Optical illusions are characterised by perceived images that differ from objective reality. Information that is given to the eye is processed by the brain to give a perception of reality. Sometimes, the brain gets things slightly confused and this results in it interpreting things differently to how they actually are. There are a number of famous optical illusions and this article details five of them.
The Chubb illusion
The Chubb illusion is an optical illusion in which the apparent brightness of an object varies dramatically depending on how it is presented. For instance, a dark object surrounded by darker objects may appear brighter than an actually brighter object, surrounded by even brighter objects. This was observed and documented by Chubb and colleagues in 1989.
The Hermann grid illusion
The Hermann grid illusion is a very cool optical illusion that produces the illusion that there are grey spots or squares at the intersections of black squares within the grid. This works as the eye struggles to separate the black colour of the squares from the white intersections resulting in white blurs in between the squares.
The Hering illusion
The Hering illusion is an optical illusion discovered by the German physiologist Ewald Hering in 1861. It consists of two straight horizontal lines that look as if they are bowed outwards. This distortion is produced by the lined pattern on the background that simulates a perspective design, and creates a false impression of depth. When looking at this illusion you may note that the thinner straight line appears more bowed than the thicker straight line.
The Jastraw illusion
The Jastrow illusion is an optical illusion discovered by the American psychologist Joseph Jastrow in 1889. In the illusion, two figures appear that are identical to each other with one sat upon the other. The illusion gives the impression that the lower figure appears to be larger than the one sat above.
The Ebbinghaus illusion
The Ebbinghaus illusion is named after its discoverer, Hermann Ebbinghaus and is an optical illusion of relative size perception. If two circles of identical size are placed next to each other and one is surrounded by large circles and the other is surrounded by small circles, then the second central circle will appear smaller than the first central circle.
