Abstract
Electrophysiological recordings are commonly used to study the neural correlates of consciousness in humans. Previous research is inconsistent as to whether awareness can be indexed with visual awareness negativity (VAN) at about 200 ms or if it occurs later. The present study was preregistered with two main aims: First, to provide independent evidence for or against the presence of VAN, and second, to study whether stimulus size may account for the inconsistent findings. Subjects were shown low-contrast Gaussian filtered gratings (Gabor patches) in the four visual quadrants. Gabor size (large and small) was varied in different sessions and calibrated to each subject’s threshold of visual awareness. Event-related potentials were derived from trials in which subjects localized the Gabors correctly to capture the difference between trials in which they reported awareness versus no awareness. Bayesian analyses revealed very strong evidence for the presence of VAN for both Gabor sizes. However, there was no evidence for or against an effect of stimulus size. The present findings provide evidence for VAN as an early neural correlate of awareness.
Highlights
Electrophysiological recordings are commonly used to study the neural correlates of consciousness in humans
Research on visual evoked potentials derived from electroencephalography (EEG) has suggested two potential neural correlates of visual awareness: visual awareness negativity (VAN) and late positivity (LP; for a review, see Koivisto & Revonsuo, 2010)
In between-subjects analyses, Bayesian independent-samples t tests were used to determine if VAN and LP differed between Gabor sizes for subjects that completed either session
Summary
All subjects had normal or corrected-to-normal vision and were recruited from local universities and through online billboards They were compensated with either movie vouchers or course credits after their participation in two sessions (large Gabor and small Gabor). When the preregistered exclusion criteria were adopted, several subjects were excluded from one of the sessions: Subjects did not correctly localize 70% of the control trials (n = 1 for large Gabors and n = 7 for small Gabors). Subjects did not show any clear N200 in the control trials (n = 4 for large Gabors and n = 6 for small Gabors). Subjects were excluded if they had fewer than five critical trials per quadrant (n = 7 for large Gabors and n = 13 for small Gabors), as explained below. Together with the event markers from the presentation computer, these signals were recorded as TTL triggers with a Cedrus StimTracker (Cedrus Corporation, San Pedro, CA)
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