fluctuated rhythmically at 6 Hz. This corresponds to neural oscillations in the theta-band, whose functional importance in WM is well established. Second, our findings suggest that two concurrently held representations may be prioritized in alternation, not simultaneously. Our data extend recent research on rhythmic sampling of external information by demonstrating an analogous mechanism in the cyclic activation of internal WM representations

Cyclic reactivation of internal working memory representations of distinct feature dimensions

Recently, several behavioral studies have demonstrated 4-10 Hz rhythmic fluctuations in attention. So far, this attentional sampling has only been demonstrated with regards to external stimuli. Attention, however, is often directed towards internal working memory representations. We conducted a human behavioral dense-sampling experiment on whether simultaneously held representations of two distinct feature dimensions (color and orientation) also exhibit a rhythmic temporal profile. We found an oscillatory component at 9.4 Hz in the joint time-courses of both representations, presumably reflecting a common early perceptual sampling process in the alpha-frequency range. Further, we observed an oscillatory component at 3.5 Hz with a significant phase-difference between feature dimensions. This likely corresponds to a later attentional sampling process, indicating that internal representations of distinct features are activated in alteration. In summary, we demonstrate the cyclic reactivation of internal representations, as well as the co-occurrence of perceptual- and attentional rhythmic fluctuations at distinct frequencies

Dissociation of reversal- and motor-related delta- and alpha-band responses during visual multistable perception

Multistable visual perception refers to phenomena, in which one invariant stimulus pattern is perceived in at least two different, mutually exclusive ways. In this EEG study we differentiate between perceptual- and motor-related processes during perceptual reversals. Delta- and alpha-band activity was analyzed while participants answered to a perceptual reversal either immediately or with a delay of approximately 1500 ms, thereby separating reversal-related and motor-related activity. On the single sweep level a reversal-related positive delta response and reversal-related desynchronisation of alpha activity could be detected irrespective of the motor response. Both conditions elicited the strongest reversal-related modulations at posterior locations. Contrary, motor-related responses were found predominantly at central locations. These findings were supported by a control experiment, using a slightly modified stimulus that allowed unambiguous perceptual changes to be triggered exogenously. In conclusion, this study demonstrates that the brain response to perceptual reversals differs from motor-related processes elicited by the button press indicating the perceptual reversal. The results of this study, therefore, indicate that perceptual- and motor-related processes are achieved in multiple selectively distributed and parallel working oscillatory networks of the brain

Entrainment Project

EEG Data for sharin