Visual Illusions have always been a curiosty to the human eye. They are a way of demonstrating how our visual system can be "tricked" into seeing things that are not really there or inaccurately seeing things. There are many types of illusions that we have been introduced to through out this semseter. Mach Bands, which small changes in lightness are seen near boarder even though no changes are present in the physical pattern of the light. There is also White's Illusion whoch is when two physically identical fields can appear diffrent. The Herman Grid, is when two alternating scenes appear similar even though there are diffrences between them, this is another illusion. There are many more these are just a few interresting ones.
http://www.illusion-optical.com/Quiz/ Take this you will be shocked!