Activity in the lateral occipital cortex between 200 and 300 ms distinguishes between physically identical seen and unseen stimuli.
Frontiers in Human Neuroscience January 1, 2012 Ying Liu, Anne-Lise Paradis, Lydia Yahia-Cherif et al.
Neural activity over posterior brain regions between 200 and 300 milliseconds after a stimulus distinguishes seen from unseen stimuli. Using magnetoencephalography (MEG) in 14 participants who viewed faint colored gratings at the threshold of visibility, the main sources of awareness-related activity were localized bilaterally in the lateral occipital complex and right posterior infero-temporal region, not in frontal or parietal areas. Color congruency with a preceding cue did not improve detection of the grating, and awareness-related activity was independent of color congruency. However, color congruency was processed differently when a grating was present versus absent, engaging left parietal regions. The findings suggest an occipital source of visual awareness insensitive to color congruency and a separate parietal process sensitive to co-localized features but not directly involved in awareness.