Definition
The uncanny valley is the sudden creepy, uneasy feeling people get when a robot or computer-generated character looks almost, but not perfectly, human, instead of feeling friendly. The name comes from a curve: as a robot looks more human, we like it more and more, but just before it becomes nearly identical to a real person, our liking drops into a deep valley.
The moment a cute character turns creepy
A cartoon stuffed animal or a little wheeled vacuum robot makes us feel relaxed. We already know it looks nothing like a person, so we welcome it with no guard up at all.
But something strange happens when makers get ambitious and try to make a robot look just like a human. Add artificial skin and humanlike blinking, and at first people like it a little more with each upgrade. Then, once it gets vaguely close to the real thing, our liking falls off a cliff and turns into strong discomfort.
Pretending to be human while having slightly stiff eyes or unnatural skin texture gives you a chill, and you can't say why. It's not a perfect person, and it's not a cute doll either. When we face something we can't classify, an alarm goes off in our mind all by itself.
Why our brains sound the alarm
There are several theories about why this reaction happens. A leading one says that the moment we meet someone, our brain quickly checks, "Is this a real, living person?" This works as a cognitive defense mechanism that protects us by sorting out things that seem off.
A human face has dozens of tiny muscles that move naturally with our emotions. But even a sophisticated robot or 3D graphics character can't perfectly match those subtle expression changes and the rhythm of eye contact.
Our brains pick up on these tiny mismatches. Quite a few studies find that the discomfort grows when the humanlike and non-humanlike parts don't line up, such as when something looks human but its movements or gaze don't seem alive.
Modern technology tries to cross the valley
This phenomenon was first named in 1970 by Masahiro Mori, a Japanese roboticist, in an essay in the journal Energy. At first, only robotics researchers talked about it. Today it's seen as a key challenge in fields that create humanlike characters, such as 3D animated films, video game graphics, and AI virtual humans.
Some films that tried to create characters just like real people were criticized for awkward facial expressions, and this is often cited as one reason they did poorly at the box office. These films are often held up as examples of the uncanny valley trap. Audiences sometimes feel warmer toward a simple, cartoonish character than toward an attempt at perfect imitation.
To be more precise, in Mori's hypothesis the valley isn't a wall that can never be crossed. Once something becomes truly indistinguishable from a real person, our liking returns to the level we feel toward people. Still, experiments disagree about exactly when the valley actually shows up.
Common misconceptions
The more human-like you make a robot or character, the more people will always like it.
Liking rises up to a point, but when something is only awkwardly close to human, liking can plunge sharply into a valley.
Where you meet it
The chilly feeling you get looking at a lifelike, life-size figure in a wax museum.
Characters in early 3D animated films that people called creepy because their facial expressions looked unnatural.
The awkward feeling when an AI virtual human's gaze or mouth movements are slightly off.
In one sentence
It's the unease and creepiness we feel toward robots or characters that look almost human. A leading explanation is that our brain gets confused while judging whether something is human or not, though there are several theories about the cause.