Half Moon Illusion


Incomplete contour erasure can affect the perceived brightness of a uniformly filled light grey disk.  First adapt to the flicker of the semicircle, presented superimposed on the left edge of the disk. Following flicker adaptation, not only has the left edge of the disk disappeared, but also a brightness gradient is apparent, making the disk appear like a half moon. In the absence of edge information on the left half of the disk, the brain appears to interpolate the brightness levels from the unadapted right edge to the background level.