Another explanation focuses on the disconnect between how realistic something looks, and how well it moves. There's always been a lag time between how quickly designers can make things look like people, and how quickly engineers can make them move like us. If a figure that you thought was human started to move jerkily, you would recoil. Similarly, if you were to shake a robot’s hand while expecting a human touch, but instead felt cold rubber, you would be caught of guard. An unexpected break in humanness can be an unpleasant shock, one that sets off fearful and distrustful instincts. "Whenever we see something move, and we're not familiar with the mechanism of movement, it grabs our attention," says Andrew Olney, a psychologist at the University of Memphis who works on designing intelligent robots. "If your coffee cup started slowly moving across the table, that would kind of freak you out a bit."
Finally, a third theory turns to evolution. It suggests that if a robot looks like a human, but moves unnaturally, our brains subconsciously classify what we're seeing as someone with a disease. This is the same explanation proposed for most feelings of disgust. When we stand near something like faeces, rotting flesh, or a jerking robot, we experience a sudden urge to get away from it so as to avoid catching the infections it may harbour. Some preliminary research in rhesus monkeys suggests that these animals share an uncanny valley-like response, indicating that they have perhaps adapted to the same evolutionary pressure in the same way as us.
We are, of course, becoming more accustomed to robots and avatars in everyday life. Between games like Last of Us and movies like Avatar, we see computer-generated images of people all the time. Mori's original examples of uncanny objects, like a wooden prosthetic hand, probably wouldn't raise an eyebrow today because they are so obviously fake. Final Fantasy no longer triggers unsettling feelings among younger viewers, who are used to games like Crysis and Witcher 2. The shift in expectations has been going on all along – and might well continue until technology is good enough to fool us.
This trend sets up a roboticist’s ultimate challenge: to be the first person to build a robot that is indistinguishably human to other humans. It is a challenge that Hiroshi Ishiguro, one of the world’s leading humanoid roboticists, believes he will one day meet. Some of his humanoid robots already interact with people, and some robot designers treat them as if they were human. When one roboticist named Peter Kahn visited Karl MacDorman’s human-computer interaction lab at Indiana University and wanted to take apart Ishiguro’s Repliee Q1Expo, a petite Japanese humanoid-woman in a pink blazer, he first turned to his wife and asked, “May I touch her?”
But not everyone is convinced that we'll engineer our way out of the uncanny valley, or that it is a good thing if we do. While what makes us uncomfortable is likely to shift, the presence of discomfort won't, they argue. Potentially, it could get worse. "You can imagine cases, for example, maybe 50 years down the road, someone might be in a relationship with an android and not know it," says MacDorman. “But if there were an accident and some of the mechanical underpinnings are exposed, that would be uncanny. It would be uncanny in a different way.”