Optical illusions

Optical illusions

 "Illusions we make are always more serene than reality, because from even our need, they should be fully appropriate to it, which is never reality. "John Slavici

Optical illusions occur as a result of how information is received through the eyes and how that information is interpreted in the brain.
When light enters the eyes, it passes first through the cornea, a transparent cover, and then through a watery fluid called the aqueous humor, and through the pupil, which is an opening in the colored part of the eye called the iris. The size of the pupil increases when there is less light and decreases when there is more.

 Light next passes through the lens, which focuses the light through a transparent jell, called the vitreous body, onto the retina. The retina has two types of light sensitive cells, rods and cones. Rods are particularly sensitive to shades of light and outlines, and they are important in both night and peripheral vision. Cones have specialized pigments that are sensitive to either red, green, or blue. Cones enable people to see details. Rods and cones cover the entire retina except for a small area just above the optic nerve, known as the blind spot.
When a person looks at an object of a particular color for a long time and then suddenly looks at a blank space, the person sees a ghostly outline of the object in its complimentary color. If the object is red, the person sees green. If the object is blue, the person sees yellow. This happens because the cones are sensitive in pairs. When a cone sensitive to one color is turned off, the other color is briefly turned on.

When someone looking at optical illusions, the eyes are recording an image that the brain misinterprets.

 The illusion is a false perception of an object, which, unlike hallucination occurs in this object. However, erroneous perceptions are considered only if the illusion is valid for a large number of individuals. Illusions common to all individuals with a normal psychophysiological state are determined by the very laws of perceptual training.

 Just as it perceives colour and brightness constancies, the brain has the ability to understand familiar objects as having a consistent shape or size.

 Physiological illusions, such as the afterimages following bright lights, or adapting stimuli of excessively longer alternating patterns (contingent perceptual aftereffect), are presumed to be the effects on the eyes or brain of excessive stimulation or interaction with contextual or competing stimuli of a specific type—brightness, colour, position, tile, size, movement.

 Cognitive illusions are assumed to arise by interaction with assumptions about the world, leading to "unconscious inferences", an idea first suggested in the 19th century by Hermann Helmholtz. Cognitive illusions are commonly divided into ambiguous illusions, distorting illusions, paradox illusions, or fiction illusions.

 Illusions can be based on an individual's ability to see in three dimensions even though the image hitting the retina is only two dimensional. The Ponzo illusion is an example of an illusion which uses monocular cues of depth perception to fool the eye.

There are three main types: literal optical illusions that create images that are different from the objects that make them, physiological ones that are the effects on the eyes and brain of excessive stimulation of a specific type (brightness, colour, size, position, tilt, movement), and cognitive illusions, the result of unconscious inferences.

"No illusion, no nothing, it's strange to know the mystery of reality in unreality." Emil Cioran