Attractive Contours of the Ebbinghaus Illusion.

There is debate as to whether or not the Ebbinghaus illusion is driven by high-level cognitive size contrast mechanisms as opposed to low-level biphasic contour interactions. In this study, we examine the variability in effects that are shared between this illusion and a different illusion that cannot be explained logically by a size contrast account. This comparison revealed that nearly one quarter of the variability for one illusion is shared with the other - demonstrating how a size-contrast account cannot be the sole explanation for the Ebbinghaus illusion.