Ehrenstein variations.
Radial lines pointing towards a central circular region induce an illusory positive brightness contrast. Shift in line orientation from radial to tangential can result in negative brightness contrast and line enhancement.
D004192:Discrimination, Psychological; D005556:Form Perception; D006801:Humans; D007088:Illusions; D009903:Optical Illusions; D010364:Pattern Recognition, Visual; D011601:Psychophysics