English: Here are two relative size illusions described by Italian visual researcher Gianni A. Sarcone in 1997 and 2013.The first relative-size illusion called Sarcone’s Crosses contradicts Ebbinghaus illusion (aka Titchener Circles, 1898) and Obonai square illusion (1954).Sarcone's cross illusion consists of a cross (the test shape) surrounded by sets of squares of distinct size (the inducing shapes). As shown in the diagram, the three blue crosses in fig. 1.a, 1.b and 1.c are exactly the same size; however, the one on the left (fig. 1.a) appears larger. The illusion works even when the small squares completely occlude the blue cross (see fig. 1.c).

In conclusion, there isn’t always correlation between the size of the surrounding shapes and the relative size perception of the test shape.

In fig. 2.a and 2.b, by effect of assimilation, the diagonal red line within the large ellipse seems subjectively longer, but in fact the blue line is objectively the longest of both lines.