Chimps, other apes take mind reading to humanlike level

Eye-tracking data shows animals can anticipate a person’s thoughts, actions


MIND READER  A group of captive apes, including this orangutan, performed tests indicating that they can grasp when others are about to act based on false beliefs. This finding indicates that social thinking skills of apes and humans are more alike than previously thought.


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Apes understand what others believe to be true. What’s more, they realize that those beliefs can be wrong, researchers say. To make this discovery, researchers devised experiments involving a concealed, gorilla-suited person or a squirreled-away rock that had been moved from their original hiding places — something the apes knew, but a person looking for King Kong or the stone didn’t.

“Apes anticipated that an individual would search for an object where he last saw it, even though the apes knew that the object was no longer there,” says evolutionary anthropologist Christopher Krupenye.

If this first-of-its-kind finding holds up, it means that chimpanzees, bonobos and orangutans can understand that others’ actions sometimes reflect mistaken assumptions about reality. Apes’ grasp of others’ false beliefs roughly equals that of human 2-year-olds tested in much the same way, say Krupenye of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, and his colleagues. 

Considering their targeted gazes during brief experiments, apes must rapidly assess others’ beliefs about the world in wild and captive communities, the researchers propose in the October 7 Science. Understanding the concept of false beliefs helps wild and captive chimps deceive their comrades, such as hiding food from those who don’t share, Krupenye suggests.

Experiments included 41 apes — 19 chimps, 15 bonobos and seven orangutans. These animals had been born in captivity and lived in open enclosures at research centers in Germany and Japan. Apes watched two short videos designed to grab their attention. In one, a person in a King Kong gorilla suit hides in one of two haystacks while a man watches. After the man leaves through a door, King Kong runs away. Then the man returns and looks for King Kong. In a second video, a man returns for a stone that King Kong stole from him and hid in one of two boxes while the man watched. During the man’s absence, however, King Kong runs off with the stone or, in another version, moves the stone from one box to the other.

A camera equipped with an eye-tracking sensor revealed that, when the man in these videos returned, apes usually looked first at where King Kong or the stone had initially been hidden. They also spent more time looking at those initial locations than at any other spots in the videos. Those behaviors indicate that the apes assumed the man would return to those same spots based on where he had last seen what he was looking for. Of 29 animals that viewed both videos, gazes of 23 indicated that they expected the man in one or both scenarios to hold a false belief, the researchers say.

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DECEPTIVE LOOKS In three trials from a new study, apes are shown at upper left watching trials in which an experimenter wearing a gorilla outfit steals a stone from a person behind a mesh screen and then hides the stone under one of two boxes or runs away with it. Red circles denote where each ape is looking during experiments. Looking patterns indicate to researchers that the apes understood when the person held false beliefs about where to find the stone. C. Krupenye, Fumihiro Kana, MPI-EVA, Kumamoto Sanctuary

Krupenye’s team shows for the first time that a nonhuman animal can track others’ false beliefs, agrees psychologist Amanda Seed of the University of St. Andrews in Fife, Scotland. But it has yet to be demonstrated that apes, like humans, can act on such knowledge, say by hiding food from others, she adds. It’s also unclear whether, aside from knowing where an observer will look for an item, apes truly know that the object is no longer there, Seed says. Further experiments could see if apes express surprise upon seeing an observer find an item hidden in its original location after it had been moved, she suggests.

An ability to infer what others are thinking, dubbed “theory of mind” by psychologists (SN Online: 3/27/13), likely evolved in ancient ancestors of humans and apes, writes primatologist Frans de Waal of Emory University in Atlanta in the same issue of Science. Those ancestors lived in increasingly complex communities where it paid to predict accurately how others would behave, he proposes.

Yale University psychologist Laurie Santos isn’t so sure apes track false beliefs. Previous research has consistently indicated that no nonhuman animals monitor others’ beliefs, even on tasks similar to those used by Krupenye’s team, Santos says. In the new study, she adds, apes may have realized that an observer was ignorant about an object’s new location but not that he had false expectations about where to find it.

Krupenye disagrees. “The apes specifically anticipated that the actor in the video would search for an object where we humans know the actor falsely believed the object to be,” he says.

Bruce Bower has written about the behavioral sciences for Science News since 1984. He writes about psychology, anthropology, archaeology and mental health issues.

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