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Your eyes are placed where they are for a reason. This experiment shows why.Sebastian Willnow

Let’s Talk Science and the Royal Society of Canada have partnered to provide Globe and Mail readers with relevant coverage about issues that affect us all – from education to the impact of leading-edge scientific discoveries. Let’s Talk Science offers a number of fun activities to get youth engaged in STEM.

Ever wondered why we have two eyes (and not one, three or more)? Find out how your two eyes work together in this hands-on activity.

What You Need

  • Piece of paper
  • Pencil
  • Table
  • Chair

What to Do

  1. Make a small dot on a piece of paper and place the paper on a table.
  2. Sit in a chair about an arm’s length away from the paper and close one eye.
  3. Hold a pencil in your hand and hold your arm straight up.
  4. Bring your arm down slowly and try to touch the tip of the pencil to the dot. How close did you get on the first try? Did you aim too close or too far? How many tries did it take to touch the dot?

What’s happening?

Your eyes are placed where they are for a reason — they give you depth perception. That means your eyes can “see” (or “perceive”) the distance of an object. If you couldn’t see something with both eyes at the same time, it would be harder for your brain to perceive the distances between you and the object. Your brain needs to receive a different “picture” from each eye to give you depth perception.

Why does it matter?

Depth perception helps us move and function in our world. It helps us see how far or near something might be, like a moving car or a ball that is thrown towards us. Depth perception can help keep us safe when riding our bikes or driving a car because these tasks require us to judge distances and maneuver around objects and obstacles. When humans relied on hunting for survival, binocular depth perception was necessary to see how far an animal was in the distance so that they could aim an arrow or a spear. Most predators in the animal kingdom have two eyes on the front of their heads, providing them with the depth perception to successfully jump or pounce on their prey.

Investigate further

  • Try closing the other eye. Did your pencil land in the same place? Were you more successful with your right or left eye?
  • Try to do it with both eyes open. What happened? Why do you think this happened?

Discover more free, English and French, Let’s Talk Science hands-on STEM activities, resources and events online.