Turning Rings
Two rings of small squares. Keep your eyes on the centre and move the picture in and out.
How to play
Look first, then answer
Two rings of small squares. Keep your eyes on the centre and move the picture in and out.
- Under a minute · one question · then the explanation
How it works — best read after you have tried it
Growing becomes turning
Nothing rotates; the picture only grows and shrinks. As it grows, every square moves straight outwards from the centre, but each one’s dark and light edges are tilted, and the cells that detect motion at such an edge can only tell how it moves across its own direction. Their tilted answers, added up around a ring, make a turn.
Baingio Pinna and Gavin Brelstaff described it in 2000. The two rings are tilted and shaded opposite ways, so their turns go opposite ways too. It also works with the phone held in your hand, moving your head in and out.