The Orbison illusion is an optical illusion that was first described by the psychologist William Orbison in 1939. The bounding rectangle and inner square both appear distorted in the presence of the radiating lines.

The background gives us the impression there is some sort of perspective. As a result, our brain sees the shape distorted. This is a variant of the Hering and Wundt illusions.

The Poggendorff Illusion is an optical illusion that involves the brain’s perception of the interaction between diagonal lines and horizontal and vertical edges.

It is named after Johann Poggendorff (1796-1877), a German physicist who first described it in 1860. In the image above, a straight black and red line is obscured by a grey rectangle. The blue line appears, instead of the red line, to be the same as the black one, which is clearly shown not to be the case in the second picture.