London Telegraph 
November 26, 2013
We humans have evolved to relate emotionally to inanimate artefacts, which is strange when you think about it. Children play with dolls and toy soldiers as if they were people. Adults talk to their cars. As long as they are robot-like and “mechanical”, we are comfortable around them, and can display affection (as for an old car). But when it comes to human-like robots, something unnerving happens.
As they acquire more human-like features, our affection wanes and we begin to get a creepy feeling. Our liking turns to revulsion. Androids that look too human freak us out.
This odd phenomenon is called the “uncanny valley”, and it has befuddled engineers and scientists who design robots and interactive software. The term comes from the dip in a graph with two parameters: psychological familiarity and human-likeness.
As human likeness increases, so does our familiarity, or affection, for an artefact. As soon as the resemblance becomes too acute, though, familiarity drops below zero – hence the “valley”.