Uncanny valley n. Feelings of unease, fear, or revulsion created by a robot or robotic device that appears to be, but is not quite, human-like
... the phrase uncanny valley was coined by Japanese roboticist Masahiro Mori (in 1978, but possibly before that), who sums up the feelings that can occur in the uncanny valley succinctly:"If you shake an artificial hand [that you perceive to be real] you may not be able to help jumping up with a scream, having received a horrible, cold, spongy, grasp." —quoted in Jasia Reichardt, Robots: Fact, Fiction, and Prediction, Thames and Hudson, 1978
Why a valley? Because if you graph people's emotional reactions to a robot, they will generally increase (become more positive) as the machine's similarity to a human being increases. However, at the point where the robot is nearly lifelike, a certain creepiness or even downright revulsion takes over and the emotional response collapses. If the robot could be made 100% human-like, then the emotional response would, of course, return to the favorable range. That emotional crash at the not-quite-human stage is the uncanny valley.
Source: wordspy. See also The Uncanny Valley.
