Abstract

Objective

In this project, you will investigate the perception of apparent motion by making flip-book animations.

Introduction

Do optical illusions trick your eyes or your brain? That is a question scientists were trying to answer for centuries! The answer is, it's a little bit of both since the eyes and the brain work together during the perception of vision. Have you ever heard the phrase, "Seeing is believing?" Well, it's more accurate than you might think! During the perception of vision, your eyes see an object and send the information to the brain, where it is processed, forming the image that you see.

Optical illusions are scientific, but also just plain fun! One optical illusion that has had a huge impact on our culture is the illusion of apparent motion. You perceive this illusion every time you watch cartoons or a movie. You perceive that the characters on the screen are moving around, but in fact you are seeing many still pictures flashing before your eyes! Your brain puts all of the pieces together and fills in the blanks to make it look like fluid movement. How does this work?

"Scientists say your brain fills in the gaps to create smooth motion because it is trying to make sense of what you are seeing. You don't even need an optical toy to experience this phenomenon; it happens constantly—every time you blink. The reason you don't notice blinking as a black screen is that your brain fills in the brief dark period with a reasonable assumption about what happened when your eyes were closed. Similarly, when you look at an image of an object, a split second of blankness, then an image of the same object in a new spot, your brain fills in the gap, and you "see" the object move." (MarthaStewart.com, 2007)

The process of making an animated feature film is long and involved, sometimes taking several years! But there are a few very simple devices you can make to investigate apparent motion: (Rich, B.W., 2006)

• Flip-books are stacks of heavy-weight paper that are held together with binder clips. Each page in the stack has a slightly different variation of the image on the previous card. When you quickly thumb through the deck, your brain assembles the series of images into movement.
• Thaumatropes (THAW-muh-tropes) are made by mounting two images on either side of a disc. Usually the two images go together, like a bird and a cage, or a fish and a bowl. When you rotate the disc, the images from the two sides come together into one image!
• Phenakistiscopes (fuh-NAH-kih-stuh-scopes) are discs decorated with a pattern that "moves" when you spin the disc. You can create animations by drawing a series of images around the outer edges of the disc.
• Zoetropes (ZOH-ee-tropes) are similar to phenakistiscopes, except they take the shape of a cylinder instead of a disc. The images are placed along the inside wall of the cylinder, and when you spin the cylinder, you see the animation.

In this experiment, you will try to break the limits of apparent motion. You can test this by making flip-books out of index cards, mini binder clips, and sticker dots. Each flip-book will have a series of dots that shift a certain distance from card to card, resulting in the perception of "moving" dots. By spacing the "moving" dots farther and farther apart, you can find out when the brain stops perceiving apparent motion. As the dots become farther apart, when will your volunteers NOT perceive them to be moving?

Terms, Concepts, and Questions to Start Background Research

To do this type of experiment, you should know what the following terms mean. Have an adult help you search the Internet, or take you to your local library to find out more.

• Perception
• Apparent motion
• Optical illusion
• Flip-book
• Thaumatrope
• Phenakistiscope
• Zoetrope

• Why do we perceive apparent motion of stationary objects?
• How is the brain tricked into filling in the blanks?
• Are there limits to our perception of apparent motion?

Bibliography

• Let Martha show you how to make your own flip-book, thaumatrope, or phenakistiscope:
  MarthaStewart.com. (2007). Paper Movies. Martha Stewart Kids. Retrieved December 6, 2007 from http://www.marthastewart.com/paper-movies
• The Saturday Scientists explain four simple animation devices based upon apparent motion and the persistence of vision:
  Rich, B.W. (2006). Animation Devices. The Saturday Scientists. Retrieved December 6, 2007 from http://www.west.net/~science/animate.htm
• This experiment is a simpler version of the Apparent Motion lesson from CogLab, an online laboratory manual for studying cognitive psychology:
  CogLab. (2007). Apparent Motion CogLab 2.0 Online Laboratory. Wadsworth Publishing. Retrieved December 6, 2007 from http://coglab.wadsworth.com/experiments/ApparentMotion.shtml
• This site has a java applet you can use to make printable, color graphs of your data:
  NCES. (2006). Create a Graph. National Center for Education Statistics (NCES) U.S. Dept. of Education. Retrieved December 6, 2007 from http://nces.ed.gov/nceskids/createagraph/

Materials and Equipment

• Mini binder clips (4)
• Half-size (3x2.5 inches), lined index cards (100 halves)
• Small, colored sticker dots (like Avery 1/4" Round Color Coding Labels, Rainbow Pack, #05795) (100)
• Volunteers

Experimental Procedure

1. First, cut your 3x5 index cards in half to make half sizes (3x2.5-inch cards).
2. Then make four stacks of 25 half-sized index cards each.
3. Next, you will take each stack and make a series of "animated dots" along the right edge of the cards by placing one dot on each card. Each colored series of dots should be spaced differently (one space, two spaces, three spaces, or four spaces), allowing you to test for the perception of apparent motion in your volunteers by showing them the series of flip-books. You can use the lined spaces on the index cards as a guide for placing your dots. Here is one example of a dot series in the color blue, which skips two spaces per card:

4. Here is the overall scheme for making the entire series of flip-book decks in four colors:
   1. Red - Move the red dot one space down or up along the edge in a stack, until you reach the end of the deck.
   2. Blue - Move the blue dot two spaces down or up along the edge in a stack, until you reach the end of the deck.
   3. Yellow - Move the yellow dot three spaces down or up along the edge in a stack, until you reach the end of the deck.
   4. Green - Move the green dot four spaces down or up along the edge in a stack, until you reach the end of the deck.
5. Neatly stack each deck and assemble the flip-book by attaching a mini-binder clip to the left side of each of the four decks. Your assembled flip-books should look like this:

6. Now go find some volunteers so you can have them flip through your flip-books!
7. As your volunteers flip through each book, ask them if they see the dot move, if they see it jump, or if they see it flash. Indicate their response in a data table. Here is an example of a data table you could use during this experiment to tally your results:

   Color	Spaces	Moving	Jumping	Flashing
   Red	1
   Blue	2
   Yellow	3
   Green	4

8. Graph your results on a bar graph. As the number of spaces increases, does the perception of motion also change? How?

Variations

• In this experiment, you tested whether the variable distance between objects had an effect on apparent motion. Two more variables you can test for are:
  • Frequency - Will flipping the cards faster or slower make a difference? Have your volunteers flip the books at different speeds. What happens to your results?
  • Size - Do larger objects work better than smaller objects? Change the size of the dots and find out.
• Design a project investigating the practical application of apparent motion to animation. Can you use the results of your experiment to design better animations?
• Do your results with the spacing of objects in the flip book also apply to thaumatropes, phenakistiscopes, and zoetropes? Test and find out.
• Advanced students who have experience in programming can turn this project into a computer science project. See the Science Buddies project Follow the Bouncing Ball: A Web Animation Project to find out more.

• For more science project ideas in this area of science, see Human Behavior Project Ideas.

Credits

Sara Agee, Ph.D., Science Buddies

Last edit date: 2008-02-20 22:00:00