 This explanation throws into doubt the hypothesis that implies that altering luminance, motion, or spectral distribution of the field surrounding the target would not alter perception.The empirical findings also contradict the hypothesis that 'illusions of brightness' caused by contour junctions in the stimulus explain the Chubb illusion, as proposed by Anderson (1997).Visual illusions can be categorised into physiological/pathological, perceptual and ambiguous (bistable/multistable).