The poets and philosophers were right, the eyes really are the windows to the soul. Or at least what we perceive to be the soul. Researchers at Dartmouth College have studied how people respond to images of humans, dolls, and the morphed blending of the two to learn how realistic a face must be before we’ll consider it to be alive. Turns out that you have to be about two-thirds the way between human and doll (towards the human side) before people will stop thinking you’re an object and start treating you like a person. Not only did the Dartmouth scientists roughly determine the boundaries of the Uncanny Valley, they studied how subjects were making their decisions. Short answer: it’s all in the eyes. You can look at examples of the images that test subjects were asked to judge in the videos below. If you watch closely you can see a face go from caring to creepy to cute and back again all in a few seconds. Block out the eyes and it almost seems like you skip “creepy”. Cool.

The study was performed by Christine Looser, a Dartmouth PhD student, and her advisor Thalia Wheatley and appears in a recent issue of Psychological Science. Wheatley’s Lab examines a wide range of questions on how humans relate to one another. For this experiment, Looser took human faces and matched them to the faces of dolls that most closely resembled them. Then the two faces were morphed together with photo-altering software to produce a series of images that exist along the human-doll continuum. The following videos show two examples of what it would look like to scan across that continuum and back again. The subjects in the study, however, were shown still images.

Test subjects would look at a photo taken from the human-doll continuum and be asked if the picture shown was a doll or human. Two months later, the same subjects were asked to look at the same images and determine if the person shown had a mind. Looser and Wheatley found that images start to be perceived as human, and possessing a human mind, about 67% along the continuum. In other words, if a face gets any more doll-like than that, people will no longer believe it is alive.

A different experiment determined that test subjects looked longest at the image’s eyes, rather than the mouth, nose, or skin, before categorizing an image as human or doll. From that focus Wheatley and Looser suggest that the facial cues humans use to recognize living things are clustered around the eyes, though not necessarily on the eyeball itself. By studying those clues, humans are able to quickly determine if a face belongs to another person or if it’s simply something that looks like a face by accident. This discernning skill is what probably kept our evolutionary ancestors from talking to human-looking rocks while still being able to form bonds with their family members.

I always find this kind of psychological research fascinating, though I worry about certain limitations of the study. Let’s skip my general disapproval of using student volunteers as test subjects (ask me about this when you see me at a conference and we’ll discuss it for hours, trust me) and just focus on the breadth of the experiment. By design Looser and Wheatley were only interested in static visual cues. This ignores the importance of faces in motion (though they’ve looked at the human response to moving objects in other experiments), and doesn’t address audio input. A doll that appears 2/3 human is still going to be really creepy if it moves in a jerky way, or if it sounds like Stephen Hawking. Measuring when humans will accept a static image as a person is valuable data, but it’s only part of the understanding that we need.

Robotics engineers and digital artists struggle with creating realistic-looking artificial humans that viewers will respond to positively. Hollywood will typically make their characters cartoonish to avoid the Uncanny Valley, though recent attempts such as Avatar seemed to push the boundaries of what could be accomplished. With robots, the Uncanny Valley at times seems like an insurmountable obstacle – some of the life-like faces created seem almost acceptable while others will make your skin crawl for days.

Researchers like Looser and Wheatley have given us valuable insight into how we can create artificial people with which we can identify. However, there is still a lot of work to be done before we’ll be able to truly make robots and virtual characters appear more human than fake. Even then, it will take years before we can give them personalities that we will want to love. In the meantime, I think I’m going to work on creating an augmented reality iPhone program that removes the eyes from images of people. I’ll call it; “The Creepiest Freakin’ App You’ll Ever Own.” Should be a hot seller next October.