Hidden colours

HOW

1. Look at the pattern on the stationary disc.
2. Rotate the disc at high speed. You can see faint, unsaturated, coloured rings on the disc.
3. Talk to another person. Check whether you see the same colours.

WHY

The so-called cone cells are responsible for colour vision. These are light-sensitive nerve cells that are located on the retina. There are three types of cone cells depending on the colour they respond to: red, green and blue. The other colours are produced by activating different numbers of primary cone cells. The colour black does not stimulate any cone cells, while all three respond to white.

It is assumed that the response time of the different types of cone cells varies. Switching from the reception of white to black, these nerve cells send black colour information to the brain at different times. It therefore interprets the image as containing other colours. For example, the blue cone cells, which are late during signal switch-off, will signal the existence of that colour, even though it is no longer there.