Reversed Café Wall illusion with missing fundamental gratings

The direction of Café Wall illusion was measured for ordinary Café Wall figures comprised of blocks with a square wave profile and for those with a missing fundamental (MF) profile. For the MF version, it was found that the illusion direction alternates according to the patterns' main component frequency when the shift between adjacent rows was systematically varied. The direction of illusion for the MF version was opposite to that for the original version when the phase shifts of adjacent rows were between 60 and 120degrees of the original grating. The results indicate that the illusion depends on the physical component rather than the appearance of the pattern. The possibility of the Café Wall illusion being mediated by low-level luminance mechanisms each tuned to a different spatial frequency is discussed based on the results.