What makes a virtual face appear alive? According to a recent study published in Psychological Science the eyes are the most important factor in imparting life to the lifeless.
You can apply all the photorealistic textures you want to a 3D model, animating even the smallest facial tics, but without lifelike eyes your virtual human isn't much more than a puppet. At best it will just look silly. At worst it falls into the realm we call the uncanny valley, so close to life that its flaws are truly disturbing to the viewer.
"There's something fundamentally important about seeing a face and knowing that the lights are on and someone is home," says Thalia Wheatley of Dartmouth College, who co-wrote the study with graduate student Christine Looser.
Wheatley and Looser conducted their study by photographing doll faces at toy stores, matching them with similar human faces, and then morphing between the two. You can see this in video form below.
Volunteers were shown pictures of this process and asked to determine which pictures were human and which were dolls. The study found that around two-thirds of the way between doll and human was the point where volunteers started seeing real life in the pictures.
A separate experiment determined that of all of the facial features, the eyes were the most important in determining whether an image was of a real living creature. As you can see in the video, the eyes start going noticeably out-of-proportion once it hits a third of the way from human to doll.
The study reminds me of a time when I was playing through Ninja Theory's Enslaved with my older brother. He continuously marveled over how lifelike the characters looked. During one particular cut scene he blurted out, "The eyes! It's their eyes. They look so real!"
Are the eyes the portal to the soul? They certainly seem to be a sure indicator of the soulless, and when we find ourselves disturbed by a virtual human treading through the uncanny valley, perhaps it's because we're looking for something that should be there but simply isn't.
"I think we all seek connections with others," Wheatley says. When we recognise life in a face, she says, we think, "This is a mind I can connect with."