Fraser Cords and Reversal of the Café Wall Illusion

Abstract

Morgan and Moulden have shown that the café wall illusion can be explained by the effects of processing with a difference-of-Gaussians filter which reveals Fraser twisted cords in the figure. It is deduced that their account leads to the novel prediction of the reverse tilt illusion if the width of the mortar lines is suitably increased. This prediction is confirmed by demonstration.