Multiple independent components contribute to event-related potential correlates of conscious vision
Research has revealed two major event-related potential (ERP) markers of visual awareness: the earlier Visual Awareness Negativity (VAN, around 150-250 ms after stimulus onset), and the following Late Positivity (LP, around 300-500 ms after stimulus onset). Understanding the neural sources that give rise to VAN and LP is important in order to understand what kind of neural processes enable conscious visual perception. Although the ERPs afford high temporal resolution, their spatial resolution is limited because multiple separate sources sum up at the scalp level. In the present study, we sought to characterize the locations and time-courses of independent neural sources underlying the ERP correlates of visual awareness by means of Independent Component Analysis (ICA). ICA allows identifying and localizing the temporal dynamics of different neural sources that contribute to the ERP correlates of conscious perception. The present results show that while LP reflects a combination of multiple sources distributed among frontal, parietal and occipito-temporal cortex, the sources of VAN are localized to posterior areas including occipital and temporal cortex. In addition, our analysis reveals that activity in very early sources (roughly -100-100 ms after stimulus onset) in temporal and fronto-parietal cortices correlates with conscious vision.