Lilac Chaser

The lilac chaser is a visual illusion consisting of twelve blurred lilac-colored discs arranged in a circle, which disappear one after another in clockwise sequence, each vanishing and reappearing so that a single gap appears to travel steadily around the ring. A viewer who stares at a small cross fixed at the center of the circle for about thirty seconds typically experiences the illusion unfold in three stages: first a gap moving around the circle, then a green disc that appears in place of the gap, and finally the perception that the green disc itself is moving around the ring against the background while the lilac discs themselves seem to vanish entirely. The illusion combines three separate, previously known perceptual effects: the phi phenomenon, in which rapidly displayed separate objects are perceived as continuous motion; the afterimage effect, in which the complementary color green appears once a lilac stimulus disappears, caused by neural adaptation in the retina's own color-sensitive cells; and Troxler's fading, in which a blurred, unmoving stimulus disappears from conscious perception even though it remains physically present in the visual field. Jeremy Hinton created the lilac chaser before 2005 while developing experiments on visual motion, refining the illusion by adjusting the discs' color, number and timing, and the vision scientist Michael Bach later popularized the illusion online by hosting an animated version of it under the name Lilac Chaser, after which it became widely known on the internet around 2005.