By Rachael Buchanan
Magicians have been using a clever mix of dexterity and deception for centuries to astound and captivate their audiences.
Prof Wiseman calls magic a "social contract for disaster"
But how do they fool people who know they are going to be duped?
Well, cutting edge-psychology is now being applied to this most ancient of entertainment forms, to understand how these masters of legerdemain trick the complexities of the human brain.
The techniques involved have been discussed this week at the Science Museum's Dana Centre, being held to mark the centenary of the Magic Circle.
At the vanguard of this unusual appliance of science is University of Hertfordshire psychologist Professor Richard Wiseman.
As a former conjurer, he is uniquely qualified to understand the social dynamics between a magician and his audience and he argues that there is a lot more happening in a magic show than people realise.
"The really good performers," he said, "the ones who know what they're doing, have an incredible grasp of psychology", and use it to convince you to see their version of events.
One, two, three
Many of their mind tricks of the trade are surprisingly simple and boil down to misdirection - of gaze, attention, suspicion or even memory.
Body language is key. An audience can be misled about the location of an object by tensing or relaxing hands to make them look full or empty.
Another important social cue is direction of gaze and head movement. If a performer looks in a particular direction, the natural reaction is to follow, giving him a brief window to make his move.
It is vital that when the audience realises they have been had, they cannot properly recall the fine details in the series of events which led up to the effect, and so deconstruct it.
"For example," said Professor Wiseman, "a magician might cut some cards and say 'Right, they're mixed up now'. Then he'll do something else and then say 'Now, remember I shuffled the cards at the start'.
"That word - 'shuffled' - has gone in, and people think 'Yeah, that's right, the cards were shuffled'. But they weren't, he just cut them. It's cut to mix to shuffle. Small steps. If you had gone from cut to shuffle, it's too much and people notice."
And magicians are not the only ones playing tricks; your mind is at it, too.
"People think the way their perception works is simple," said University College London neuroscientist Geraint Rees. "They think it's like having a viewing room inside their brain with a little man sitting there monitoring a big bank of video feeds from outside, but it's not so straight forward."
Vision is not the only sensory data the brain receives at any one time.
Every moment, the mind is bombarded with a cacophony of sights, sounds, smells, tastes and physical sensations. Your consciousness has to continually meld all this data together and make sense of it.
So it takes a few shortcuts and unless a major change occurs to grab your attention, your brain will not refresh the scene. In short, you see what you expect to see - and that is very helpful to an illusionist.
Just like that: Look at my hands
Scientists have devised a myriad of weird and wonderful ways to test this - to show how much people miss right in front of their eyes.
US scientists Daniel Simons and Christopher Chabris are keen students of what is called "inattention blindness".
They have a test which involves showing subjects a video of two basketball teams, one wearing white and the other black. Subjects are told to count the passes between the white team and most become so focused, they fail to notice a woman walk across the court with an umbrella.
"We have a limited processing capacity and can only perceive what we attend to," said UCL psychologist Dr Nilli Lavie.
"If the information we are paying attention to is taking all of our capacity, it doesn't leave capacity to perceive anything else."
On the spot
Dr Lavie specialises in inattention blindness. "The skill of a good magician is to make a very interesting, dramatic act with complex actions and interesting verbal utterances," she said.
"He loads your attention with all this information, but it's irrelevant to the act that he presents. It is so you don't notice the deception."
However, humans being natural sceptics go to magic shows knowing they are going to be deceived so they pay special attention to everything. But being overly focused can also be turned to the illusionist's advantage.
Dr Lavie asked a couple of thousand people at the Science Museum in London to help her in a study.
They were told to spot whether an "X" or an "N" appeared within a briefly displayed ring of random letters.
They were also told to expect the occasional brief appearances of a small circle. They were even shown the circle, yet most failed to see it because their attention was overly focused on the letters.
She sees parallels with magic shows. "With magic you expect something is going to happen but you still don't see it because your attention is being otherwise engaged."
Who's a sucker?
To test this theory, Durham University psychologist Gustav Kuhn employed an eye-tracking device to monitor exactly where people look when watching magic.
In his trick, a cigarette vanishes simply by being dropped. He found that even when viewers were told that the cigarette would disappear, the majority still missed the method.
"It doesn't depend on where you look," he said. "The most important fact is what you are attending to. People can look straight at the cigarette and not see it drop."
Magic reaches into the hat for something childlike
So what motivates people to let magicians mess with their minds. After all, there is a fundamental problem with this relationship. At the end of the day, you are paying someone, to deceive you; you are twice the sucker.
Professor Wiseman calls it a "social contract for disaster".
"I show you a trick, you want to know how it's done, I am not going to tell you. Conflict."
'Kings of cool'
Magicians have to manage that. And to do that they use these psychological techniques, but they are also giving something back.
In a renowned essay, Paul Harris, one of David Blaine's technical advisers, has argued it is "astonishment". This, he claims, is our natural state of mind; analogous to a childlike awe, that is lost in adulthood. Good magic, Harris claims, returns people to that state.
Today, it is the edgier performers like Derren Brown and David Blaine that people want to see.
They are both charged with wresting magic back from the grip of the likes of David Copperfield, Paul Daniels and Lance Burton - the poster boys for high-camp family entertainment.
Yes, Blaine and Brown will astonish, but they will also unsettle; they take you on a journey to the parts of your childhood inhabited by the scary clown, not Peter Pan and the fairies.
Today's popular performers have re-invented the art
In reality, their tricks are the same as those played out over generations. Blaine's genius was to strip out the outdated paraphernalia of corny catch-phrases, tuxedos and Vegas-scale stunts and work on the effect instead.
His TV show was successful because it was street magic with the safety catch off.
He sprang his tricks on unsuspecting passers-by, and then lingered on their reaction, focussing more on their discomfort at what they had experienced than the trick itself.
Transporting modern cynical audiences back to a childlike state of wonder is a tall order even for these kings of cool. But Wiseman believes Derren Brown is doubly astute, using people's natural scepticism and demand for answers to his advantage.
"If he passed himself off as having psychic abilities, he wouldn't be half as successful," Professor Wiseman insists.
Instead, Brown offers a rational explanation dressed up in science to explain the tricks he does. He presents himself as having amazing powers of memory and psychological manipulation and so offers the audience a "believable" solution, albeit often the wrong one.
"Derren's trick is not the magic, it's creating the illusion that he has these fantastic abilities and getting you to believe him."