Reduced alpha amplitudes predict perceptual suppression

Eva Poland,Aishwarya Bhonsle,Melanie Wilke,Iris Steinmann

doi:10.1038/s41598-021-92404-8

Eva Poland, Aishwarya Bhonsle + Show 2 more

Open Access

https://doi.org/10.1038/s41598-021-92404-8

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Abstract

The amplitude of prestimulus alpha oscillations over parieto-occipital cortex has been shown to predict visual detection of masked and threshold-level stimuli. Whether alpha activity similarly predicts target visibility in perceptual suppression paradigms, another type of illusion commonly used to investigate visual awareness, is presently unclear. Here, we examined prestimulus alpha activity in the electroencephalogram (EEG) of healthy participants in the context of a generalized flash suppression (GFS) task during which salient target stimuli are rendered subjectively invisible in a subset of trials following the onset of a full-field motion stimulus. Unlike for masking or threshold paradigms, alpha (8–12 Hz) amplitude prior to motion onset was significantly higher when targets remained subjectively visible compared to trials during which the targets became perceptually suppressed. Furthermore, individual prestimulus alpha amplitudes strongly correlated with the individual trial-to-trial variability quenching following motion stimulus onset, indicating that variability quenching in visual cortex is closely linked to prestimulus alpha activity. We conclude that predictive correlates of conscious perception derived from perceptual suppression paradigms differ substantially from those obtained with “near threshold paradigms”, possibly reflecting the effectiveness of the suppressor stimulus.

Highlights

The amplitude of prestimulus alpha oscillations over parieto-occipital cortex has been shown to predict visual detection of masked and threshold-level stimuli
In the generalized flash suppression (GFS) paradigm that we employ in the current study, a high-contrast target stimulus is shown close to central vision for several hundred milliseconds followed by the onset of a moving surround
We recorded 600 trials from 27 subjects performing a generalized flash suppression (GFS) task[4], a visual illusion by which salient target stimuli can be rendered subjectively invisible after the onset of a random dot motion (RDM) stimulus (Fig. 1A)

Summary

Introduction

The amplitude of prestimulus alpha oscillations over parieto-occipital cortex has been shown to predict visual detection of masked and threshold-level stimuli. While the all-or-none fashion of target disappearance in GFS suggests the contribution of higher-order visual competition and selection processes, the target adaptation requirements underline the importance of pre-surround processes involving topographically organized (i.e. earlier) visual cortices Consistent with this interplay between low- and higher level contributions, neurophysiological experiments that employed GFS or related suppression paradigms have identified neural activity differences between visible and invisible trials in a wide range of brain areas and at different spatial and temporal scales. Higher pre-stimulus alpha power has been linked to visibility in nearthreshold paradigms, with higher alpha power serving as a predictor for impaired target detection and awareness /confidence reports[19,20,21,22,23,24] Building on those near-threshold perceptual studies, we predicted pre-surround alpha power to be higher in trials where targets become invisible (i.e. perceptually suppressed) upon surround onset. Based on these studies we predicted neural variability to be higher in trials where targets become invisible upon surround onset, and individual levels of variability quenching to be lower in subjects that experienced perceptual suppression more frequently

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