Two rotating cylinders are placed left and right, like wheels joined by an invisible axle. As you watch, you might notice they often appear to rotate together in the same direction, synchronously switching direction every few seconds, like wheels rolling towards and you then away.

Only the right cylinder is physically reversing direction. The impression that the left cylinder is switching at the same time is illusory, because in reality the dots keep going the same way. So objective switches on the right trigger subjective switches on the left, as if by remote control.

This illusion demonstrates how we use disambiguating contextual information to make sense of confusing stimuli. Intriguingly, this ‘remote-control’ illusion fails when the ‘axle’ between the cylinders is broken (by arranging each cylinder so their open ends are no longer aligned), as if reflecting the behaviour of objects in the physical world (Vision Research, 2006

).