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EEG data in 3 different flavors

Voluntary allocation of visual attention is controlled by top-down signals generated within the Frontal Eye Fields able to change the excitability of visual areas. However, the mechanism through which this control is achieved remains elusive. Here, we emulated the generation of an attentional signal using single-pulse transcranial magnetic stimulation to activate the Frontal Eye Fields and tracked its consequences over the visual cortex. First, we documented electrophysiological changes of this activation using electroencephalography and found evidence for a phase-reset of oscillatory activity over remote occipital sites at beta frequency. We then probed for perceptual consequences of this top-down triggered phase-reset and found that Frontal Eye Field-activation generates cyclic modulation of visual motion discrimination ability and extrastriate but not primary visual cortex excitability, again at beta frequency. We conclude that top-down signals originating in Frontal Eye Fields causally shape perception by modulating visual cortex activity through mechanisms of oscillatory phase-realignment.

Alpha-band oscillatory activity over occipito-parietal areas is involved in shaping perceptual and cognitive processes, with a growing body of electroencephalographic (EEG) evidence indicating that pre-stimulus alpha-band amplitude relates to the subjective perceptual experience, but not to objective measures of visual task performance (discrimination accuracy). The primary aim of the present transcranial magnetic stimulation (TMS) study was to investigate whether causality can be established for this relationship, using rhythmic (alpha-band) TMS entrainment protocols. It was anticipated that pre-stimulus 10 Hz-TMS would induce changes in subjective awareness ratings but not accuracy, in the visual hemifield contralateral to TMS. To test this, we administered 10 Hz-TMS over the right intraparietal sulcus prior to visual stimulus presentation in 17 participants, while measuring their objective performance and subjective awareness in a visual discrimination task. Arrhythmic and 10 Hz sham-TMS served as control conditions (within-participant design). Resting EEG was used to record individual alpha frequency (IAF). A study conducted in parallel to ours with a similar design but reported after we completed data collection informed further, secondary analyses for a causal relationship between pre-stimulus alpha-frequency and discrimination accuracy. This was explored through a regression analysis between rhythmic-TMS alpha-pace relative to IAF and performance measures. Our results revealed that contrary to our primary expectation, pre-stimulus 10 Hz-TMS did not affect subjective measures of performance, nor accuracy, relative to control-TMS. This null result is in accord with a recent finding showing that for influencing subjective measures of performance, alpha-TMS needs to be applied post-stimulus. In addition, our secondary analysis showed that IAF was positively correlated with task accuracy across participants, and that 10 Hz-TMS effects on accuracy—but not awareness ratings—depended on IAF: The slower (or faster) the IAF, relative to the fixed 10 Hz TMS frequency, the stronger the TMS-induced performance improvement (or worsening), indicating that 10 Hz-TMS produced a gain (or a loss) in individual performance, directly depending on TMS-pace relative to IAF. In support of recent reports, this is evidence for alpha-frequency playing a causal role in perceptual sensitivity likely through regulating the speed of sensory sampling.

Pre‐stimulus oscillatory neural activity has been linked to the level of awareness of sensory stimuli. More specifically, the power of low frequency oscillations (primarily in the alpha‐band, i.e. 8‐14 Hz) prior to stimulus‐onset is inversely related to measures of subjective performance in visual tasks, such as confidence and visual awareness. Intriguingly, the same EEG‐signature does not seem to influence objective measures of task performance (i.e. accuracy). We here examined whether this dissociation holds when stringent accuracy measures are used. Previous EEG‐studies have employed 2‐alternative forced‐choice (2‐AFC) discrimination tasks to link pre‐stimulus oscillatory activity to correct/incorrect responses as an index of accuracy/objective performance at the single‐trial level. However, 2‐AFC tasks do not provide a good estimate of single‐trial accuracy, as many of the responses classified as correct will be contaminated by guesses (with the chance correct response rate being 50%). Here instead, we employed a 19‐AFC letter identification task to measure accuracy and the subjectively reported level of perceptual awareness on each trial. As the correct guess rate is negligible (~5%), this task provides a purer measure of accuracy. Our results replicate the inverse relationship between pre‐stimulus alpha/beta‐band power and perceptual awareness ratings in the absence of a link to discrimination accuracy. Pre‐stimulus oscillatory phase did not predict either subjective awareness or accuracy. Our results hence confirm a dissociation of the pre‐stimulus EEG power ‐ task performance link for subjective versus objective measures of performance, and further substantiate pre‐stimulus alpha power as a neural predictor of visual awareness.