This look at the computer graphics of "Terminator Salvation" does a good job of illustrating the "uncanny valley" between humans and robots:
Hollywood and robotics researchers have long struggled with the "uncanny valley," where a movie character or robot falls into the unsettling gap between human and not-quite-human.
One psychologist likes to demonstrate this by holding up a plastic baby doll and asking audiences if they think it's alive. They say no.
Then she takes out a saw and starts cutting the doll's head off, but quickly stops upon seeing the uncomfortable audience reactions.
The uncanny valley isn't just about physical appearance, it's also related to all the other nuances of behavior we can perceive in each other.
"There are some people who say it's simply not true," MacDorman said. "I don't fully agree with that, because I think there's definitely something to the uncanny valley — but there's a problem with a simplistic view of the uncanny valley."
No one knows what it means to have 70 percent or 90 percent human likeness, MacDorman pointed out. Perhaps all the attributes of a robot, ranging from the eyes to body movement to voice tone, might have 90 percent resemblance to human characteristics.
Or a robot could be 99 percent perfect, except for a delayed reaction time during conversations with humans.
That could still trigger the uncanny valley sensation in observers who would quickly conclude that the robot was retarded, if not — gasp — non-human.
The "uncanny valley" concept is primarily just a way to label the "I know it when I see it" heuristic we use to recognize other humans. Even more interesting questions lie waiting on the other side of the valley: if a robot appears human and acts human and is indistinguishable from a human during typical interactions, do we have to treat it like a human?
(I say no.)