Hering Illusion

The Hering illusion is a shape distortion visual illusion where two perfectly parallel and vertical lines, when drawed on a background of converging lines, appear to bow outwards.

This effect was discovered in 1861 by the German physiologist Ewald Hering: it is caused by the depth perception induced by the converging lines, which in turn changes the perception of the vertical lines.

Two illusions share the same mechanism of action: the Orbison illusion and the Wundt illusion (which is a Hering in reverse).

Hering illusion: the red lines seem curved, but they are really vertical and parallel