Illusions have been on the games and quiz cards of our lives for long. Seldom do we think about the causes of an illusion. When you see the piece of paper that contains a tricky drawing on it, and on more careful observation, you also see there is a hidden picture or illusion in the drawing. Now that is magic! Is it really? Well, yes it is, but it is the magic of the calculations that take place between your eyes and your brain. Confused? Let us understand in detail about an optical illusion. Scientifically, it can be defined as, images perceived by our eyes, but which are different from the actual physical structure of the images. The images differ from the objective reality when perceived. This is also termed as visual illusions. When we look at an object, the retina scans the image and sends nerves impulses to the brain. The brain then interprets the image, and then the actual perception takes place. Sometimes, the perception that is signaled by the brain, does not match the physical structure of the source that stimulates the image. At such a time, you will see an image that is not there or an image that is a part of the picture but not the whole. You may also see one or both images in the illusion. These are interesting facts that create the space, for understanding the calculations and the functioning of the brain. And also understanding the way our visual brain fails at times to capture the physical world around, and the mystery behind the functioning of the brain in a particular fashion, in case of illusions. There are different types of optical illusions, and we will discuss in detail about each, in the following. Different Types Of Optical Illusions Optical illusions are of three major types. Mainly, literal, physiological and cognitive illusions. We have facts about each type listed below.

Literal Illusions:	These are the simplest of all and are characterized by, the difference in the image (of what is perceived) and the actual physical objects that make the picture. That is, the picture will give you a different illusion instead of the actual objects in the picture.
Physiological Illusions:	When the eyes or the brain get stimulated in excess by a particular type of stimulation, mainly like motion, color, brightness, tilt, etc. These illusions are usually the afterimages, that are created due to the stimulation of the vision by a specific path of movement, or brightness and even by the stimulation of extreme long patterns in the image that keep alternating (which is also termed as contingent perceptual aftereffect). This type of illusion can be explained as - in the first stage of visual processing, the stimuli follow a dedicated neural path, and when this stimulation of an only specific type of its channel, like brightness, color or dimension is repeated, a physiological imbalance is created, that affects and alters the perception.
Cognitive Illusions:	These type of illusions are very common but are interesting too. They are even designed specially for kids. Cognitive illusions unlike others, are based on the interaction with different levels of perceptual processing and not physiological processing. In this type of illusion the brain relates the objects in the image to the built in assumptions or knowledge. This illusion is assumed to be a result of interaction of the brain with the assumptions or knowledge it has stored about the world. Cognitive illusions are further classified in three types. Each is described in the following:
➣	Ambiguous Illusions	These types of illusions define objects or images that will be perceived with different appearance of views or images. The perceived image in the brain will keep alternating or 'switching' between the possible illusions of the images in the picture. What the eyes will see, will not be a single view, but with alternating visions to the eye, there is alternative functioning of the perception process in the brain.
➣	Distorting Illusions	These illusions are based on the alterations of the physical aspects like the size, curve or length. In these type of images you will feel the dimensions of the objects in the picture are changing in length, shape or size, instead of remaining constant.
➣	Paradox Illusions	These illusions, just like the name suggests, contradict its concluded vision. They are generated by objects that are fictitious or paradoxical, to form in real life, or in three dimensions, but they appear to be apt and convincing enough and perplexed in two dimensional images. These illusions are based on the theory that describes the cognitive (based on all that is learned and understood) misunderstanding, which is that the edges that are adjacent must always join.
➣	Fictional Illusions	These illusions are defined as the vision or perception of an image or object by an individual in a different way, than what it could be perceived by other individuals. This is also termed as schizophrenia or hallucinations.
Our brain is an interesting processor that stores information and tries to recall and relate it, to all that gets perceived by the eyes. During this, it may put all the information like a puzzle and try to fill each gap with all that is learned and stored. Sometimes, it may not fill it with what we really see. It may process the image based on its knowledge and possibilities that may not even be real in the actual world.

This was all about the different optical illusion types. Some of these illusions are created mostly for research, so as to understand the human brain and the exact effect of its functions and processing, in various alternating patterns of vision.