Size induction transcends the cardinal directions of color space.

Certain psychophysical phenomena occur separately for color and for luminance stimulation. Separate psychophysical effects have also been elicited along different directions in equiluminant colour space. Whereas in most studies in which separate luminance and color effects have been reported the authors have used successive-adaptation approaches, less is known about the separateness of color and luminance processing under simultaneous conditions. A study is reported in which simultaneous size induction was examined for several different color directions thought to be 'cardinal' for early stages of processing. The perceived size of a test object was influenced by the size of the surrounding objects regardless of the color direction of the test and induction objects. The results indicate that simultaneous size induction occurs at a level of processing at which information conveyed by color and by luminance mechanisms is compared and contrasted to influence visual perception.