Coloured Curves

What's this Science Bite about?

The human body is jam packed with amazing organs that work together to keep us alive. The organ in charge of coordinating every single thing our body does, from singing a song to riding a bike, is the brain.

The brain is working continuously, processing the stream of information it receives to make sense of the world around you.

You actually see with your brain, not your eyes! Your perception of the world around you is dependent on how your brain interprets the images your eyes pick up. What we see is actually our brain’s translation of what it thinks is most likely to be there.

Your brain is permanently interpreting what you see and hear and the amazing thing is that it does it without you having to think about it.

What happens when our brain can’t make sense of what it is seeing?

Try our demonstration to find out.

What you'll need

A yellow and a red curve

How to do the experiment

  1. Glue the coloured curves sheet to the card and then cut out the curves. (Alternatively you can laminate them).

  2. Hold one curve above the other and ask which one is bigger?

  3. Switch the position of the curves. Which one looks bigger now?

  4. Bring the two curves together to show that they are the same size!

Find out more...

What's happening?

This is an example of an optical illusion. What your brain perceived is different from what is actually there.

This illusion was discovered in 1889, by the psychologist Joseph Jastrow and is known as the ‘Jastrow illusion’.

This is an illusion of comparison. The shorter, inner edge of the top curve is compared with the longer, outer edge of the bottom curve.

Even when you know the two curves are the same size your brain still perceives the bottom curve as being larger!

Try another illusion…

A motion illusion

This is an example of illusory motion which is also known as motion illusion. The most common type of illusory motion is apparent motion which you experience when you watch a film. The static images are displayed so quickly that you can’t perceive them individually and instead you see movement. Another example of apparent motion is electronic signs which simulate moving text by flashing lights on and off as if the text is moving.

What do you see…

An ambiguous image

This is an example of an ambiguous image. Both a rabbit and a duck are visible in this image. The rabbit is looking to the right and the duck is looking to the left.

Visit BodyWorks at Glasgow Science Centre - an interactive exhibition all about human health and wellbeing in the 21st Century.

Curriculum links

Body systems and cells

SCN 0-12a/ 2-12b



Glasgow Science Centre