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uncanny valley

What is the uncanny valley?

The uncanny valley is a common unsettling feeling people experience when androids or humanoid robots and audio/visual simulations closely resemble humans in many respects but aren't quite convincingly realistic.

The phenomenon is a consideration in several areas of design, including robotics, video game art, training simulators and three-dimensional animation. Depending on the intent, a designer might want to avoid the uncanny valley or exploit it to elicit a particular response.

The uncanny valley is named for the way the viewer's level of comfort drops as a simulation approaches, but doesn't reach, verisimilitude -- the appearance of being real. Simulations that lack significantly real aspects of reality don't tend to elicit this response, nor do simulations that simulate reality to a degree that satisfies the viewer. Near-realism and mixes of realism and surrealism most often cause this eerie sensation. The effect is intensified if the simulation is moving.

The uncanny valley is an important concept when designing dolls or robots, making movies or designing video games. For example, a robot that's designed to help people calm down a patient who lies in the uncanny valley might cause further discomfort for that person. Likewise, a computer-animated film might cause an uncanny valley feeling when its human-animated characters are designed to closely resemble humans, but they don't move like a human would. This could cause the audience to feel a sense of unease or disgust. However, if the movie is a horror movie, the uncanny valley feeling could add to a villain's on-screen presence.

Below is a plotted graph of viewer responses to increased realism, illustrating the uncanny valley.

A graph depicting the uncanny valley.
The closer something gets to looking human but stops right before it reaches a realistic look, the more it falls into the uncanny valley.

History of the uncanny valley

Japanese roboticist Masahiro Mori wrote about the uncanny valley effect in a 1970 essay, "Bukimi no Tani," which translates roughly to valley of eeriness. As a child, Mori never liked looking at wax figures because they looked creepy. In the essay he contributed to, Mori wrote about the uncanny valley in relation to robots after observing that the electronic prosthetic hands being developed at the time triggered the same feeling.

The uncanny valley as a concept originated with Mori, but this general feeling predates him, as historical figures such as Charles Darwin have written about experiencing similar feelings.

The English term uncanny valley was first mentioned in the 1978 book by Jasia Reichardt titled Robots: Fact, Fiction, and Prediction.

Mori's original essay focused on robot design, but it later began to be applied to any humanlike object or image.

Implications of the uncanny valley

The emotional response diagrammed in the uncanny valley can reach extreme levels such as revulsion, exceeding those responses experienced when a person views a corpse. Different people experience the uncanny valley at different levels, depending on the familiarity of the subject matter. Designers can bridge the valley with changes like adding cartoon-like or cuter facial features.

The uncanny valley phenomenon usually refers to human simulations but also can be created by Photoshopped images, dolls, teddy bears and subjects of plastic surgery. The uncanny valley can also be created by discrepancies in voice, movement or appearance.

In robotics, it's important to design products that don't create distrust between the robot and the user. Designs that fall into the uncanny valley might be poorly received and ultimately be less helpful in their intended purpose.

In film, unrealistic computer-generated imagery might cause a disconnect with the viewer at best. At worst, it can cause feelings of discomfort, prompting the viewer to consider the movie negatively overall.

In game design, unrealistic depictions of human characters can have the same effect on players as in films.

In toys, a doll or similar figure can fall under the uncanny valley, causing it to be ignored and disliked by the owner -- or not purchased in the first place.

Examples of the uncanny valley

The phenomenon of the uncanny valley can be observed in many different areas. It's possibly the easiest to spot in films.

For example, many people felt the 2019 film adaptation of Cats fell into the uncanny valley. The film featured human actors with CGI added to their bodies and faces to look like cats. Their movements were directed to look more cat-like, creating a discomforting and revolting response from some viewers. The review aggregator Rotten Tomatoes gave it a critic score of just 19%, with many of the negative reviews citing the unsettling character designs.

Another film that fell into the uncanny valley was the original trailer for 2020's Sonic the Hedgehog. The live-action movie featured a computer-generated (CG) animated version of the character Sonic. Unfortunately, the viewer feedback from the initial trailer was so negative, and the character design reached so far into the uncanny valley, that they changed Sonic's design mid-production.

An example of the uncanny valley in the robotics field is Telenoid R1, which is a robotic communication device. It has a minimalistic design and is the size of a child, has a bald head, smooth skin, no limbs and a blank face. The goal of this robot was to create a portable humanlike device to communicate with other humans remotely. Although it's an interesting idea, many people found the not-quite-lifelike design creepy, falling into the uncanny valley.

Avoiding the uncanny valley

The uncanny valley effect can be caused by several factors, such as the ambiguity of something being almost but not quite human; mismatching elements, such as a voice not matching the face or appearance and movements; and inconsistencies in portraying human likeness, such as slightly unrealistic eyes or facial movements.

When designing a robot, a doll or anything else that has a humanlike representation, it's important to keep these factors in mind, as the success or failure of a product partially relies on whether it falls in the uncanny valley.

The uncanny valley can also be created by the uncertainty of determining which category something belongs to. For example, the movie Cats features humans with CGI cat features like whiskers, fur, ears and tails, making the intent unclear of whether they're supposed to represent human beings or cats.

The uncanny valley can be reduced by moving away from combining features that are on different sides of a boundary. For example, the character Wall-E from the movie of the same name is a CG robot designed to look more like a robot, but with a personified personality, making the character feel more likable. Likewise, many of the Marvel movies integrate CGI into their characters, making them sometimes look realistic enough that viewers might not initially realize they're looking at CG.

To make a robot or other personifiable object more realistic, it's important to ensure the object's movement matches its facial expressions and tones of speech. Any movements should be responsive and as close to real human movement as possible.

Uncanny valley research

Mori originally didn't explore the existence of the uncanny valley effect as a scientific concept, and its validity as such is still debated. There have been several studies to prove the theory, identify its cause and measure it -- some with conflicting evidence. Additionally, individuals seem to experience the uncanny valley differently, making it more of a subjective experience. Some, like Mori, have suggested that the uncanny valley could be due to an evolutionary response to potential threats.

For example, a 2013 study in Computers in Human Behavior found evidence supporting the idea of the uncanny valley relating to the concept of the eeriness of digitally created faces that have a human likeness. This study found there was a linear relationship between likeness and eeriness related to facial proportions and realism. While this study found a linear relationship pertaining to the uncanny valley, other studies have found the valley to be more of a cliff; coming to the conclusion that the eerie feeling is more of a sudden feeling than a linear one.

The advent of artificial intelligence-powered chatbots has added another possible avenue for creating an uncanny valley for users. Learn more about how to build a chatbot that can avoid the uncanny valley.

This was last updated in February 2024

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