In 1970, Japanese roboticist Masahiro Mori argued that humans find humanoid robots appealing only up to a point. As robots start to look more and more human, there’s a moment at which they reach a strange middle ground—they appear mostly human but are still identifiably “other.” Mori called this moment the “Uncanny Valley.” 

New York Magazine explains, “Whereas a robot like Wall-E can be easily parsed by our brain as being robotic, those in the uncanny valley often … elicit feelings of unease because they’re close to being human, but not.”

Though the theory has become increasingly popular over the last few decades, there has been little empirical evidence to back it up. One 2011 study of subjects' response to lifelike robots suggests the effect may come from the brain's inability to reconcile a convincing appearance with robotic motion. A systematic review of the research on the phenomenon conducted this year concluded that “empirical evidence for the uncanny valley hypothesis is still ambiguous if not non-existent,” but that a perceptual mismatch between artificial and human features might be to blame.

Though the jury is still out, interest in the subject continues. Recently, two researchers, Maya B. Mathur and David B. Reichling, ran a new study to determine how humans respond to robots that have varying levels of human appearance. 

They started by pulling photographs of the faces of 80 real robots. Their first test simply asked volunteers to rank the robots based on how human or mechanical they seemed, and whether they seemed to be expressing a positive or negative emotion. Their second and third tests, meanwhile, got to the heart of the uncanny valley question, asking volunteers to rank how “friendly” or “creepy” each robot seemed. They found that as faces started to look more human, volunteers at first described them as more likable. But just before the robots became nearly indistinguishable from humans, likability ratings dipped—showing that subjects were having an uncanny valley reaction to the humanoid robots. 

Next, Mathur and Reichling ran experiments to determine how people perceive robots they actually interact with. Testing for perceived “likability” and “trust,” the researchers found that, once again, likability dipped significantly when robot visages entered the uncanny valley. Trust, meanwhile, dipped slightly, but not nearly as much as likability. 

While more research is needed to interpret these preliminary findings, Mathur and Reichling’s study found significant support for Mori’s original hypothesis. So if you get creeped out by humanoid robots like Bina48 or the baby robots used in a recent psychology study, there's now more evidence to explain that feeling. 

[h/t: New York Magazine]