Chimp’s gift for numbers

Translating numbers into colors may explain an animal’s apparent memory trick

Ayumu the chimpanzee plays a number memory game faster and more accurately than any human player.  T. Matsuzawa, Primate Research Institute

Whatever you do, don’t challenge a chimpanzee named Ayumu to a number memory game.

In 2007, Ayumu became famous for his lightning speed at a game that goes like this: A player views a computer screen where the numbers 1 through 9 appear briefly at once. Then they turn to white squares. The player then taps the squares where the numbers had been, in order from 1 to 9. People can do it. But no human competitor has ever completed the game faster or more accurately than Ayumu.

Fast-forward five years: Ayumu remains undefeated.

Psychologist Nicholas Humphrey works at Darwin College at Cambridge University in England. He thinks he now knows the secret behind the chimp’s ability. Humphrey suspects Ayumu’s brain may have a condition that allows the chimp to see numbers as colors. This would mean that Ayumu may see a color glow after the number vanishes. Then, instead of remembering the numbers, he remembers a sequence of colors, each associated with a number.

“When you get extraordinary results, you need to look for extraordinary ideas to explain them,” Humphrey told Science News. 

The condition that Humphrey believes Ayumu may have is called synesthesia. Humans with synesthesia may associate numbers and letters with colors. For example, a person may see the number “5” as the color blue. Every time. Until now, scientists had assumed only humans could have synesthesia.

Humphrey found the inspiration for his idea at a 2011 scientific conference. There, he heard a presentation about Ayumu’s memory abilities and another talk about synesthesia. He then put the two ideas together.

Not everyone is convinced Humphrey is right. Primatologist Tetsuro Matsuzawa works at the Primate Research Institute at Japan’s Kyoto University. He has spent decades studying the amazing memories of chimpanzees. These include Ayumu. He maintains that chimps simply have faster memory recall than people.

But, “I don’t deny that humans are wonderful creatures,” he told Science News.

Watch Ayumu the chimp race through a number memory game. Credit: T. Matsuzawa, Primate Research Institute

Power words

primatology The study of primates, a family of animals that includes monkeys, apes and humans.

synesthesia A brain condition in which a person connects a sense experience to an unassociated symbol, as a letter or number.

psychology The study of the human mind, especially in relation to actions and behavior.

Stephen Ornes lives in Nashville, Tenn., and his family has two rabbits, six chickens and a cat. He has written for Science News for Students since 2008 on topics including lightning, feral pigs, big bubbles and space junk.

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