Our physical attributes help us to predict the actions of others and therefore often affects our perception of what is going on and what might happen

A study with monkeys, two species of which had opposable thumbs while the third didn’t, indicated to the researchers “the intriguing possibility that an individual’s inherent physical capability heavily influences their perception, their memory of what they think they saw and their ability to predict manual movements of those around them.”

Small common squirrel monkeys (Saimiri sciureus). Notice the thumbs.
Small common squirrel monkeys (Saimiri sciureus). Notice the thumbs. Licensed image.

The study tells us that our physical attributes help us to predict the actions of others and therefore often affects our perception of what is going on and what might happen. – MikeB

The study

The researchers performed a vanishing trick and the audience was three different monkey species. It’s that well-known vanishing trick in which a coin is placed in one hand and the other hand passes over it. The coin disappears and the magician holds up their hand to show that it has gone.

The key element is that the coin is held between the tip of a finger and the thumb with the palm facing down initially. When the other hand, with the thumb curled is passed over the hand holding the coin, it is no longer visible. It is a disappearing object trick.

But as you can note, the thumb plays a role in the trick. It is part of how people perceive the trick. With monkeys as the audience, they didn’t use coins but food treats such as peanuts for the capuchin monkeys, worms for the squirrel monkeys and marshmallows for the marmosets. The marmosets do not have opposable thumbs.

Our thumbs work opposite to the fingers and therefore we can grab hold of things with them.

The results were intriguing in that:

  • In 81% of the magician’s tricks, the capuchin monkeys fell for it and thought that the treat had been taken by the second hand.
  • In 93% of the tricks the squirrel monkeys fell for it in the same way.
  • In only 6% of the tricks, the marmosets were fooled by the “magic”. They did not assume that the second hand that snatched away the coin because their perception of the trick was coloured by the fact that they don’t have thumbs and therefore didn’t understand how the thumb worked. On that basis they didn’t believe that the second had taken the coin.

Dr. Elias Garcia-Pelegrin, an assistant professor at Cambridge University where the study took place, said:

By investigating how species of primates experience magic, we can understand more about the evolutionary roots of cognitive shortcomings that leave us exposed to the cunning of magicians.

He believes that the study explains why tricks work.

And the study does tell us that our physical attributes help us to predict the actions of others and therefore often affects our perception of what is going on.

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