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Kevin Ortego, Michael Pitts, Michael Cohen; Neural correlates of visual awareness and task-relevance in a no-report masking paradigm. Journal of Vision 2020;20(11):1600. doi: https://doi.org/10.1167/jov.20.11.1600.
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What are the neural signatures associated with perceptual awareness? The P3b event-related potential (ERP) has been widely claimed to differentiate between visible and invisible stimuli. For example, Dehaene et al. (2001) observed widespread neural activation and a P3b only in response to visible stimuli. However, it is unclear if this activation is associated with perceptual awareness or post-perceptual processes (e.g., memory encoding, decision-making, motor planning, etc.). To examine this possibility, we used a visual masking paradigm to manipulate awareness (i.e., visible vs. invisible) and task-relevance (i.e., report what you saw vs. do not report what you saw). Here, the target stimuli were line drawings of animals and objects that appeared for 33ms. In the masked condition, 100ms masks immediately preceded and followed the stimuli, while in the visible condition, the masks were separated from the stimuli by 200ms blank periods. During task-relevant blocks, subjects reported whether they saw an animal, object, or nothing. In the task-irrelevant blocks, subjects made no responses to the animals and objects. Instead, they counted how many times a green circle appeared and provided their answer after each block. Critically, the stimuli were identical between the two conditions. The only thing that changed was the task being performed. In the task-relevant condition we found a robust P3b wave (300-600ms), replicating previous results. In the task-irrelevant condition, however, no such wave was observed (Bayes factor=0.001). ERP decoding analyses, in which we trained classifiers on the task-relevant condition and tested them on the task-irrelevant condition, revealed that only early (<300ms) neural dynamics generalized across conditions. We replicated the P3b and decoding results in a second experiment in which stimuli were always visible (unmasked). Overall, this pattern of results suggests that the P3b is related to task performance, while earlier ERPs may be more closely linked with visual awareness.
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