The Zöllner illusion is another commonly demonstrated optical illusion. First discovered in 1860 by a German astrophysicist named Johann Karl Friedrich Zöllner, this illusion presents a series of oblique lines crossed with overlapping short lines. The oblique lines look as if they are crooked and will diverge. In reality, all of the oblique lines are parallel.
Much like the Muller-Lyer and Herring illusions, this optical illusion demonstrates how the background of an image can distort the appearance of straight lines. Several different explanations for the Zöllner illusion have been suggested. First, the angle of the short lines compared to the longer lines creates an impression of depth. One of the lines appears to be nearer to us; the other farther away. Another possible explanation is that the brain attempts to increase the angles between the long and short lines. This results in a distortion as the brain tries to bend the lines away and towards each other.
Interestingly, if the color of the lines are switched to green and the background to red, the effect completely disappears as long as the two colors are of equal brightness.