Monkeys miss magic finger trick

“Magic” is not a term you’ll find in many science papers. But, strange as it sounds, scientists at the University of Cambridge have been using magic in their experiments for some time now. That’s because classic sleight-of-hand tricks and illusions - the staples of any conjurer - are a good way to find blind spots and roadblocks in the thinking processes of different species of animals. In experiments with birds, Nicky Clayton realised that while the jays she works with were taken in by some tricks, they were not fooled when a magician used their fingers and thumbs to try and conceal the location of a hidden treat. Intrigued by this, she and her team decided to show the same tricks to primates, which do have fingers and thumbs, to see if they would fall for the same illusion. And so they did. In order to be fooled, they think, an animal needs to have the same anatomy as the magician, as she explained to me…

Nicky - If you distill magic down to the basics. It's about having an ability to see, remember what you think you saw, and have an expectation in the future. And that's the tools that allow the magician to violate your prediction of what you think has happened.

James - What sort of trick is a good vessel for what you are trying to study here? How do you subvert the animal's expectations like you would a human's? What tricks are in your arsenal?

Nicky -
Well, you can either use cups like the famous cup and ball trick. Or the magician can use his or her hands, choreography if you like, to make you think that the object is in one place when in fact it's in a completely different hand. So one of the most famous sleight of hand tricks is called the 'French drop', and that's one in which an object appears to vanish when a spectator assumes it's been taken from one hand by the hidden thumb of the other hand.

James - How was it that birds reacted to being shown this trick? Are they, what I suppose you're trying to ascertain is whether they're able to be tricked in a counterintuitive sort of way.

Nicky - You are absolutely right, James. So we did a number of sleight of hand effects, one of which was the French drop. And we found that the jays were fooled by some sleight of hand trick, but they weren't fooled by the French drop. And that's interesting because one of the fundamental things about the way in which the French drop works is that you use your fingers and thumbs. So a key component of the illusion is that instead of performing a normal grabbing motion of the object, the thumb allows the object to fall to the opposite hand, while simultaneously pretending that an object has been pinched between the thumb, the index finger, and the middle finger. The French drop depends on having an understanding of fingers and thumbs. So when a hand works like a wing, the jays are completely fooled, just like people are. But with a French drop, they're just not fooled. They don't have an expectation of what thumbs and fingers do. And that's actually what led us to look at monkeys.

James - I can see where this is going. Yeah. Move this to an animal where they do have thumbs and perfectly, you've got the control already there in the other species which don't have opposable thumbs.

Nicky - That's correct. That's exactly what we did. Essentially playing with the animals, aren't we? And the monkeys and the zoo trainers absolutely loved watching Elias Garcia-Pelegrin, the first author on the study, perform these effects.

James - And what were the findings?

Nicky - Well, the core thing was that the marmosets that don't have opposable thumbs behaved like the jays. So they weren't taken in by the effect. But the monkeys that did have opposable thumbs, so the capuchins that have proper opposable thumbs and the squirrel monkeys that have semi opposable thumbs were completely fooled by the effect, just as humans are.

James - It's so interesting, this idea that you need the physical anatomy yourself to be fooled by this trick. You must have been, or the whole team must have been very encouraged by these results.

Nicky - Completely different bits of your body shape other bits of your body. Who would've thought that your hands would have control of what you think you saw and remembered. Surely that's the job of the eyes and the brain, and yet it's all interrelated. You know, there's some lovely Jacob Bronowski quote, the hand is the maker of the mind. And this I think is a lovely example of just that.

James - Well, I'm sure he didn't have an idea how right he was <laugh>.

Nicky - Exactly. He'd be very happy right now, wouldn't he?