When seeing and believing are not the same
The above circles are not moving, although they appear to be. The image comes from Clive Gifford's book Eye Benders: The Science of Seeing and Believing.
The book, with its gallery of optical tricks, has been awarded the 2014 Royal Society Young People's Book prize, which is judged by young readers.
Gifford says the motion illusion, above, was inspired by psychology professor Akiyoshi Kitaoka from the Ritsumeikan Asia Pacific University.
Gifford explains: "Most people can stop the illusion simply by concentrating upon and focusing on a single wheel in the image. The difference in luminance between different parts of the wheels and how your eyes repeatedly scan an image, a little like a twitchy digital camera continually autofocusing and adjusting the eye's lens, are believed to be responsible for creating the illusion of the wheels turning round."
See more images from Gifford's book here.