303 research outputs found

    Alpha-band rhythms in visual task performance: phase-locking by rhythmic sensory stimulation

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    Oscillations are an important aspect of neuronal activity. Interestingly, oscillatory patterns are also observed in behaviour, such as in visual performance measures after the presentation of a brief sensory event in the visual or another modality. These oscillations in visual performance cycle at the typical frequencies of brain rhythms, suggesting that perception may be closely linked to brain oscillations. We here investigated this link for a prominent rhythm of the visual system (the alpha-rhythm, 8-12 Hz) by applying rhythmic visual stimulation at alpha-frequency (10.6 Hz), known to lead to a resonance response in visual areas, and testing its effects on subsequent visual target discrimination. Our data show that rhythmic visual stimulation at 10.6 Hz: 1) has specific behavioral consequences, relative to stimulation at control frequencies (3.9 Hz, 7.1 Hz, 14.2 Hz), and 2) leads to alpha-band oscillations in visual performance measures, that 3) correlate in precise frequency across individuals with resting alpha-rhythms recorded over parieto-occipital areas. The most parsimonious explanation for these three findings is entrainment (phase-locking) of ongoing perceptually relevant alpha-band brain oscillations by rhythmic sensory events. These findings are in line with occipital alpha-oscillations underlying periodicity in visual performance, and suggest that rhythmic stimulation at frequencies of intrinsic brain-rhythms can be used to reveal influences of these rhythms on task performance to study their functional roles

    Not a slave to the rhythm: the perceptual consequences of rhythmic visual stimulation

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    We investigated whether rhythmic visual stimulation leads to changes in visual perception attributable to the entrainment of endogenous alpha-band oscillations. First, we report evidence that the attentional blink phenomenon is not selectively modified by alpha-band rhythmic entrainment. Next, we provide evidence that changes in single target identification following rhythmic stimulation are poorly explained by rhythmic entrainment, but well explained by alternative factors. We report failures to replicate the results of two previous visual entrainment studies supporting the hypothesis that alpha-band rhythmic stimulation leads to matching rhythmic fluctuations in target detection. Finally, we examined whether temporal acuity during an RSVP sequence is dependent on rhythmic entrainment by studying the role of object change on temporal acuity, finding novel results inconsistent with the predictions of the rhythmic entrainment model. We conclude that visual perception is robust against entrainment to task-irrelevant rhythmic visual inputs and that endogenous and externally driven oscillations in the visual system may be functionally distinct

    Binding Mechanisms in Visual Perception and Their Link With Neural Oscillations: A Review of Evidence From tACS

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    Neurophysiological studies in humans employing magneto- (MEG) and electro- (EEG) encephalography increasingly suggest that oscillatory rhythmic activity of the brain may be a core mechanism for binding sensory information across space, time, and object features to generate a unified perceptual representation. To distinguish whether oscillatory activity is causally related to binding processes or whether, on the contrary, it is a mere epiphenomenon, one possibility is to employ neuromodulatory techniques such as transcranial alternating current stimulation (tACS). tACS has seen a rising interest due to its ability to modulate brain oscillations in a frequency-dependent manner. In the present review, we critically summarize current tACS evidence for a causal role of oscillatory activity in spatial, temporal, and feature binding in the context of visual perception. For temporal binding, the emerging picture supports a causal link with the power and the frequency of occipital alpha rhythms (8–12 Hz); however, there is no consistent evidence on the causal role of the phase of occipital tACS. For feature binding, the only study available showed a modulation by occipital alpha tACS. The majority of studies that successfully modulated oscillatory activity and behavioral performance in spatial binding targeted parietal areas, with the main rhythms causally linked being the theta (~7 Hz) and beta (~18 Hz) frequency bands. On the other hand, spatio-temporal binding has been directly modulated by parieto-occipital gamma (~40–60 Hz) and alpha (10 Hz) tACS, suggesting a potential role of cross-frequency coupling when binding across space and time. Nonetheless, negative or partial results have also been observed, suggesting methodological limitations that should be addressed in future research. Overall, the emerging picture seems to support a causal role of brain oscillations in binding processes and, consequently, a certain degree of plasticity for shaping binding mechanisms in visual perception, which, if proved to have long lasting effects, can find applications in different clinical populations

    Do somatosensory oscillations relate to tactile attention? Extracting the phase of transcranial Alternating Current Stimulation (tACS) during stimulus presentation.

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    Attentional mechanisms allow for the prioritization of information depending on the task at hand. Evidence from Electroencephalography (EEG) suggests that lateralised changes in the amplitude of alpha oscillations (8-­‐14 Hz) are linked to orienting attention and that the phase of an oscillatory cycle can affect how behavioral and perceptual information is processed. Transcranial alternating current stimulation (tACS) is a non-­‐invasive brain stimulation method that involves the application of weak electric currents to the scalp. tACS provides the ability to entrain intrinsic oscillations to specific frequencies. Through the employment of new hardware, the timings of stimuli presentation and the phase of tACS signals were accurately recorded so that their timings could be compared. This setup was implemented in an ongoing study that utilised participant individualized alpha and beta (25 Hz) stimulation during two tactile attention tasks. Results indicated that during alpha stimulation, performance in an endogenous tactile attention was mediated by the phase of the tACS signal, with a distribution of reaction times (RTs) that approximately followed the pattern of the waveform signal. The phase of the tACS signal during beta stimulation was shown to mediate performance during an exogenous tactile attention task. Both these results indicate that the fastest and slowest RTs occur at opposite phase positions of the tACS signal, providing novel evidence for a phasic relationship between performance variability and somatosensory attention
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