Kitaoka-and-Pinna Christmas Illusion
Copyright © Ben Backus 2011

This image combines twomotion illusions: Akiyoshi Kitaoka’s
Rotating Snakes illusion, in which a stationary pattern appears
to move as you fixate one part of the image after another, and
Baingio Pinna's rotating rings illusion, in which concentric rings
appear to counter-rotate as you move your head towards and
away from the image. Both of these illusions use repeated asym-
metric patterns to trigger the visual system's "local motion" de-
tectors.   These small, localized illusory local motions are then
combined across the entire ring by a "global motion" detector
whose job it is to detect such patterns within the visual field.

More info:

Robert Krulwich, NPR blog, “This can’t be happening” (9 Aug 2011)
(describes how Pinna's illusion works)

Backus, BT and Oruc, I (2005). Illusory motion from change over time in the
response to contrast and luminance. Journal of Vision, 5, 1055–1069.
(describes how Kitaoka's illusion works)