What makes realistic robots so creepy?

A humanoid robot plays ball at the 2012 Robotica Humanoid and Service Robots Expo in Milan, Italy in November 2012. See More Robot Pictures.
┬ęPier Marco Tacca/Getty Images

Since Karel Capek coined the term "robot" in his 1920 play "Rossum's Universal Robots," robots have been regular fixtures in science fiction. And nowadays, they are becoming science fact. Robots are used to vacuum floors, build cars, deactivate bombs, assist in surgery and help the disabled, among many other functions. They are more prevalent than many of us might think, and they're poised to become even more ubiquitous in the future.

A robot, at its simplest, is a machine that can perform tasks normally undertaken by people. Some are operator controlled and some move autonomously (at least for as long as their power sources will allow). They range in form from single robotic arms to fully humanoid bodies. One of the major goals of some roboticists is to make robots appear more humanlike, at least in part to facilitate more natural interaction between robots and people. A robot whose appearance and actions mimic those of a human being more closely than its metal-skinned counterparts is often called an android.

There are a host of androids in existence that are being used in research today, like Repliee Q2, developed by Hiroshi Ishiguro of Osaka University. Repliee Q2 was modeled on a female TV announcer, and at first glance could be mistaken for a person. She can't walk, though, and doesn't incorporate any sort of complex AI, so her interaction capabilities are limited. Ishiguro has also created a remotely controlled android copy of himself named Geminoid HI-1 that he can use to give lectures from afar. And David Hanson has created an android modeled after Philip K. Dick, author of the novel "Do Androids Dream Electric Sheep?"which incorporates facial recognition and can carry on conversations. Though none have achieved true autonomy, a walking, talking humanlike copy of man almost seems the inevitable conclusion of such efforts. But, for some reason, when we encounter robots that look too much like us, we usually find them eerie or off-putting.

What is it that causes realistic robots to creep us out? Are we afraid of what a being with human capabilities, but without human conscience, might do? Are we afraid of the challenge they represent to our uniqueness, and that they'll end up replacing us? As likely as these reasons sound, given the human-dominating nature of androids in the bulk of science fiction, the most convincing answer to date seems to have a visceral rather than a philosophical cause. It's called the "uncanny valley" effect. Read on to find out more.