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The Journal of Neuroscience, March 4, 2009, 29(9):2725-2732; doi:10.1523/JNEUROSCI.3963-08.2009

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Behavioral/Systems/Cognitive
To See or Not to See: Prestimulus Phase Predicts Visual Awareness

Kyle E. Mathewson,^1,2 Gabriele Gratton,^1,2 Monica Fabiani,^1,2 Diane M. Beck,^1,2 and Tony Ro³

¹Department of Psychology and ²Beckman Institute, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, and ³Program in Cognitive Neuroscience and Department of Psychology, The City College of the City University of New York, New York, New York 10031

Correspondence should be addressed to Tony Ro at the above address. Email: tro{at}ccny.cuny.edu

We often fail to see something that at other times is readily detectable. Because the visual stimulus itself is unchanged, this variability in conscious awareness is likely related to changes in the brain. Here we show that the phase of EEG rhythm measured over posterior brain regions can reliably predict both subsequent visual detection and stimulus-elicited cortical activation levels in a metacontrast masking paradigm. When a visual target presentation coincides with the trough of an wave, cortical activation is suppressed as early as 100 ms after stimulus onset, and observers are less likely to detect the target. Thus, during one cycle lasting 100 ms, the human brain goes through a rapid oscillation in excitability, which directly influences the probability that an environmental stimulus will reach conscious awareness. Moreover, ERPs to the appearance of a fixation cross before the target predict its detection, further suggesting that cortical excitability level may mediate target detection. A novel theory of cortical inhibition is proposed in which increased power represents a "pulsed inhibition" of cortical activity that affects visual awareness.

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Received Aug. 20, 2008; revised Dec. 26, 2008; accepted Jan. 15, 2009.

Correspondence should be addressed to Tony Ro at the above address. Email: tro{at}ccny.cuny.edu

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