Figure 1.

SFM cylinders were constructed from two transparent sheets of random dots moving in opposite directions. When dots were at the same depth (binocular disparity=0), the direction of rotation was bistable. Binocular disparities applied to the left- and rightward moving dots disambiguate the direction of cylinder rotation: putting the leftwards moving dots in front and the rightwards moving dots at the back yields a clockwise rotating cylinder (as viewed from above). CW, clockwise; CCW, counter clockwise. Reprinted with permission from Parker & Krug (2003, p. 434). Copyright © Elsevier.