What is an optical illusion?
405471
An optical illusion is characterized by visually perceived images that are deceptive or misleading [1]. Information gathered by the eye is processed by the brain to give a perception that does not tally with a physical measurement of the stimulus source. A conventional assumption is that there are physiological illusions that occur naturally and cognitive illusions that can be demonstrated by specific visual tricks that apparently show particular assumptions in the human perceptual system [2].\n\nhttp://en.wikipedia.org/wiki/Optical_illusions\n\nHistory of Optical Illusions\n\nEpicharmus and Protagorus are the two people who invented optical illusions.  They lived around 450 B.C. and believed that our senses (seeing, hearing, smelling, tasting, and touching) were not paying enough attention and were messing us up when we would look at something weird. Epicharmus said exactly “The mind sees and the mind hears. The rest is blind and deaf.” Protagorus didn’t believe that what Epicharmus said was true. He thought that our senses and bodies were fine. He believed it was our environment that was messing us up. His words were “Man is nothing but a bindle of sensations.” \n\n         Aristotle thought that both Epicharms and Protagorus were both right and wrong. Aristotle lived around 350 B.C. and said our senses can be trusted, but easily be fooled. \n\n         Plato, who lived around 300 B.C., said our five senses need our mind to help to understand what they see. What he is saying is that the eyes and mind need to work together. That is what most people think now.\n\n         It took a while for people to realize optical illusions again. Then in 1829 a psychologist named Johannes Mueller wrote two books about visual illusions. He was the first person to call distortions visual illusion. That is why most people knew what he was talking about in his books. Then in 1854 another psychologist named J.J. Oppel finished where Johannes Mueller left off. He made a paper that had 10 pages of line illusions. Nobody had seen one of them until J.J. had published it in the paper. As soon as the people saw them, they became very popular. Almost everyone liked it for a while. It was so popular that an illusion was made called the MuellerLyer illusions. Also 12 theories were made to explain it.\n\nhttp://www.tqnyc.org/NYC052034/History.htm
318739
A mirage, derived from the Latin mirari, meaning 'to be astonished', is an optical phenomenon which often occurs naturally. The kind most commonly seen (known as inferior mirage, because the inverted image lies below the upright one) is produced by the refraction of light when it passes into a layer of warm air lying close to a heated ground surface (see highway mirage). This is an example of gradient index optics.\n\nFor more info:\nhttp://en.wikipedia.org/wiki/Mirage
612793
For me it was David Copperfield's illusion that made the Statue of Liberty disappear. I had the pleasure of meeting a magician that assisted with that one. I didn't ask him how it was done because I knew he wouldn't tell me anyway..lol. I think I know how it was done but none the less it was dynamic and wonderful to see.\n\nIf you are not familiar with this one, It's been a long time since I've seen it but I think it went like this...\n\nThe illusion was done at night. A stage was created for people to witness the illusion. They were seated on bleachers similar to ones you see in schools. Cameras were stationed around the statue. Helicopters flew around with cameras on board. David introduced the illusion. The lights went out and fireworks were in the air. The lights came back on and there was no statue! I believe the base was still visible but the statue was gone. Coooool...\n\nCan you guess how it was done?
507845
They call it misdirection. What the mind sees thinks is real. When they show you one thing they are secretly doing something you wouldn't know what to look for on the side to get the awe inspiring effect. Only other magicians or people on the "know" can understand. Scientifically, the whole world would know if Chris Angel really levitated or he'd be locked in a jar for Military research and we would never see something like that for real.
652068
Its an optical illusion caused by the surrounding geography  and is termed a gravity hill.  The most important factor contributing to the illusion is a completely or mostly obstructed horizon—without a horizon, judging the slope of a surface is difficult, as a reliable reference is missing. Objects one would normally assume to be more-or-less perpendicular to the ground (such as trees) may actually be leaning, offsetting the visual reference.  While humans also have a sense of balance to determine the inclination of the ground, visual clues can override this sense, especially if the inclination is shallow.
955445
called form of distortion is 'geometric distortion', which arises when a three-dimensional object is projected on a flat plane. For instance, a sphere in the image center is rendered as a round disk on the film, while a sphere in the image periphery of a lens with a large angle of view is elliptically elongated. \n\nExample: An Unnatural bowing of straight lines or other distortion of shapes, especially at the sides and corners in a TV picture.
1059024
NO, the hand is quicker than the eye, they are just clever at illusion.
1168605
An hallucination is a sensory perception experienced in the absence of an external stimulus, as distinct from an illusion, which is a misperception of an external stimulus. Hallucinations may occur in any sensory modality - visual, auditory, olfactory, gustatory, tactile, or proprioception (sense of balance and position in space).
1148084
Its all about illusion and distracting the eye. Our minds are easilly tricked.
370940
The Human brain put images together because they have learned to expect things, and sometimes the data might get a little confused. \n\nWe may see an illusion because we know what we are expected to see, even though part of a picture or design may not be completely there. The basis of this is in how we perceive things. \n\nThat almost explains everything right there. If our brain and eyes did not function like they do, we would not see illusions like we do.\n\nOne example of optical illusion is the television. The television is just shows us a continuous flow of still pictures, one right after the other. Our eyes along with your brain fill in all of the empty spots. Our brain has learned to expect movement. As a result, our brain can fill in all of the missing pieces and the television appears to be actually moving to you, even though it really isn’t! \n\nA computer monitor is also one big optical illusion. Sometime when you have a chance, look at a computer screen really close for a minute or two. You will notice that you computer screen is made up of tiny red, green, and blue dots. The illusion is, you see more than just red, green, and blue dots; you see thousands of different colors. Our brains put the red, green, and blue dots together to make the colors. \n\nOptical illusions just trick you into seeing something else. They are an error in our perception of the illusion.
59683
Here is an excellent site about optical illusions:
284388
I read one article before about something like that in an encyclopedia. I believe it's called the strobe effect.\n\nGomen ne, I am no science whiz but I found this more detailed article. Hope this helps.
1026711
There is a physical condition that makes you see odd things, a common one is an object floating in the sky. Try the Fortean website, \nwww.forteantimes.com\n\nA friend of mine sees Bruce Lee, dressed as in Enter the Dragon.
589971
The true magic is his ability to make illusion seem real. It is all a trick, but boy what a trick.
525237
No, unless it's a magic trick and only an illusion.
1168371
An optical phenomenon that creates the illusion of water, often with inverted reflections of distant objects, and results from distortion of light by alternate layers of hot and cool air. Also called fata morgana.
261824
Electric Brae is a famous optical illusion based on the surrounding geography being tilted so the the road on the hill appears to be level.