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

Benwell, C. S.Y., Coldea, A., Harvey, M. and Thut, G. (2022) Low pre-stimulus EEG alpha power amplifies visual awareness but not visual sensitivity. European Journal of Neuroscience, 55(11-12), pp. 3125-3140. (doi: 10.1111/ejn.15166) (PMID:33655566)

Abstract

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.

• Item Type: Articles
• Status: Published
• Refereed: Yes
• Glasgow Author(s) Enlighten ID: Benwell, Mr Christopher and Coldea, Andra and Thut, Professor Gregor and Harvey, Professor Monika
• Authors: Benwell, C. S.Y., Coldea, A., Harvey, M., and Thut, G.
• College/School: College of Medical Veterinary and Life Sciences > School of Psychology & Neuroscience
• Journal Name: European Journal of Neuroscience
• Publisher: Wiley
• ISSN: 0953-816X
• ISSN (Online): 1460-9568
• Published Online: 02 March 2021
• Copyright Holders: Copyright © 2021 The Authors
• First Published: First published in European Journal of Neuroscience 55(11-12): 3125-3140
• Publisher Policy: Reproduced under a Creative Commons license

Project Code	Award No	Project Name	Principal Investigator	Funder's Name	Funder Ref	Lead Dept
167201		Natural and modulated neural communication: State-dependent decoding and driving of human Brain Oscillations	Gregor Thut	Wellcome Trust (WELLCOTR)	098434/Z/12/Z	NP - Centre for Cognitive Neuroimaging (CCNi)