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Katharina Schmack, Ana Gomez, Marcus Rothkirch, John-Dylan Haynes, Philipp Sterzer; Expectations alter the neural correlates of visual awareness in visual cortex. Journal of Vision 2011;11(11):209. doi: 10.1167/11.11.209.
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Top-down processes are well known to modulate sensory awareness. For example, endogenous attention enhances the access of visual information to awareness and is associated with increased neural activity in visual cortex. However, it is less clear whether top-down modulations alter the contents of awareness in a qualitative manner. We addressed this question by testing the effect of learned expectations on the neural correlates of visual awareness during bistable motion perception. In an fMRI experiment, participants viewed a random-dot-kinematogram perceived as a rotating sphere. During an initial baseline phase the stimulus was completely ambiguous, thus yielding bistable perception. Perceptual expectations were then induced in a subsequent learning phase, during which participants wore transparent glasses in two different orientations. Each orientation was associated with one dominant rotation direction of the stimulus, which was achieved by disambiguation through disparity cues. In the test phase we then probed how expectations associated with the glasses influenced perception of the ambiguous stimulus. We used multivoxel pattern analysis to decode perception from fMRI activiation patterns in visual cortex. A support-vector-machine classifier was trained on the baseline runs to assign each scan to a reported percept, and was then used to predict perceptual states from activation patterns during the test runs. Reported dominance times for the expected rotation direction were longer than for the unexpected direction. Strikingly, this behavioural expectation effect was mirrored by the activations patterns in visual cortex: Decoding of the perceived rotation direction during test runs with a classifier trained on the independent baseline data yielded a significantly greater proportion of expected than unexpected percepts. This neural expectation effect correlated with the behavioural expectation effect, indicating that it indeed reflected participants' subjective perception. These results show for the first time that experimentally induced expectations alter the neural correlates of visual awareness in visual cortex.
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