That Uncanny Valley

Uncanny Valley

A concept formulated by Masahiro Mori, a Japanese roboticist. Mori tested people's emotional responses to a wide variety of robots, from non-humanoid to completely humanoid. He found that the human tendency to empathize with machines increases as the robot becomes more human. But at a certain point, when the robot becomes too human, the emotional sympathy abruptly ceases, and revulsion takes its place. People began to notice not the charmingly human characteristics of the robot but the creepy zombielike differences.
—John Seabrook, "It came from Hollywood," The New Yorker, December 1, 2003

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.