A Shrink and Swell Illusion

We  just got into the final top ten entries in the annual Best Visual Illusion of the Year contest.  We didn’t get in the top three, (in fact, we seem to have come last … ) but it’s great to have made the top ten.  The movie here is a different version of our competition entry.

The illusion is that the objectively static sides of a V-shaped window appear either to expand or to contract horizontally. Figures within the window, expanded at the top and squashed at the bottom into the V-shape, rise or fall at constant speed.  In the middle section of the movie, with coloured figures, you can see that the moving bacground around the V-shapes is not essential, the illusion is still there without it, maybe reduced.  You can also see that with figures that just rise, without the squeeze and squash, there’s no illusion.

At the end of this version, we show that we’ve actually found three fairly different ways of producing this illusion.  We found them by studying the reflections seen in novelty illusion rings called Witch Rings as they rotate.  We posted about using animations to imitate effects seen in the reflections, in 2013, and then in 2015 and 2016.  But now we think the illusion we’ve found in our animations, though an interesting discovery, only makes a small contribution to the very vivid illusion seen in the rings in the real world – the secret of the rings remains mysterious!

I’ll post with some more demonstrations of what we think may be going on in the illusion in a few days.