Ebbinghaus illusion

[1] The Ebbinghaus illusion has played a crucial role in the debate over the existence of separate pathways in the brain for perception and action (for more details see Two Streams hypothesis).

A study by neuroscientist Melvyn A. Goodale showed that when a subject is required to respond to a physical model of the illusion by grasping the central circle, the scaling of the grip aperture was unaffected by the perceived size distortion.

The illusion was found more often to cause relative-size deception in university students, who have high context-sensitivity, than in children aged 10 and under.

[7] The winner of the 2014 Best Illusion of the Year Contest, submitted by Christopher D. Blair, Gideon P. Caplovitz, and Ryan E.B.

In fact, the central test shape (a cross) surrounded by large squares appears larger instead of smaller.

The two orange circles are exactly the same size; however, the one on the right appears larger.

The three blue crosses are exactly the same size; however, the one on the left (fig. 1) tends to appear larger.