Pulling a rabbit out of your brain

Can magicians teach us anything about psychology? Marcus Pearce looks at the evidence ... and shows off some neat tricks

Someone once quipped that while a magician pulls rabbits out of hats, an experimental psychologist pulls habits out of rats. It seems times have changed as scientists are now investigating the psychological principles behind magic tricks.

In a paper published this month in Trends in Cognitive Sciences, Gustav Kuhn, Alym Amlani and Ronald Rensink argue that age-old tricks used by magicians can be useful in studying human perception and cognition. They say that magicians, like scientists, have theories about perception that can be proved wrong if the audience spots the secret, although Kuhn, himself a practising magician, claimed that, "Magicians are in some ways miles ahead of scientists."

But can magic tricks really contribute to psychology? And if so, how? Let's look at some examples from the paper which illustrate the psychological principles behind some key techniques of the magic trade: misdirection, illusion and forcing.

Misdirection involves manipulating people's attention to prevent them from seeing how the trick was done. Here's an example, taken from the paper, of a disappearing cigarette and lighter.

More than half of the 46 people tested by the researchers did not see the cigarette falling even though it is dropped in full view and, in several cases, eye movement data showed that they were looking straight at it.

In this case, there are apparently three ways in which attention is focused on the right hand holding the lighter: the surprising disappearance of the lighter, the social cues created by the magician looking at his right hand and the physical cues created by the magician moving his hand and snapping his fingers. According to Kuhn, these effects are usually studied separately by psychologists in artificial situations whereas the magician's ability to combine them correctly allows them to be studied together in a realistic context, producing greater effect sizes.

Elsewhere on the web, the colour-changing card trick is another particularly striking example of so-called change blindness. And this clip used by Becklen and Cervone (1983) in an experiment on inattentional blindness is the grandmother of a host of videos involving people in gorilla suits.

Another technique used by magicians is illusion, which relies on creating a perception based on expectation rather than reality. In the example reported, people watched a video of a magician who throws a ball in the air twice and on the third time pretends to throw it but actually conceals it in his hand. When the magician's gaze appears to follow the imaginary third ball to the ceiling, 68% of people claim to have seen the ball moving towards the top of the screen compared with 32% when he looked at his hand.

Eye-tracking data showed that they tend to glance at the magician's face so as to use "information about where the magician is looking as a way of predicting the location of the ball". These examples highlight the effects of social cues - pro-social and anti-social - which, according to Kuhn, are "largely ignored" in research on expectation in visual perception.

Finally, forcing involves manipulating people's decisions without their noticing (typically using knowledge about biases and stereotypical responses). This has not yet been studied in any great detail by psychologists, says Kuhn, but he expects that the magician's ability to induce reliably large changes in behaviour - forcing someone to choose a particular card, for example - might be useful for research on subliminal perception where the effect sizes in typical experiments (eg effects of words presented too quickly to enter consciousness) are usually very small.

Kuhn and his colleagues emphasise that they carefully design their procedures so as not to reveal how particular magic tricks work.