The question why we see optical
illusions is bound to be a mystery. Every once in a while a different scientist comes up
with a new theory, which is checked and tested, and ends up being another theory in the long list. One of the many theories is that the eye does see optical
illusions but the brain uses experiences and memories to interrupt them. The idea behind this theory is basically that are brain is build up to face and interrupt large objects and works perfectly once facing three
dimensional objects (from the "natural" surroundings). But what makes optical illusions so "illusionary" are lines and contextual information that our visual system takes as clues to figure out the locations of objects in the three dimensional world. In optical illusion the brain identifies those false clues as real objects. Optical illusions use and are based on different things; lines, changing images, brightness and contrast, depth and length, and colors of course.