Illusory contours and the ends of lines.
A series of lines pointing towards a central region induces an illusory brightness effect that is systematically related to the angle formed by the lines and the contour of the illusory brightness. As the lines veer to become tangents the illusory brightness decreases.
D000328:Adult; D002648:Child; D004215:Distance Perception; D005556:Form Perception; D006801:Humans; D007088:Illusions; D008027:Light; D009903:Optical Illusions; D012858:Size Perception