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Abstract:
Abstract: Perceived color is influenced by perceptual
organization. Here, whole-head MEG recordings are used to
investigate the physiological correlates of contextual influences
on perceived color. We used a version of an illusion (White's
effect) consisting of a checkerboard of blue squares superimposed
on a black and white square-wave grating. When the blue squares
overlay the black bars they are perceived as lighter but when
overlayed on the white bars, they appear darker. The white, black
and blue parts of the image were frequency tagged by flickering
each at a different frequency against a gray background.
Stimulus-evoked steady-state magnetic fields were recorded with a
MEG sensor array. The difference in stimulus-related brain activity
produced by the light versus the dark version of the illusion was
studied. Blue frequency power at sensors over parietal/occipital
areas was higher in the dark condition. No other power effect was
observed. In the dark condition a high correlation was observed
between the phase of the blue and the white signals, whereas no
correlation was observed between the blue and black signals. This
pattern of correlations was reversed in the light condition. The
change in phase correlation suggests that the difference in
brightness perception observed in White's effect maybe due to a
differential degree of interaction between neuronal populations
underlying the response to the different parts of the
image.97A
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