Best illusion of 2012: The disappearing hand trick

Catherine de Lange, contributor

Think you would know if your own hand disappeared? A new illusion developed by psychologist Roger Newport and his team at Nottingham University in the UK shows how people can be fooled using a simple but clever trick - clever enough that yesterday it was awarded first prize in the 2012 Best Illusion of the Year Contest.

Over 10 years ago, researchers discovered that it was possible to make someone think that a rubber hand is their own by combining the senses of tough and sight. This led Newport's team to wonder whether the opposite could also be true. Could they separate the senses to make somebody feel like their limb had disappeared?

They came up with a device called a MIRAGE multi-sensory illusion box where a volunteer places their hands under a screen which projects the image of their hands in-between two blue lines. During the experiment, the lines move inwards and all the volunteer has to do is try to make sure the blue lines don't touch their hands.

What the volunteer doesn't realise is that the screen isn't projecting exactly what's going on underneath. In order to dodge the blue lines, the volunteer will gradually move their hands outwards but the hands on the screen look fixed in place. After just 25 seconds, the volunteer has moved their hands much farther apart than they think.

Eventually, one of the hands on the screen disappears. Of course, the volunteer doesn't really believe their hand has vanished until they reach across to feel it and become aware of the trick. The illusion is designed to simulate the loss of awareness experienced after a stroke.

Journal reference: Current Biology, DOI: 10.1016/j.cub.2011.08.044

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