The psychology of magic

03 November 2014

Interview with

Gustav Kuhn, Goldsmiths University of London

Magic shows are hugely popular, but just how do magicians make us fall for tricks, over and over again? Gustav Kuhn, from Goldsmiths University of London, is a psychologist working on attention, and also a magician. He showed Chris Smith, Magician Ginny Smith and the live audiences the secrets behind a couple of his tricks, and explain what they can tell us about how the brain works. 

Gustav -  I started off as a magician and my interest in magic really led me to study psychology and now, I study the science of magic.

Ginny -  If we look at science, are we going to ruin the fun of magic?

Gustav -  Well, I don't think so.  I mean, magic is very interesting in that magicians have developed really very powerful techniques to manipulate your perception.  By studying some of these techniques, we can actually work out quite a lot about how the brain works.

Ginny -  Can you show us a trick then?

Gustav -  Yeah.  I will show you a couple of tricks.

Ginny -  Okay, so I'm going to try and describe what you're doing for our radio audience.  So, you've got a Ping-Pong ball and you're throwing it up and down in one hand and it's gone.  You threw it up and I saw you catch it again, then you threw it again and I saw you catch it again then you threw it again and it disappeared.

Gustav -  So, this is known as the vanishing ball illusion.  It's actually is very, very simple.  How many of you saw a ball move up in the last throw?

Ginny -  That's at least a third of the audience think they saw it going up.

Gustav -  So about a third of the audience.  So, what's happening here is I've got a ball and I throw it up in the air a couple of times and on the final throw, I just pretend to throw it up, but in fact, it's actually held inside my hand.  Now, what's very interesting about this illusion is that most people actually experience a ball moving up and then disappearing somewhere sort of like between me and the ceiling even though the ball hasn't actually left my hand.

Ginny -  We're getting lots of nods from the audience, people who definitely thought they'd seen that ball.

Gustav -  And so, this is a really nice example to demonstrate that really what you're seeing is not necessarily the way the world is, but it's much more related to the way that you expect the world to be.  So because you're expecting the ball to be kind of like leaving the hand, that's why you actually experience the ball sort of like moving up.

Ginny -  And it is what you were doing with your hand and the fact that you actually followed it with your eyes, is that important as well?

Gustav -  Yes, so in magic, social cues are very important, so where I'm looking.  So, if I do the same illusion again, but this time, I'm just looking at the hand that's holding the ball, well the effectiveness of the illusion is really reduced.  What this shows us is that our brain is automatically picking up cues to predict what the world is going to be like in the future.  I can show you another example that sort of like highlights the importance of these social cues as well.

Ginny -  Who wants to see another trick?

Audience -  Me!

Ginny -  I think they'd like to see another one.

Gustav -  So, this is again is a very simple trick.  I've got a green lighter here on the table.

Ginny -  There's a green lighter on the table.  You're lighting it and clicked your fingers...oh, it's gone.  So, it was in your left hand.  You lit it.  You waved your right hand over the top of it then you opened your right hand.  It definitely wasn't in your right hand.  But then you also opened your left hand and it wasn't in that hand either.  Is that what everyone else saw?

Gustav -  So, can we just have a show of hands of how many of you saw how the lighter disappeared?

Ginny -  We've got a few hands.  What did you think?

Male -  I saw him dropping it.

Chris -  Gustav, you've been caught out.  You dropped it apparently.

Gustav -  I'll do exactly the same thing again.

Ginny -  Right.  So, you've lit the lighter, you waved your right hand and clicked, you've - oh, it's on your lap!

Gustav -  Now, how many of you saw how the lighter disappeared?

Ginny -  Okay, most of you saw it that time.

Gustav -  Yes, so the lighter was really just dropped.  This is not actually a real magic trick.  I'm kind of using misdirection to sort of demonstrate really how little of the environment that you're normally aware of.  So, what's happening is I'm picking up the lighter, I light it so we got a bright flame, and this flame will actually capture your attention.  I then pretend to take the flame with my hand and I'm using my social cues.  So, I'm using my gaze to distract your attention and move your attention from the lighter to my other hand.

Ginny -  So, we're all watching your right hand which you've been waving around over the flame and you've brought away from it.  So, we stopped looking at your left hand, the one that had the lighter in.

Gustav -  Yes.  So, no one's attending to the left hand holding the lighter.  I'm looking at the other hand, I'm snapping my fingers so you can hear a sound.  I'm moving it, hopefully, misdirecting your attention and therefore, preventing you from seeing the lighter drop.  One of the remarkable things about visual perception is that I'm kind of looking out here in this audience and I feel like I'm aware of most of the things that are actually going on around me.  Yet in actual fact, once we start probing our visual awareness, we realise that you're actually only aware of a really very small fraction of the information.  So, although you think you'd see things, in actual fact, most of the time, unless you're actually attending to them, you don't necessarily see them.  In a lot of our research, we use eye tracking that allows us to measure exactly where people are looking.  What's really remarkable there is that people can actually be looking at the lighter and yet, they still don't see it.  And of course, intuitively, you think that surely, if I'm looking at something, I should be able to see it.  But what a lot of these research is really telling us is that if your attention is being distracted, you just won't see it even if it's really right in front of your eyes.

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