Optical Illusions

Let's have a bit of rest. Do you like optical illusions? I am really keen on them. Here are some good images I found for you.

This is a painting with numerous hidden faces. How many can you find?

There are several hidden faces in this image. How many can you find?

This one is very simple but quite amazing, Move your eyes around the image below. That's almost enough to make your head spin. The movement is just an illusion. it gives headache, doesn't it?

This is a very strange image taken from www.cyberium.net

Another funny work from www.cyberium.net/
In the same "surrealistic tendency", there is the great Salvator Dali...You can view many of his paintings on www.universdali.com. The Belgian artist René Magritte, another surrealistic painter has also realized many works that are related to optical illusions. See his works on http://www.magritte.be.
Optical illusions
An optical illusion characterized by visually perceived images that, at least in common sense terms, are deceptive or misleading. Therefore, the information gathered by the eye is processed by the brain to give, on the face of it, a percept 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 say something more basic about how human perceptual systems work.
Cognitive illusions
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.
Ambiguous illusions are pictures or objects that elicit a perceptual 'switch' between the alternative interpretations. The Necker cube is a well known example; another instance is the Rubin vase.
Distorting illusions are characterized by distortions of size, length, or curvature. A striking example is the Café wall illusion. Another example is the famous Mueller-Lyer illusion.
Paradox illusions are generated by objects that are paradoxical or impossible, such as the Penrose triangle or impossible staircases seen, for example, in the work of M. C. Escher. The triangle is an illusion dependent on a cognitive misunderstanding that adjacent edges must join.
Fictional illusions are defined as the perception of objects that are genuinely not there to all but a single observer, such as those induced by schizophrenia or hallucinogenic drugs. These are more properly called hallucinations.
A possible explanation of many visual illusions
The explanation of illusions is widely debated. Recent evidence implies that visual illusions are simply the signature of the empirical statistical way all visual percepts are generated. In this interpretation, these phenomena are simply a consequence of the way vision has evolved to solve the inverse problem (see references and links below).

References : www.michaelbach.de , http://en.wikipedia.org/
You can find all this funny stuff on this Website : http://www.humoronline.com
Another site with unusual optical illusions is this one: