Linking Nonlinear Neural Dynamics to Single‐Trial Human Behavior

Cohen, Michael X; Voytek, Bradley

doi:10.1002/9783527671632.ch09

Cited by 9 publications

(12 citation statements)

References 62 publications

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“…Step 1: To test for within‐participant relationships between single‐trial phase and both discrimination accuracy and visual awareness ratings, we employed a measure of circular‐linear association called ‘weighted intertrial phase clustering’ (wITPC) (Cohen & Cavanagh, 2011; Cohen & Voytek, 2013). wITPC represents the resultant vector length (intertrial phase coherence) of single‐trial phase angles, once the length of each individual vector has been weighted by the single‐trial behavioural outcome (i.e., PAS rating or accuracy).…”

Section: Methodsmentioning

confidence: 99%

Low pre‐stimulus EEG alpha power amplifies visual awareness but not visual sensitivity

Benwell

Coldea

Harvey

et al. 2021

Eur J of Neuroscience

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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.

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Section: Methodsmentioning

confidence: 99%

Low pre‐stimulus EEG alpha power amplifies visual awareness but not visual sensitivity

Benwell

Coldea

Harvey

et al. 2021

Eur J of Neuroscience

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“…Because phase is a circular variable, it cannot be related to a linear variable by means of ordinary linear regression. We therefore computed a recently introduce measure of circular-linear association called weighted inter-trial phase clustering (wITPC; Cohen and Cavanagh, 2011;Cohen and Voytek, 2013;Cohen, 2014) to relate prestimulus phase to visibility ratings. wITPC is computed as the resultant vector length, or inter-trial phase clustering, (also called the phase locking factor or inter-trial coherence) of phase angles across trials once the length of each vector has been weighted by the linear variable of interest (an example of this computation with data from one subject is shown in Figure 4B).…”

Section: Methodsmentioning

confidence: 99%

Distinct oscillatory frequencies underlie excitability of human occipital and parietal cortex

Samaha

Gosseries

Postle

2016

Preprint

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Magnetic stimulation (TMS) of human occipital and posterior parietal cortex can give rise to visual sensations called phosphenes, but neural correlates of phosphene perception preceding and succeeding stimulation of both areas are unknown. Using near-threshold TMS with concurrent electroencephalography (EEG) recordings, we uncover oscillatory brain dynamics that covary, on single trials, with the perception of phosphenes following occipital and parietal TMS. Prestimulus power and phase predominantly in the alpha-band (8-13 Hz) predicted occipital TMS phosphenes, whereas higher frequency beta-band (13-20 Hz) power (but not phase) predicted parietal TMS phosphenes. TMS evoked responses related to phosphene perception were similar across stimulation sites and were characterized by an early (200 ms) posterior negativity and a later (>300 ms) parietal positivity in the time domain and an increase in lowfrequency (~5-7 Hz) power followed by a broadband decrease in alpha/beta power in the timefrequency domain. These correlates of phosphene perception closely resemble known electrophysiological correlates of conscious perception using near-threshold visual stimuli and speak to the possible early onset of visual consciousness. The differential pattern of prestimulus predictors of phosphene perception suggest that distinct frequencies reflect cortical excitability within different cortical regions, and that the alpha-band rhythm, long thought of as a general index of cortical inhibition, may not reflect excitability of posterior parietal cortex. Significance statementAlpha-band oscillations are thought to reflect cortical excitability and are therefor suggested to play an important role in gating information transmission across cortex. We directly probe cortical excitability in human occipital and parietal cortex and observed that whereas alpha-band dynamics indeed reflect excitability of occipital areas, beta-band activity was most predictive of parietal cortex excitability. Differences in the state of cortical excitability predicted perceptual outcomes, which were manifest in both early and late patterns of evoked activity, shedding light on the neural correlates of consciousness. Our findings prompt revision of the notion that alpha activity reflects inhibition across all of cortex and suggests instead that excitability in different regions is reflected in distinct frequency bands.

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“…As a control, to ensure that alpha phase was not trivially related to post-stimulus GFP in the C1 time-window, we also analyzed a subset of trials (~33%) which contained only a small change at fixation (FIX trials), but no C1-producing stimuli (see Methods). We computed circular-linear associations using the weighted inter-trial phase coherence (wITPC) 14,29,30 to describe the relationship between single-trial GFP amplitudes (averaged over a 20 ms window centered on the C1 peak for each subject) and oscillatory phase across a range of time and frequency points surrounding stimulus onset (extracted via Morlet wavelet convolution). When normalized with respect to the mean and standard deviation of a permuted wITPC distribution, this metric takes on z units that reflect the strength of phasic coupling between the linear variable (GFP) and circular variable (phase) relative to a null hypothesis distribution (see Methods).…”

Section: Resultsmentioning

confidence: 99%

“…We took two complementary analysis approaches to study the influence of the pre-stimulus phase on GFP amplitudes during the C1 time window. We first compute the weighted intertrial phase coherence (wITPC) 14,29,30 as a means of exploring circular-linear associations between phase and GFP across a range of frequencies and time points. wITPC is computed as the resultant vector length, or inter-trial phase clustering (also called the phase-locking factor or inter-trial coherence), of phase angles across trials once the length of each vector has been weighted by the linear variable of interest (here GFP).…”

Section: Single-trial Circular-linear Association (Witpc)mentioning

confidence: 99%

Pre-Stimulus Alpha-Band Phase Gates Afferent Visual Cortex Responses

Dou

Morrow

Iemi

et al. 2021

Preprint

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The neurogenesis of alpha-band (8-13 Hz) activity has been characterized across many different animal experiments. However, the functional role that alpha oscillations play in perception and behavior has largely been attributed to two contrasting hypotheses, with human evidence in favor of either (or both or neither) remaining sparse. On the one hand, alpha generators have been observed in relay sectors of the visual thalamus and are postulated to phasically inhibit afferent visual input in a feedforward manner 1-4. On the other hand, evidence also suggests that the direction of influence of alpha activity propagates backwards along the visual hierarchy, reflecting a feedback influence upon the visual cortex 5-9. The primary source of human evidence regarding the role of alpha phase in visual processing has been on perceptual reports 10-16, which could be modulated either by feedforward or feedback alpha activity. Thus, although these two hypotheses are not mutually exclusive, human evidence clearly supporting either one is lacking. Here, we present human subjects with large, high-contrast visual stimuli that elicit robust C1 event-related potentials (ERP), which peak between 70-80 milliseconds post-stimulus and are thought to reflect afferent primary visual cortex (V1) input 17-20. We find that the phase of ongoing alpha oscillations modulates the global field power (GFP) of the EEG during this first volley of stimulus processing (the C1 time-window). On the standard assumption 21-23 that this early activity reflects postsynaptic potentials being relayed to visual cortex from the thalamus, our results suggest that alpha phase gates visual responses during the first feed-forward sweep of processing.

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Linking Nonlinear Neural Dynamics to Single‐Trial Human Behavior

Cited by 9 publications

References 62 publications

Low pre‐stimulus EEG alpha power amplifies visual awareness but not visual sensitivity

Low pre‐stimulus EEG alpha power amplifies visual awareness but not visual sensitivity

Distinct oscillatory frequencies underlie excitability of human occipital and parietal cortex

Pre-Stimulus Alpha-Band Phase Gates Afferent Visual Cortex Responses

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