“Creepy” may be the more apt colloquial term, but “uncanny” is how scientists describe the feeling you get when looking at an almost-but-not-quite-real-enough simulation of a human’s face. It may be a robot, the AI in your favorite video game, or that CG version of Jeff Bridges, but there seems to be an unusual feeling we get from seeing a face that “just isn’t right.”
For example, in a study by Seyama and Nagayama (2007), the researchers note that abnormally large eyes on face with higher degrees of realism induce an “uncomfortable (unpleasant) impression.” Below is a general, graphical representation of this effect, and that dip is called the “uncanny valley.”
One theory behind this occurrence is that we have been evolutionarily programmed to avoid corpses, therefore we have a gut reaction to faces that just aren’t right. The visual artists for the film The Curious Case of Benjamin Button had the challenge of crossing this valley, and it’s generally accepted that they did very well in this endeavor. Seems like those millions of dollars paid off, at least in terms of modern computer generated imagery.