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How to creep out a monkey (or a human, for that matter)

a macaque monkey

With Halloween on the way, you might find yourself wondering how to look your creepiest. For a while robotics has had a theory about this: what you want to do is look almost like a human, but not quite. We’ve mentioned this theory before – it’s called the ‘uncanny valley’ and it says that as robots look more human we tend to like them more, but only up to a point. Sometimes a robot looks very close to a human, but not quite right. Humans find that sense of ‘not quite right’ creepy, and our comfort levels dip into the uncanny valley. Scientists have had a couple of theories in the past about what makes the uncanny valley work, but now scientists are starting to test them.

Most of the ideas people have had to explain the uncanny valley say that it’s related to humans’ evolutionary past. For example, it could be that when we see things that look almost but not quite human, they look diseased to us. It would make sense for us to have evolved to avoid things that don’t look right if we might be in danger of catching a disease from them. Another idea is that it’s more to do with attractiveness. We’ve evolved a sense for what makes a good-looking face, for example, and a robot that doesn’t meet that standard might look unattractive. Both of those ideas sound good, but how can you find out whether the evolution angle is right? Try testing them on some of our evolutionary cousins – see if the uncanny valley works on monkeys.

To set up the test, researchers got some images of monkey faces. Some of them were fake-looking, some were very realistic, and some were realistic-looking but not perfect. Then they showed the images to real monkeys to see which ones they would look at the longest. Humans tend to look longer at faces they find attractive compared to faces they find unattractive. Would monkeys do the same? It turns out they seem to. The monkeys preferred to look at the images that were either fake-looking or very realistic, rather than the faces that were in between. So it’s not just humans: monkeys feel the uncanny valley too.

It looks as though the explanation for why the uncanny valley effect happens does indeed have something to do with our evolutionary past. Which explanation is right, though, still hasn’t been decided. Finding out more about the uncanny valley will help robot researchers build robots feel more comfortable with. It will also help computer animators wondering how to make characters realistic without being unappealing, and of course, Halloween revellers looking for the creepiest possible costume. Based on the uncanny valley theory (and a look around YouTube), we recommend going as Robot Elvis.