In Search of Consciousness: Examining the Temporal Dynamics of Conscious Visual Perception using MEG time-series data

Brain activity carries information about visual stimuli even when people are not consciously aware of them, but conscious awareness is associated with stronger neural representations. Using magneto-encephalography and multivariate pattern analysis, the authors decoded stimulus information from brain recordings while participants viewed stimuli at threshold contrast in a backward masking paradigm. Consciousness was measured with both forced-choice categorization and self-report. Stimulus information was present in brain activity during both conscious and non-conscious trials, but it was enhanced in conscious trials. The enhancement of neural activity characterizing visual consciousness arises as early as 180 milliseconds after stimulus onset.

Study at a glance

Abstract

Abstract The mere presence of information in the brain does not always mean that this information is available to consciousness (de-Wit, Alexander, Ekroll, & Wagemans, 2016). Experiments using paradigms such as binocular rivalry, visual masking, and the attentional blink have shown that visual information can be processed and represented by the visual system without reaching consciousness. Using multivariate pattern analysis (MVPA) and magneto-encephalography (MEG), we investigated the temporal dynamics of information processing for unconscious and conscious stimuli. We decoded stimulus information from the brain recordings while manipulating visual consciousness by presenting stimuli at threshold contrast in a backward masking paradigm. Participants’ consciousness was measured using both a forced-choice categorisation task and self-report. We show that brain activity during both conscious and non-conscious trials contained stimulus information, and that this information was enhanced in conscious trials. Overall, our results indicate that visual consciousness is characterised by enhanced neural activity representing the visual stimulus, and that this effect arises as early as 180 ms post-stimulus onset.