Exploratory MEG study of the illusory contour perception: positive and inverted effects

The illusory contour is one of the most often used models in studies of Gestalt perception. In our MEG study we observed the so-called illusory contour effect (IC-effect): the activity of nonprimary visual and associative cortical areas was increased during the 150-250 ms time window after a stimulus onset in response to illusory stimulus, compared with the control stimulus. In addition to the positive IC-effect, the inverted IC-effect was revealed for the first time in adults. In our study it was manifested during the 60-120 ms window after the onset of stimulus. The inverted IC-effect is an early decrease in the activity of the visual cortex in response to the illusory contour compared with the control stimulus. The mechanism of the inverted IC-effect is yet unclear. The “bottom-up” and “top-down” hypotheses of the origin of the inverted IC-effect are discussed.