Modeling Geometrical Mysteries of Cafe Wall illusions

This paper explores the tilt illusion effect in the Café Wall pattern using a classical Gaussian Receptive Field model. In this illusion, the mortar lines are misperceived as diverging or converging rather than horizontal. We examine the capability of a simple bioplausible filtering model to recognize different degrees of tilt effect in the Café Wall illusion based on different characteristics of the pattern. Our study employed a Difference of Gaussians model of retinal to cortical “ON” center and/or “OFF” center receptive fields. A wide range of parameters of the stimulus, for example mortar’s thickness, brightness, tile contrast, phase of the tile displacement, have been studied. Our model constructs a multiple scale edge map representation that reveals tilt cues and clues involved in the illusory perception of the Café Wall pattern. We will show here that our model not only can detect the tilt in this pattern, but also can predict the strength of the illusion and quantify the degree of tilt. The results of our simulations are consistent with previous psychophysical findings across the full range of Café Wall variations tested. Our results also suggest that the Difference of Gaussian mechanism is the heart of the effects explained by, and the mechanisms proposed by the Irradiation, Brightness Induction, and Band-pass filtering models.