Masahiro Mori's original description of the uncanny valley is relatively straightforward: We like artificial beings more when they appear more humanlike, but we really dislike them when they appear almost perfectly human with a few subtle flaws. But looking deeper at this phenomenon reveals a lot of complexity in the concept, not least of which is simply figuring out exactly what Mori meant in his original publication on the theory.
Mori's essay "Bukimi No Tani" was first published in the Japanese journal Energy in 1970, but the uncanny valley didn't become a popular concept in the West until the article was translated to English in 2005. Even then, the essay wasn't rigorously translated until 2012 (the first translation wasn't intended for publication), which meant our initial understanding of the uncanny valley concept wasn't completely correct [source: Hsu]. First, bukimi might be translated more accurately as "eerie"instead of "uncanny," but the "uncanny" terminology is too well-known to disregard. More importantly, the term Mori used for how much we like artificial humans, shinwakan, is not easily translatable. The original translation, "familiarity," doesn't fully capture Mori's intent. Researchers have instead adopted the term "affinity," suggesting that shinwakan is a blend of both familiarity and likability [source: Kätsyri].
Mori placed several examples of objects with human appearances along his uncanny valley graph, including industrial robots, toy robots and prosthetic hands. Many are particular to Japanese culture, such as bunraku puppets and Okina masks. While these may be perfectly valid examples, they can be difficult for Western researchers to study and understand.
Finally, Mori suggested a possible reason for the uncanny valley effect: He placed corpses and zombies at the bottom of the valley on the graph, and suggested that we experience unease at not-quite-accurate human simulations because they remind us of corpses and we naturally fear death.
Mori's concept of the uncanny valley was based on his own ideas of how humans might interact with humanlike robots, not on statistical studies of human/robot interactions (which would have been difficult to conduct in 1970). But his hypothesis, which we'll break down in the next section, set off a wave of further research into the phenomenon.