For this activity, you will need two curved cards. You can either print out an image of them, then cut it out or use a compass, pencil and ruler to make the image yourself.
If you have a printer
To make two cards using a compass, ruler and pencil
Once you have your cards
You should find that when you hold the cards with the curves facing the same way, one will look larger than the other. Like many optical illusions, this effect depends on how our brain interprets the information it receives from our eyes.
Our brain has as much to do with how we see things as our eyes. Our eyes receive light, but there is a large part of our brain, called the occipital lobe, responsible for analysing the signals from our eyes and constructing an image of the world around us.
The way our brains try to work out which card is larger is by looking at the sides where they are close together. Since the long side of one card is next to the short side of the other, our brains interpret that as meaning that card is larger than the other, even though we know they are the same size.
When we hold the cards so the sides that are next to each other are the same length, we can see that the cards are the same size.
During the first few years of our lives, our brains gradually learns to understand what our eyes are seeing, such as judging distances or how large objects are. Although the methods our brains use are pretty effective, there are times when they can produce false results, such as this optical illusion.
Seeing how our brains can be fooled by optical illusions help us to understand how our brains process the signals from our eyes. This particular illusion is one of my favourites because it is so simple there are no complicated lines or patterns that you often find in optical illusion. I also like it because you have a physical object you can move around, rather than just images on a page.
|Editor: Justin McGuire||