An optical illusion is any image that fools the observer’s eye and the brain. It causes someone to perceive something that it’s not actually there.
Optical illusion occurs to everyone with the ability to see. They can make the eye to send false image to the brain. What the brain sees differs from what the eye is seeing.
The concept of optical illusion was first used by the Greeks. They built their temples so that the roof was slanted. This gave the illusion that the temple was actually standing straight. The scientific study of illusions dates back to the beginning of the nineteenth century when scientists got interested in perception. Since then there has been enduring interest, and illusions have been used as tools in the study of perception.
There are two types of optical illusions physiological and physical or cognitive.
Physiological optical illusions are the kind that occurs after staring at a bright light for a few seconds. If you over-stimulate your vision by staring at a bright light and then close your eyes, you’ll “see” an afterimage of that light.
Physical or cognitive illusions can be divided on four different groups: Ambiguous illusions, Distorting illusions, Paradox illusions and Fictional illusions. I am going to describe every one of them with an example.
Ambiguous illusions are pictures or objects that elicit a perceptual 'switch' between the alternative interpretations. The Necker cube is a well known example; another instance is the Rubin vase. Rubin vase was discovered by the Danish psychologist Edgar Rubin. It has a vase and two faces. But we can’t watch both at the same time. When two fields have a common border, one is seen as figure and the other as background....