Distinct cortical codes and temporal dynamics for conscious and unconscious percepts

Conscious perception of a stimulus is linked to a specific sequence of brain processes that unfold after about 270 milliseconds, involving superior parietal and superior frontal regions. Using EEG and MEG recordings during a task where participants reported the location and visibility of a brief visual target, multivariate pattern analysis showed that information about stimulus location is still processed in the cortex even when the stimulus is not consciously seen (blindsight). However, only consciously perceived stimuli trigger additional, time-limited neural activity in higher-order brain areas, whereas unconscious processing decays slowly without this chain of activity.

Study at a glance

Abstract

The neural correlates of consciousness are typically sought by comparing the overall brain responses to perceived and unperceived stimuli. However, this comparison may be contaminated by non-specific attention, alerting, performance, and reporting confounds. Here, we pursue a novel approach, tracking the neuronal coding of consciously and unconsciously perceived contents while keeping behavior identical (blindsight). EEG and MEG were recorded while participants reported the spatial location and visibility of a briefly presented target. Multivariate pattern analysis demonstrated that considerable information about spatial location traverses the cortex on blindsight trials, but that starting ≈270 ms post-onset, information unique to consciously perceived stimuli, emerges in superior parietal and superior frontal regions. Conscious access appears characterized by the entry of the perceived stimulus into a series of additional brain processes, each restricted in time, while the failure of conscious access results in the breaking of this chain and a subsequent slow decay of the lingering unconscious activity.