Science Smarts: Two eyes are better than one

By Patty Rooks on August 9, 2025.

It is that time of the year as we all get ready to go back to school – checkups! These often include a trip to the optometrist or eye doctor. Of course, this always gets me to thinking just how do our eyes work? Well, we had better investigate this further. Let’s get started!

*Remember to ask an adult before doing this experiment.

Materials

– Cup

– Penny

– Science helper

– Measuring tape

– Masking tape

– Table

Procedure

1. Measure a distance of three metres with the measuring tape and mark it with the masking tape. Note: you may have to move the table to this location.

2. Place the cup at the mark of 3 metres on top of the table.

3. Cup one hand and place it over your eye. Make sure you cannot see out.

4. Have your partner stand at the table.

5. Have your science helper hold the penny at arm’s length above the cup, but slightly in front of it.

6. Watching only the cup and the penny, tell your science helper where to move his/her arm so that the penny will fall into the cup when s/he drops it.

7. Tell your science helper to drop the penny and see how close you came.

8. Can you tell your helper why you are such a bad shot?

What is going on?

In this experiment we were investigating depth perception. You should have learned that two eyes are definitely better than one.

Because your eyes are set apart from each other, they see everything from slightly different angles. This results in the images your brain gets from each eye are a little different from one another. By comparing the images, your brain can give you a three dimensional picture which helps you judge distances. This is called stereoscopic vision. When you cover one eye, you no longer have stereoscopic vision. And you see things in two dimensions, like a photograph. This makes judging distances much more difficult.

Fortunately, there are other clues to help you judge depth in real life, such as size, brightness and position compared to other familiar objects. These are the clues that people use if they lose the sight in one eye. You can improve your one eyed depth perception too. Try the penny test several times. You will see that it will become easier with more practice.

Mark your calendars for the praxis AGM on Wednesday, September 17, 2025 at 7:00 p.m.. We are always looking for new board members that want to share their love of science. Contact Praxis for further details.

Patty Rooks, senior scientific consultant Praxis Science Outreach Society. Praxis has moved! We are very fortunate to be located in the Community Futures Entre Corp Building at #202 556 Fourth St. SE, Medicine Hat, Alberta, T1A 0K8. For all your science needs, please email praxis@praxismh.ca.

25
-24