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Neural processing around 200 ms after stimulus-onset correlates with subjective visual awareness
Mika Koivisto1, Simone Grassini1
1Department of Psychology, University of Turku, Finland; Centre for Cognitive Neuroscience, University of Turku, Finland; Turku Brain and Mind Centre, University of Turku, Finland.
Neuropsychologia
|March 6, 2016
Summary
Subjective visual awareness is linked to early brain activity in the visual cortex, specifically the enhanced N200 component. This finding supports theories where early neural processing generates conscious visual experiences.
Area of Science:
- Neuroscience
- Cognitive Science
- Psychology
Background:
- Understanding the neural basis of visual awareness is crucial for cognitive neuroscience.
- Debate exists on whether awareness correlates with early sensory processing or later cognitive integration.
Purpose of the Study:
- To investigate whether visual awareness is associated with early visual cortex activity or widespread neural activation.
- To identify event-related potential (ERP) correlates of subjective visual awareness.
Main Methods:
- Participants performed forced-choice localization and rated subjective awareness of liminal visual targets.
- Electroencephalography (EEG) was used to measure neural activity.
- Event-related potentials (ERPs) were analyzed, controlling for response accuracy to isolate awareness effects.
Main Results:
- High-awareness trials showed an enhanced contralateral N200 (180-280 ms) compared to low-awareness trials, termed visual awareness negativity (VAN).
- The VAN effect correlated with sensitivity (d'), suggesting it reflects graded awareness.
- Later P3 amplitudes (after 350 ms) correlated with response bias, not awareness itself.
Conclusions:
- Early enhanced N200 activity correlates with graded visual awareness.
- Findings support theories where early visual cortex activity underlies subjective visual experiences.
- Distinguishes neural correlates of awareness from response biases.
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