Optical illusion is also called visual illusion. In this illusion, a person perceives images in a very different way than in reality. The eyes gather information and send it to the brain. The perception of the object for which the information is sent to the brain does not match with the physical attributes of the same object. Optical illusions can happen naturally or could be demonstrated by using some visual tricks which show some specific assumptions in the human perceptual system. Many of us have experienced or heard about mirage in desert areas which is a very good example of natural illusion and is an optical phenomenon. The size of the Moon varies for example it looks smaller when it is over the head and it looks larger when it is near the horizon. This is also an example of natural illusion but it is not an optical phenomenon but it could be categorized as cognitive or perceptual illusion.
The Herman grid or Necker tube is the example of Developed or discovered illusions. When we learn and understand these types of optical illusions, it becomes easier for us to understand the limitations of the visual system of the human beings. Sometimes people do get afterimages when they are exposed to bright lights then different types of physiological illusions are experienced. Another type of optical illusion which is quite well known and interesting is the Cognitive illusions. In this there is interaction between different levels of perceptual processing and the knowledge which is in-built gets misdirected. It is further classified into different subtypes. When the pictures or objects get switched between the alternative interpretations they show ambiguous illusions. Rubin vase or Necker cube are good examples for this type of illusion. When the objects are represented with distortions of length, position, size and curvature they create Geometrical-optical or distorting illusion. The good examples are Café Wall illusion, Ponzo illusion. Penrose triangle or impossible staircases are the example of Paradox illusions. Sometimes optical illusions are introduced due to schizophrenia or hallucinogenic medicines where a person hallucinates about an object which is not present there.
One of the tools which the neuroscientists use to understand the working of the brain to study how the brain has the sense of reality created is the optical illusion or the visual illusion. Earlier many visual artists and the illusionists used the optical illusions to create deep insight into the internal workings of the visual system of humans. Artists have been successfully used the techniques to fool the brain to make it think a flat canvas to be a three-dimensional one long before scientists finished studying the properties of neurons. Optical illusions are defined as the dissociation between how an object or an event looks physically and how it gets perceived subjectively. WE a person experience visual illusion, the person may see a thing which is not there or the person may not see a thing which is there. The person may see a thing in an entirely different way also. As there is a disconnection between the perception of an object or image and the reality, optical illusions are able to demonstrate the way in which the brain can fail to recreate the physical world. When all these failings are studied thoroughly, we are able to known more about the computational methods used by the brain to build visual experience.
There are many artists who are known to have worked with the concepts of optical illusions such as Bridget Riley, Salvador Dali, M.C.Escher, Marcel Duchamp, Victore Vasarely and Charles Allan Gilbert. Some modern artists who have tried out various experiments with the optical illusions are Ocatavio Ocampo, Shiegeo Fukuda, PAtrik Huges, Dick Termes, Rob Gonsalves, Ben Heine, Akiyoshi Kitaoka. In movies also, the concept of visual illusions have been used. There is a popular hypothesis about the Optical illusion called Cognitive processes hypothesis. It is considered as a framework to understand the optical illusions as the signature of the experimental statistical method of the evolution of vision to solve the inverse problems. Scientists and others have been working and experimenting on visual illusions a lot and all these will definitely help us to understand more about this interesting phenomenon of the human body.