Optical Illusions

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An optical illusion involves images that are sensed and perceived through the visual system and misinterpreted in the brain. Whereas the brain can process some of the attributes of the object, there are features of the object that are misleading and therefore lead to errors in the perceptual process.

There are three generally recognized types of optical illusions. These are the literal illusions, cognitive illusions and physiological illusions.

Literal Illusions

A literal illusion is an optical illusion that tends to make images that vary from the objects that form them. Below is an example of a literal illusion.

Cognitive Illusions

A cognitive illusion refers to the type of illusion that distorts the knowledge and assumptions of the experiencer towards a physical element or object and its environment. Dr. Herman Helmholtz, a German physician, suggested that a cognitive illusion emerges when there is an interaction with one's beliefs and assumptions of the world, resulting to unconscious inferences.

Most psychologists agree with the four types of cognitive illusions, namely: (1) geometrical-optical, (2) ambiguous, (3) fiction, and (4) paradox.

Geometrical-Optical Illusions

Geometrical-optical illusions are those that present distortions of the length, shape, size, curvature, and / or position. These are also called distorting illusions. Three popular distorting illusions include the Ponzo illusion, the Muller-Lyer illusion and the Cafe Wall illusions.

Ambiguous Illusions

Ambiguous illusions are images of objects that trigger a switch between possible alternatives in the perceptual level. These illusions include the so-called "impossible objects". The most famous example of ambiguous illusion is the Necker cube, as viewed below.

Fiction Illusions

Fiction illusions are illusions that elicit perception of a figure that is not actually present in the stimulus. Below is an example of a fiction illusion.

Paradox Illusions

Paradox illusions are those that are made by paradoxical or improbable objects. The Penrose triangle is an example of a paradox illusion, as seen in the following image.

Physiological Illusions

With physiological illusions, the brain presumes that the image is an effect of excessive interaction or stimulation of a physical stimulus. This stimulus can be either competing or contextual of a particular aspect of color, brightness, size, movement, etc.

Full reference: 

(Sep 10, 2013). Optical Illusions. Retrieved May 18, 2019 from Explorable.com: https://explorable.com/optical-illusions

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