The effect of successive contrast on perceived size

The successive contrast effect demonstrates how contrast between an object and its background affects its perceived lightness. For example, a neutral grey square is perceived as lighter when presented on a dark background compared to a square of the same grey presented on a lighter background. In extension to these findings, we designed an experiment to test the effect of successive figure-ground contrast on perceived size. In a series of two-interval forced choice experiments, we asked participants to identify the larger of two neutral grey discs presented on either a lighter or a darker background at 3 different contrast levels. In all cases, we find that the perceived size of the disc on a light background is negatively correlated with the perceived size of the same disc on a dark background. This indicates a hitherto unreported relationship between scene contrast and size perception. We further speculate that this effect may contribute to size illusions such as the Ebbinghaus and Delboeuf illusions.