Odds are, if you play video games, watch computer-generated animated films, or know anything about robotics, you're familiar with the term uncanny valley. It's typically used to describe the eeriness we feel when something looks human but clearly isn't human. Maybe the eyes are dead and soulless. Maybe the motion is too mechanical, creating a gap between what we're seeing and what our brain expects. Surprisingly, given how widely known the uncanny valley phenomenon is, there's a lot of conflicting research about what triggers it--and even whether it exists at all.
The BBC has put together a great study of the uncanny valley that includes the concept's 1970 origin. Back then, rubber-skinned robots and not-quite-human CG characters weren't commonplace like they are today, but a Japanese roboticist wrote a paper that spawned the popular term. Since the original article was written in Japanese, however, the uncanny valley as we know it may only partially resemble what roboticist Masahiro Mori actually meant.
Writes the BBC: "Contrary to popular belief, his original title 'Bukimi No Tani' only roughly translates into the phrase it has made famous. A more accurate translation is 'valley of eeriness.'
"This matters because it demonstrates the problem with the uncanny valley: it is an inherently woolly idea. When researchers try to study the phenomenon, they often have a hard time pinning down what an uncanny response actually looks like. The main graph in Mori’s paper has been mistranslated many times, leaving many people unsure what he really meant. Mori used the Japanese word 'shinwakan' on the y-axis, a word that has no direct translation into English. The most common interpretation is 'likeability,' but not all translators agree about that. Other suggestions include 'familiarity,' 'affinity,' and 'comfort level.' "
This part is even wilder: Mori's paper was not a study that involved careful scrutiny of how people looked at robots. It was just his projection, and the idea took hold, which means we've been referring to the uncanny valley for decades without much data to back it up. No surprise, then, that the uncanny valley can be a pretty nebulous term. As the BBC points out, some studies have shown that people react positively to robots making human-like expressions.
Perhaps the most interesting study the BBC references makes the case that the uncanny valley should be more of an uncanny cliff. According to researcher Christoph Bartneck from Canterbury University, "at the point where robots achieve extreme human-likeness, but remain discernibly un-human, their likeability plummets. And people only start to like them again when they become so human-like that they escape detection."
The rest of the article digs further into explaining why we react to the uncanny the way we do, citing evolution as a possible answer. Apparently rhesus monkeys have a similar uncanny valley response to some stimuli. It took a few decades, but the science community is now very interested in finding out what exactly triggers an uncanny valley response. Hopefully they'll figure out it out before vaguely human robots are all over the place.