You may have heard the saying "Seeing is believing." We mean by this, that if you can see something, then you better believe that it is true. Or, that you may not believe something to be true until you have seen it with your own eyes.
Can you think of any time when this saying is not true- in which "seeing is not believing"? Can what you think your eyes are seeing actually be something else? Can our eyes be fooled?
Whenever you can fool your eyes and brain into seeing things that are not there, or missing things that are there, or seeing things differently than they actually are - we call these "optical illusions." There are many different types of optical illusions. Entire books and websites are devoted to them. Visit the local library and check out a book on the subject. Go online with your parents and search for some optical illusion websites and discuss what you see. We have listed some of our favorite optical illusion websites at the end of this article. Not everyone always sees the same thing in an optical illusion - find out what others see.
Luke Kim, 10, performs the optical illusion of creating a floating finger sausage.
The following activity works better with friends and or family to talk about what you see. These people are your "optical illusion buddies." Take turns doing the optical illusion and tell your optical illusion buddies what you see and discuss if what you see is real or an illusion. How can you test if what you see is an optical illusion or real?
Activity: Floating Finger Sausage
Things you will need
An open area with good lighting works best (either indoors or outdoors is OK).
Two eyes. If you wear glasses that will not affect this activity.
Two hands each with an index finger (other fingers will work also).
Steps to create the floating finger sausage
1. Stick out only your index fingers from each hand.
2. Hold your hands with the tips of your index fingers touching, in front of your face at a comfortable distance.
3. Make sure your index fingers are lined up, fingertips touching, and are horizontal.
4. Hold your head level, so both of your eyes are also horizontal.
5. Now, focus on a distant object behind your touching index fingers. Notice, but do not focus on your index fingers (this may take some practice to do).
6. Now - very slowly - move your index fingers horizontally away from each other to a distance of 2.5 cm (about 1 inch)
7. What do you see? Discuss what you see with your optical illusion buddies.
Note: Some very young children may not notice the floating finger sausage. This may be attributed to several things, such as not having the vocabulary to understand what they are looking for or not being able to not focus on their outstretched index fingers.
Extensions of the Floating Finger Sausage Illusion
- What if you turn both of your fingers over so that both index finger nails are facing you - what do you see? What if you only turn over one index finger - what do you see?
- Try holding both index fingers vertically (one index finger aiming to the floor and the other aiming to the ceiling) - what do you see? Holding both index fingers vertically, what do you need to do with your head to see the floating finger sausage illusion?
Check out the websites linked at right for some optical illusion fun.
~ Libby and Robert Strong and Richard Pollack work with the SMART Center, a hands-on science outreach and education organization in the northern Ohio Valley, the headquarters of which is located at the SMART-Centre Market, 30 22nd St., Wheeling. Visit them at www.smartcenter.org.