Why humans and other primates are freaked out by The Polar Express movie

The Uncanny Valley – Scary Dental Training Robot

Monkeys are freaked out by almost-but-not-quite-real depictions of themselves. That tendency is well documented in humans, but has never before been seen in another species. This behavior is called the "uncanny valley" hypothesis.

The “uncanny valley” was identified in 1970 by Japanese roboticist Masahito Mori, who noticed that people presented with likenesses of increasing realism respond with increasing empathy, right up to the point where the likenesses are almost real. At that point, people are repulsed. The sudden dip in graphs describing their response gave the phenomenon its name.


Many explanations have been suggested for the uncanny valley, which has also been blamed for the box-office failure of movies like Beowulf and Final Fantasy. Perhaps almost-real humans look a bit too much like corpses for our comfort; perhaps they’re so real that they engage our brains’ mate-recognition or disease-avoidance systems, which promptly identify poor partners or sick individuals.

To test their preference, researchers showed macaque monkeys real pictures, digital caricatures and realistic reconstructions of other monkey faces. To the latter, the macaques repeatedly averted their eyes.

“The visual behavior of the monkeys falls into the uncanny valley just the same as human visual behavior,” wrote Princeton University evolutionary biologists Shawn Steckinfinger and Asif Ghazanfar in a paper published (2009) in the Proceedings of the National Academy of Sciences.

The uncanny valley hypothesis posits that when robots and other human facsimiles look and act almost like humans, it causes a response of revulsion among human observers. The “uncanny valley” refers to the dip in the graph of the positivity of human reaction as a function of a robot and other human facsimiles’s life-likeness (above).

Hypothesized emotional response of human subjects is plotted against anthropomorphism of a robot, following Mori’s statements. The uncanny valley is the region of negative emotional response towards robots that seem “almost human”. Movement amplifies the emotional response.

It is the reason why we prefer cartoon characters than CGI characters that look realistic. For example, you are more likely to like the cartoon version of Homer Simpson than the “realistic” Homer Simpson.

Read about the uncanny valley hypothesis here.

Now this is the interesting part. Using long-tailed macaques (Macaca fascicularis) as test subjects, Steckenfinger and Ghazanfar (2009) found that these monkeys’ visual behavior actually fell into the uncanny valley, which mirrors the behavior of humans. These macaques looked longer at real faces and unrealistic synthetic faces than realistic synthetic faces.

The unrealistic synthetic faces, realistic synthetic faces and real faces. Actual images used in Steckenfinger and Ghazanfar’s experiment.

The authors did not conclude why the visual cues of these macaques fall into the uncanny valley, though they did suggest that it has an evolutionary basis.

Source: primatology.net