Abstract
A fundamental unsettled dispute concerns how fast the brain generates subjective visual experiences. Both early visual cortical activation and later activity in fronto-parietal global neuronal workspace correlate with conscious vision, but resolving which of the correlates causally triggers conscious vision has proved a methodological impasse. We show that participants can report whether or not they consciously perceived a stimulus in just over 200 ms. These fast consciousness reports were extremely reliable, and did not include reflexive, unconscious responses. The neural events that causally generate conscious vision must have occurred before these behavioral reports. Analyses on single-trial neural correlates of consciousness revealed that the late cortical processing in fronto-parietal global neuronal workspace (∼300 ms) started after the fastest consciousness reports, ruling out the possibility that this late activity directly reflects the emergence of visual consciousness. The consciousness reports were preceded by a negative amplitude difference (∼160–220 ms) that spread from occipital to frontal cortex, suggesting that this correlate underlies the emergence of conscious vision.
Highlights
Understanding the neuronal mechanisms that enable humans to consciously experience visual or any other sensory information is one of the fundamental questions of cognitive neuroscience
Analyses on single-trial neural correlates of consciousness revealed that the late cortical processing in fronto-parietal global neuronal workspace ($300 ms) started after the fastest consciousness reports, ruling out the possibility that this late activity directly reflects the emergence of visual consciousness
The consciousness reports were preceded by a negative amplitude difference ($160–220 ms) that spread from occipital to frontal cortex, suggesting that this correlate underlies the emergence of conscious vision
Summary
Understanding the neuronal mechanisms that enable humans to consciously experience visual or any other sensory information is one of the fundamental questions of cognitive neuroscience. Conscious vision correlates with early activation in visual cortex and with later widespread activation in fronto-parietal cortices (Lamme, 2010; Dehaene and Changeux, 2011). According to the early vision model (Lamme, 2010; Railo, Koivisto and Revonsuo, 2011), early recurrent communication of neural populations within the visual cortex enables subjective conscious perception, whereas the fronto-parietal networks are activated as conscious information is processed further and accessed by the cognitive system. The global neural workspace model (Gaillard et al, 2009; Dehaene and Changeux, 2011; Dehaene, 2014) posits that the early activation in visual cortex is preconscious, and can only enter consciousness if it accesses coordinated communication in the fronto-parietal global workspace.
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