Can you spot the dot?
Have you ever wanted to make something disappear (maybe your homework!)? In this activity we will take advantage of the way your eyes and your brain talk to each other, to make colored dots seem to appear and disappear (sorry, it probably won’t work on your homework)!
You don’t realize it, but your eyes are constantly making small, jittery movements. This happens so quickly that we usually can’t see or feel it. The movements are called ‘saccades’ and they allow your eyes to constantly gather and update information to send to your brain. Among other things, saccades help us see edges, like the end of a table or the edges of an orange dot on a piece of red paper. It’s similar to if you use a computer to zoom in on a photo, and then scroll over the zoomed image. As you move, you gain more information about the image as a whole. Your eyes collect information with quick movements around your environment, and pass this information onto your brain. This works best when there is a high degree of contrast in your environment. In general, it’s much easier to see the edge of a doorway than it is to see the edge of a cloud. The doorway has very precise edges with high contrast, whereas a cloud can have irregular, blurry edges and less contrast.
In this activity we will see how blurry edges can cause problems for your eyes, and make things seem to disappear!
- 1 sheet each of red, blue, green and orange construction paper
- 1 sheet of wax paper (approximately 8 x 11 inches)
- A ruler
- A partner to help you measure and record during the experiment
- Cut each piece of construction paper in half
- Set one half sheet of each color aside (we’ll refer to these as the ‘large sheets’ in the instructions)
- Cut a 1 inch diameter circle from each of the other half sheets
- Take the large red sheet of construction paper and place it on a flat surface (table or countertop works best).
- Place the orange dot in the center of the red construction paper sheet.
- Place the wax paper down so that it covers the dot and sheet. Can you still see the orange dot?
- Slowly lift the wax paper away from the table and toward your face. Keep the wax paper parallel to the table, so that it continues to cover the dot and red sheet. Look through the wax paper to the colored paper below. What do you notice happening to the orange dot as you lift the wax paper?
- Raise the wax paper until the orange dot becomes fuzzy and faint, but is still visible.
- Have your partner use the ruler to measure the distance between the tabletop and the wax paper, and write it down.
- Without moving the wax paper, stare at a point next to the fuzzy orange dot without moving your eyes or your head. Do this for at least 10 seconds without moving your eyes or head. What do you notice about the orange dot? Does it get easier or more difficult to see it?
- Without moving the wax paper, move your eyes or your head slightly. What do you notice about the orange dot when you move your eyes or head? Does it get easier or more difficult to see it?
- Repeat the experiment with the green dot on the red paper, then the blue dot on the red paper. Measure the height of the wax paper above the dot each time. Is the height the same for each color, or for some colors can you move the wax paper higher and still see the dot?
Extra: When you get to the point in the experiment where you’re focusing on a point next to the dot, try moving the wax paper up and down without moving your eyes. Does the appearance of the dot change as you move the paper? Does it get easier to see?
Extra: When you get to the point in the experiment where you’re focusing on a point next to the dot, try sliding the colored paper (with the dot on it) side to side without moving your eyes. Does the appearance of the dot change as you move the paper? Does it get easier to see?
Extra: Repeat this experiment using different colored paper as the background. Does changing the background color change the appearance of the dot? Does it change how high you can raise the wax paper before the dot becomes hard to see?
Observations and Results
There were two things to notice in this activity. The first point you may have observed was that, when you focused on the spot next to the colored dot, the dot seemed to disappear. However, when you moved your eyes or head, the dot was visible again. The dot seemed to disappear because of how your eyes gather information about your environment. In this experiment, the edges of the dot were blurred by the wax paper. This made it difficult for your eyes to use saccades to tell the difference between a point on the dot, and a point right next to it. Because you were staring at the same place, your eyes weren’t receiving any new information and the dot gradually faded into the background.
The second thing to notice in this activity was that you may have been able to raise the wax paper higher off the tabletop for some colors, and still see the colored dot. This is because some of the colors (like orange and red) are closer to each other in the color spectrum. This makes them more difficult to distinguish when the edges of the dot are blurred. Colors like orange and blue are farther away from each other in the color spectrum, and therefore when you put a blue dot on the orange paper, you could probably see it more clearly as you raised the wax paper.
Ask an Expert
- Now You See It, Now you Don’t! Test your Peripheral Vision, from Science Buddies
- Apparent Motion & Animation, from Science Buddies