How you see the world may be very different than how someone else sees it. And recognizing that has long been thought to be a uniquely human ability.
But when it comes to understanding others' perspectives, humans might not be alone.
"Reading others' minds is not our special skill," says Fumihiro Kano, a comparative psychologist at Kyoto University in Japan.
Nonhuman apes can do it, too, according to Dr. Kano's research, published Thursday in the journal Science, a finding that could further blur the line between the cognitive capacities of humans and nonhuman apes.
"This is surely a landmark study," Cameron Buckner, a cognitive scientist at the University of Houston who was not part of the study, writes in an email to The Christian Science Monitor. Although other animals have been found to be able to perceive others' mental states, this study is the first to suggest nonhuman animals can understand when others have a perspective that does not match reality, in other words a false belief.
"Theory of mind – the ability to infer others' mental states, such as desires and beliefs, is at the heart of so many human social behaviors, such as our unique forms of communication, cooperation, and culture," Christopher Krupenye, a comparative psychologist at the Max Planck Institute for Evolutionary Anthropology who led the study along with Kano, writes in an email to the Monitor. As such, he explains, researchers have long been fascinated as to whether nonhuman animals possess theory of mind as well.
Some research has suggested that great apes can understand some mental states, such as goals and intentions, of others. But whether they can understand when others' perspectives do not match their own perceived reality, remained an important question.
"False-belief is of particular interest because one should understand that the others' mind is driven not by reality but by beliefs about reality, even when those beliefs are false," explains Kano in an email to the Monitor. So if nonhuman apes can understand when someone has a misleading perspective, this could strengthen proof that the animals, too, possess theory of mind.
Dr. Krupenye and Kano tested three species of apes for false-belief understanding – chimpanzees, bonobos, and orangutans. The test subjects were shown videos and the researchers tracked where the animals looked while watching the movie as a way to assess what they predicted would happen.
The apes were shown one of two films in which a human actor looked for a hidden object in one of two locations. In both films, the actor saw where the target object was before searching for it in familiarization trials. Then, in the experimental trial, the object was moved from its initial hiding place either when the actor was present or absent. The viewing apes' eyes were tracked to see if they looked towards the place the actor would likely expect the object to be hidden or where it actually was.
And the researchers found that the apes would anticipate the human actor to act upon their belief of where the object was hidden, regardless of whether that belief was true.
"This study indeed provides strong evidence that the ability of apes to attribute false beliefs is much more sophisticated than even some of the study’s authors recently thought," Dr. Buckner says.
This study wouldn't have been possible without previous research conducted on human children, Frans de Waal, director of the Living Links Center at the Yerkes National Primate Research Center at Emory University, writes in a commentary on the new study.
Previous studies testing for false belief understanding in children also centered around similar hidden-object scenarios. Younger children were found to say that the actor (in that case a doll named Sally) would look where the child knew the object was, while children over the age of 4 would pass the test by saying the doll would look where she had last had seen it.
That study suggested that younger children couldn't understand when others held false beliefs, but scientists didn't leave it at that and further research contradicted those conclusions. In 2007, another team used eye-tracking technology – as in the ape study – and found that children as young as 24 months could correctly anticipate the actor's false-belief driven search.
"[The new study] is a great study especially since it moves us away from language dependency," Dr. de Waal writes in an email to the Monitor. Scenarios where researchers rely on lingual communication with the test subjects can be limiting as they may not understand the questions, he says.
Is predicting action enough evidence?
Robert Lurz, professor of philosophy at Brooklyn College and author of the book "Mindreading Animals: The Debate Over what Animals Know about Other Minds" who was not part of this research, is hesitant to say that this experiment proves the apes are understanding the actor's false belief about the location of the hidden object rather than simply picking up on other cues.
For example, he explains in a phone interview with the Monitor, perhaps the apes have learned that the actor always goes to the last place his gaze fell on the hidden object rather than fully comprehending that the actor thinks the object is still in that location.
This distinction between prediction and explanation is an important one, agrees Kristin Andrews, a professor of philosophy at York University in Toronto and author of "The Animal Mind: An Introduction to the Philosophy of Animal Cognition," who was not part of this study.
Yes, "they're tracking and anticipating people's behavior when people have false beliefs," she says in a phone interview with the Monitor. But it is possible that the ape can understand that the human has his or her own perspective even "without all the fancy conceptual baggage of being able to explain anything about what's going on in their heads."
Still, both Dr. Andrews and Dr. Lurz celebrate the new study as a significant step toward blurring the line between the cognitive capacities of humans and nonhuman apes.
If other explanations for the data can be ruled out, Lurz says, "it would show that this ability to attribute false beliefs to others, which has long been taken to be an essentially human ability, is also shared by our closest living nonhuman relatives, the great apes."
And that would imply that the last common ancestor of apes and humans also could understand false beliefs and possessed theory of mind.
This could also change the way humans interact with other apes, suggests Andrews.
"I think that the more that we know about these other species, the great apes, about their understanding of others, their concern for each other, their knowledge of each other will help us really rethink how we should see them as colleagues on this planet."