Three variants of illusions we have seen elsewhere on these pages. First, concentrate on the dot at the center of the image above and watch the black square expand continuously, in this example of so-called “two stroke animation.”

Next,in this blue and cream version of Prof. Michael Bach's famous magenta and neutral grey “Lilac Chaser” illusion, fix your attention on the central plus and watch the vanishing blue dots be replaced by dots of contrasting color, and finally by a continuous ring of that color. Do you understand why the illusory color is different from that seen in Bach's original version?

This is an anaglyph, which can be viewed with red-cyan stereo glasses, but even without the glasses just stare at the Christmas tree and note that it discontinuously jumps from clockwise-from-above to counterclockwise-from-above rotation. Can you shift the apparent rotation by an act of will, or does it jump back and forth uncontrollably and unpredictably?