Focus on the plus in the middle. the purple dots should dissapear.
Amazing Eh?
Lilac chaser is a visual illusion, also known as the Pac-Man illusion. It consists of 12 lilac (or pink or magenta-like), blurred disks arranged in a circle (like the numbers on a clock), around a small, black, central cross on a grey background. One of the disks disappears briefly (for about 0.1 second), then the next (about 0.125 second later), and the next, and so on, in a clockwise direction. When one stares at the cross for about 20 seconds or so, one first sees a gap running around the circle of lilac disks, then a green disk running around the circle of lilac disks, then a green disk running around on the grey background, the lilac disks appearing to have disappeared or to have been erased by the green disk.
Amazing Eh?