Stare at the centre of the wheel and then look away, can you catch the wheel moving?
The wheel appears to move even though in reality it is completely stationary. This visual illusion can be so strong that after looking at it for a few moments many people begin to feel nauseous.
Notice that the wheel only seems to move while in your peripheral vision, when you look directly at the wheel you can’t ‘catch’ it moving.
The wheel is made up of four coloured elements: black, purple, white and green – in that order. The critical feature for making the wheel rotate is the difference in the levels of luminance (light) between each of the elements. This means the illusion can work when printed in black and white as well.
What’s happening in your brain?
For many years scientists have known we have specific cells in our brains that fire when we look at something moving in a particular direction. These cells are called direction-selective neurons. When scientists examined this illusion they found something quite remarkable.
Direction-selective neurons begin firing when looking at this illusion. This is particularly exciting because up until now, scientists thought this type of brain neuron could only be activated by seeing something that was really moving (either on-screen or in the real world).
Vision scientists think the cells that detect motion actually interpret the rollers as if they were really moving. There is still so much unknown about the brain and visual illusions give us a new way to look at things.