Macaques find fake monkeys creepy
Human suspicion of realistic robots and avatars may have earlier origins than previously thought.
The phenomenon, called the uncanny valley, describes the disquiet caused by synthetic people which almost, but not quite, match human expressiveness.
Experiments with macaque monkeys show they too are suspicious of replicas that fall short of the real thing.
The research suggests a deep-seated evolutionary origin for the reactions such artificial entities evoke.
The phrase the "uncanny valley" was coined by Japanese roboticist Masahiro Mori and shows that human disquiet increases as avatars and robots look more and more human.
Many people who watched films such as Beowulf, Polar Express and Final Fantasy: The Spirits Within reported that, despite the impressive 3D animated effects, the people portrayed were not entirely convincing.
Many explanations have been put forward for such responses, said Princeton neuroscientist Dr Asif Ghazanfar who carried out the research on the monkeys.
Some suggest the reactions are caused by a suspicion that those who look human but act oddly are ill and avoiding them makes good evolutionary sense. Others have advanced cultural reasons to explain the response.
"The range of explanations for the uncanny valley in humans is large and by doing this experiment we can reduce it quite a bit," said Dr Ghazanfar.
The Princeton team was led to investigate whether monkeys show uncanny valley responses because of work they were doing on the best way to investigate macaque communication.
Despite the avatars being simple, monkey reactions were consistent
"What we wanted to do was make a monkey avatar to interact with real monkeys. That would allow us to have real time social interaction occurring where we monitor brain activity in a real monkey," he said.
"Having an avatar gives us complete control over one side of the interaction which is unprecedented," Dr Ghazanfar told the BBC.
The reactions of real macaques to the artificial monkeys were intriguing, he said.
"We were not terribly surprised that they show an uncanny valley effect," he said. "What I am surprised by is that we can evoke it using such a rudimentary procedure - measuring simply how long they look."
"The animals were not trained or rewarded yet they were completely consistent in their reactions," he added. The results were reported in the journal PNAS.
Macaque monkeys are a favourite among researchers because of their biological similarity to humans. Their social lives have enough in common with humans to make comparisons apt, said Dr Ghazanfar.
Macaques have a "despotic" social network that means monkeys that are physically frail, old or sick are excluded.
It also suggests, he said, that human reactions to almost human avatars do have an evolutionary origin.
"I think there's a lot of interest in it because there's an increasing number of folks who are pursuing human interaction with artificial agents," he said.
"We can demonstrate that evolutionary hypotheses are tenable and that the uncanny valley has something to with social experience and neural processes across many primate species."
The Princeton team plans to keep on using artificial macaques to investigate monkey vocal communication.
"The positive spin is that we have made an avatar realistic enough that it has produced expectations from our real monkey," said Dr Ghazanfar. "The monkeys, like humans, quickly habituate to the creepiness of the avatar."