"The Polar Express" Would Creep Out Monkeys Too?

Maggie Koerth-Baker
for National Geographic News
November 3, 2009

If you've seen The Polar Express—or even a too-human robot—you may have already crossed the "uncanny valley."

Related Video: The Polar Express Trailer

The term refers to the negative psychological response—aka the willies—that many people have when they see an image of a human face that's apparently too close to reality for comfort.

Now researchers have documented evidence that monkeys may experience a similar sensation. The discovery could lead to better brain studies and eventually shed light on why our mental geography includes an uncanny valley.

Monkeys Preferred Faker Fakes

At Princeton University's Primate Neuroethology Laboratory, five male long-tailed macaques were shown three moving macaque faces on a monitor—one actual video of a macaque; one unrealistic, robotlike animated face; and one realistic animated face.

The monkeys looked more often, and longer, at the real deal and the unrealistic fake, study co-author Asif Ghazanfar said.

"This is anecdotal, but they seemed to even avert their gaze from the realistic fake face, like they didn't want to look at it," said Ghazanfar, a Princeton psychology professor.

(In other news, long-tailed macaques teach their young to floss with human hair [includes video].)

Ghazanfar and his team didn't use any methods of tracking emotion, so the study doesn't prove that the realistic fake face gave the monkeys the heebie-jeebies.

However, the research does suggest that, given the choice, monkeys prefer to look anywhere other than at a realistic fake monkey. This is what you'd expect if the uncanny-valley theory holds for macaques, Ghazanfar said.

Evolution Uncannily at Work?

The discovery may be important, for a couple of reasons.

First, Ghazanfar said, it provides evidence supporting the theory that the uncanny valley is not a result of cultural preferences—it's hardwired into our heads.

The response could be an evolutionary adaptation passed down by our primate ancestors—though it doesn't immediately appear to serve any useful purpose.

Maybe it's simply a side effect of being evolutionarily wired to pay close attention to human faces, he said. When we see a face that's close enough to "correct," our brains want to classify it as human. But subtle off-kilter details prevent that from happening, and the resulting dissonance results in the uncanny valley, the thinking goes.

Detour: Fake Monkeys to Avoid Uncanny Valley

Finding an uncanny valley in monkey psychology will also help Ghazanfar's team develop more accurate ways of collecting data on electrical brain activity during communication. In fact, that's why they did the study to begin with.

Currently, Ghazanfar said, studying primate brain function means humans have to coax a monkey to repeat the same task over and over—not exactly a replica of natural social interaction.

But now that the scientists know what monkeys do and don't like to look at, his team can create a virtual monkey that can engage the test subject in the macaque equivalent of a casual chat, while allowing researchers to control the conversation.

Eventually, Ghazanfar hopes, the monkey brain studies could shed light on human disorders, for example by pinpointing how electrochemical misfires might lead to communication problems between humans.

Findings published October 12 in the journal Proceedings of the National Academy of Sciences.

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