1.  An optical illusion is a way of tricking the brain to see something that may not be there.

2.  The human brain puts images together because it has learned to expect certain things.  Sometimes the data gets confused.

3.  Many people really enjoy looking at illusion.  They seem to love being fooled in this way.   Magicians use illusions all the time. In fact, magicians are sometimes referred to as illusionists.

4.  Somne experiments that are being done show that some mammals and birds are fooled by illusions in much the same way as people are.

5.  One of the oldest known illusion related to touch was described by Aristotle more than 2,000 years ago. If you cross two adjacent fingers and then touch an object such as a pen, with both crossed finger tips at the same time it will feel as though you are touching two pens, not one.

6.  another illusion is the silverware and tablecloth at dinner.  When you touch both, the silverware appears to be colder than the cloth.  The fact is, however, they are both at room temperature. This is because metal conducts heat away from your finger more rapidly that cloth does.

7. Some illusions can actually be dangerous. Our sense of equilibrium or balance is located in the inner ear but it works closely with our visual world. When the pilot of an aircraft is flying at night or in a cloud and has no visual reference points it is possible for the pilot to become disoriented. He or she cannot tell whether the plane is gaining or loosing altitude, or turning left or right. This is called vertigo. It is an illusion, and pilots are trained to never rely on their sense of position but to respond entirely to the plane's instruments.

8.  When we go to the movies we are actually experiencing an illusion.  Nothing is really moving as we experience the film except a series of still photographs on a reel of film. Each is exposed for only a very short time and our eyes and brain do not see the separate still shots.  Our brains see the figures on the screen moving. 

9.  Another illusion we experience at the movies involves the sound.  When we look at the characters on the screen, it appears the sound is actually coming out of their mouths.  the reality is that the sound is coming out of speakers throughout the auditorium we are sitting in.

10.  A computer monitor is also an optical illusion. The 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.