"Optical illusions are pictures that play tricks on your eyes and baffle your perception," according to Charles H. Paraquin in The World's Best Optical Illusions. But how do they fool us? How does it work?
Consider the phrase optical illusion. Optical has to do with the eyes and seeing. Illusion means something that appears in some way different than it actually is in reality. The science of optical illusion involves the study of the three elements that allow us to see: the eyes, the brain, and light. The eyes see something but it is the brain that helps us understand what we see. If the light is different it can also affect what our brain tell us. When we see a drawing our eyes see only lines, but the brain takes over and tries to make sense out of what we see. So, the eyes and brain work together with light to enable us to see. If any of these three elements is missing or unusual our brain is confused and an optical illusion is created.
One of the reasons that many illusions work is because we have two eyes that work together to send messages to the brain. If one eye sees something that does not agree with what the other eye sees, it confuses our brain. The movement of our eyes can also contribute to optical illusions. The eyes do not move up and down as easily as they move from side to side. This can make two lines of equal length placed perpendicular seem to be different sizes. The vertical line seems longer because of the way our eyes move. Our eyes can also be distracted, and then fooled, by either empty space or extra lines and shapes around an object. Consider the two inside squares below. Are they the same size?
It is easy to be fooled at first glance because the outside squares influence how we see the inside squares, but the inside squares are exactly the same size.
