Rats fooled by optical illusion may shed light on evolution of the eye

An optical illusion that plays with our perception of brightness also seems to work on rats, suggesting that the connection between perception and pupil size evolved early on in mammals.

The Asahi illusion is made up of a series of petal-like shapes surrounding a white centre. The petals are yellow close to the centre, transitioning to black at the edges, and this gradient, combined with the shape of the petals, makes it seem as if the white centre is brighter than it actually is. …