Let’s face it: there are just some things that are universally unsettling. Dolls, ventriloquism dummies, mannequins, and humanoid robots all tend to create this uneasy feeling in us – sometimes, we’re even afraid of them, despite the fact that they aren’t really alive.

This effect, and the feelings associated with it, are known as the uncanny valley.

Though it began as a simple psychological curiosity, the uncanny valley has become a huge concern in the fields of computer animation, robotics, and artificial intelligence.

But why does this happen? What happens to our brains when we see something that isn’t quite human? Let’s take a look.

Residents of the Valley

The first mention of the phenomenon appeared in an essay written by robotics professor Masahiro Mori in 1970 entitled Bukimi no Tani, or The Valley of Eeriness.

He was writing primarily about the feelings that arose when he looked at figures, but the term would eventually apply to dolls, ventriloquism dummies, and robots. The English term was first coined in “Robots: Fact, Fiction, and Prediction”, a 1978 book by Jasia Reichhardt. Since then, research into the effect and how to avoid it has grown exponentially – there were 510 separate academic papers that mentioned the effect published in 2015.

Entities that trigger the effect tend to share a particular set of traits. They are meant to mimic humans, but discrepancies in their vocal patterns, movements, or appearance make it so that they aren’t quite perfect replicas of human beings. This near-realism sets off a reaction in our brains that varies from discomfort to deep revulsion. But why? What’s going on?

It’s Just a Design Flaw

The most basic explanation for the uncanny valley effect is that there’s something hardwired in us that causes us to be repulsed by things that look human, but aren’t quite there.

Some theories tie it to an instinct called pathogen avoidance – basically, we’re programmed to avoid things that look unhealthy or diseased to prevent the spread of possible pathogens. This is why it’s so easy for us to be afraid of zombies – despite the fact that they were once human, they move sluggishly and are clearly diseased.

Mismatched expressions between the eyes and mouth, or a lack of emotion in the eyes altogether is thought to denote psychopathy – considering that many simulated humans lack eyeballs that function like ours do, this is a common problem that plunges simulations into the uncanny valley.

Deviation from social norms in the eye contact, movement, or voice modulation could also denote psychopathy. Serial killers like Hannibal Lecter are often given these traits to make them less human than the people around them, and thus make our feelings towards them almost entirely negative.

Psychological Issues and Existential Crises

Some theorists believe that the entities in the uncanny valley straddle the lines between our categories of “human” and “not human”, or perhaps “alive” and “not alive”.

This incomplete movement from one category to another causes a sort of “error message” in the brain, which reacts with revulsion and an instinct to reject the stimulus.

If something looks human, we expect it to be human, but things that reside in the uncanny valley can never satisfy that expectation. This theory applies in the case of “living” dolls such as Chucky – their status as something that should not be living, but nevertheless moving around, and speaking, makes them deeply unsettling for us.

Finally, the existential issues that entities from the uncanny valley could provoke are also cited as a possible reason for the discomfort. Some think that the movement or looks of these entities could remind our brains of corpses, and thus invoke an ingrained fear of death.

Another possibility is that we unconsciously begin considering the humanity of these beings, and thus of ourselves – an uncomfortable conversation for most people.

Though this concept is usually addressed in science fiction with movies like I, Robot, horror can easily employ this in the case of things like ghosts and other spectral beings.

The Valley in the Media

In 1988, Pixar released a short film entitled “Tin Toy”, featuring a computer-animated infant called Billy. The appearance of the infant descended so far into the uncanny valley that Pixar turned away from making human characters completely for a while, instead focusing on living toys, robots, insects, and other non-humans that stood up better when computer animated.

Since then, computer-animated humans have often been decried by audiences as “creepy”, and this has a devastating effect on the films in which they feature. However, there’s a certain genre that has created uncanny valley residents time and time again with no repercussions – the horror genre.

In an industry that relies on creating unease and fear in its viewers, the uncanny valley is a gold mine. Characters like Jason Voorhees and Michael Myers wear frightening, corpse-like masks that strip them of their humanity and make them even more frightening.

Faceless creatures like Slenderman haunt the forests and backyards of frightened children. The uncanny valley is horror’s bread and butter, even though we barely understand it. With the promising research being conducted into the phenomenon nowadays, the possibilities for scarier horror villains is endless.

Hope for the Future

Despite its beginnings as an interesting thought exercise for psychology majors, the uncanny valley is a new frontier for the horror genre. Though much of the research being conducted now is aimed at bypassing the valley, the results could assist horror authors and directors in creating villains and monsters that crawl through nightmares more effectively than ever before.