The peripheral drift illusion (aka PDI) is a motion illusion generated by the presentation of a sawtooth luminance grating in the visual periphery.
This illusion was first discovered Jocelyn Faubert, a psychophysicist best known for his work in the fields of visual perception, and Herbert in 1999, although a similar effect called the "Escalator Illusion" was reported by Fraser and Wilcox in 1979.
A variant of the PDI was created by Kitaoka Akiyoshi and Ashida in 2003, who took the continuous sawtooth luminance change, and reversed the intermediate greys. Kitaoka has created numerous variants of the PDI, and one called "rotating snakes," which became very popular.
The illusion is easily seen when fixating off to the side, and then blinking as fast as possible. Most observers see the illusion easily when reading text with the illusion figure in the periphery. Motion is consistently perceived in a dark-to-light direction, so the two circles to the right should spin in opposite directions.