An optical illusion (also called a visual illusion) is an illusion caused by the visual system and characterized by a visual percept that (loosely said) appears to differ from reality. Illusions come in a wide variety; their categorization is difficult because the underlying cause is often not clear but a classification
proposed by Richard Gregory is useful as an orientation. According to that, there are three main classes: physical, physiological, and cognitive illusions, and in each class there are four kinds: Ambiguities, distortions, paradoxes, and fictions. A classical example for a physical distortion would be the apparent bending of a stick half immerged in water; an example for a physiological paradox is the motion aftereffect (where despite movement position remains unchanged). An example for a physiological fiction is an afterimage. Three typical cognitive distortions are the Ponzo, Poggendorff, and Müller-Lyer illusion. Physical illusions are caused by the physical environment, e.g. by the optical properties of water. Physiological illusions arise in the eye or the visual pathway, e.g. from the effects of excessive stimulation of a specific receptor type. Cognitive visual illusions are the result of unconscious inferences and are perhaps those most widely known.
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This one was a little more difficult for me. Depending on which side of the brain you are using, you can change the direction (clockwise or counter-clockwise) the dancer is spinning just by focusing. It helps if you just stare at the feet if you're having trouble.
Contributed by Jordan See
If you didn't know, this picture of a dress is going viral all over social media. Depending on the person viewing the photo, they may either see the color of the dress as being black/blue or white/gold. Personally, I see the dress as being black/blue. But if you don't believe me, show this picture to 4 other people and chances are they will see a different color than you! There are many theories that try to explain this incredible phenomenon, however I attached the link to a site I believe to be very informational! Check it out and come up with your own conclusions for this incredible optical illusion!
Contributed by Adam Trujillo
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