A trick of the heart...or eyes?

A trick of the heart...or eyes?

Is it an optical illusion?

Play the film below, or watch it on YouTube.

Stare at the + in the middle of the screen. Keep staring!

What happened to the pink dots?  What happened to the dots after they were removed?

What's happening?

Most people, if they concentrate on the cross, see the pink dots disappear. BUT, the dots don't really disappear. Instead, your eyes deceived you. It is an optical illusion.

When you concentrate on a certain point, things in your peripheral vision (outside the centre of your vision) disappear, because your brain isn't taking any notice of them anymore.

The illusion works well with pink dots on a grey background because there is a low contrast between the two colours. If it was black dots on a white background, the contrast would be higher and your brain would find it harder to ignore the black dots.

Did you see green dots when the pink dots were removed? This is called an afterimage. You have light receptors in your eyes which are sensitive to red, blue and green colours. When you stared at the pink dots for a long time, your red light receptors become "tired". They have got used to the pink colour.

When the dots disappeared, the receptors that are tired do not work as well. They only send a weak signal to your brain.

The surrounding light receptors that do not respond to the pink colour are not tired and send a strong signal to your brain. The information from all your different colour receptors isn't balanced, so you see colour "afterimages".

Curriculum information