The ability to detect and understand other minds is critical for our physical and social survival. The big mystery is how our brains do this --that is, how do we tell a "Who" from a "What"?
To find out, we created doll-human continuua (click here to see a movie example of our stimuli). We wanted to know where, along these continuua, the face starts to seem alive.
THE TIPPING POINT
We found a consistent tipping point: a face had to be at least 65% human before people would say that it was more human than doll. Note that this is significantly different than 51% human -- the mathematical tipping point for a 0-100 continuum. People are stringent about what counts as alive. The same tipping point occurred whether people were asked if the face "had a mind", "could form a plan," or was "able to experience pain", indicating that recognizing life in a face is tantamount to recognizing the capacity for a mental life. Looser & Wheatley (2010)
THE EYES HAVE IT
"I looked for the moment when the face looked back"
It turns out that finding another mind requires scrutinizing one particular facial feature: the eyes. Seeing a single eye was enough for participants to judge the presence of life. In contrast, an equal-sized view of the nose, lips, and a patch of skin were far less useful (Looser & Wheatley, 2010). Indeed, as one participant put it "I looked for the moment when the face looked back at me." This suggests that the age-old aphorism is correct: we consider eyes to be "the windows to the soul."
This natural perceptual scrutiny --for fine ocular cues that convey a mental life --may help explain why eyes are the achilles heel of computer graphics imagery.
FACE - THEN - MIND
Although we may be experts at detecting a mind in a face, this visual scrutiny takes longer than detecting a face. Face detection is associated with an increased electrocortical response to faces about 170ms after the image first hits the retina. This well-documented, face-specific response occurs for all kinds of faces -- dolls, humans, cartoons, cats. At this early stage, any face will do. (in the graph see how the blue and green lines are overlapping at 170ms).
However, give the brain a few hundred more milliseconds and only the human faces sustain a heightened response. (in the graph, see how the blue and green lines diverge by 400ms). This tells us that once a face is detected, the brain continues to scrutinize that face for evidence of a mind. Wheatley, Weinberg, Looser, Moran, & Hajcak (2011).
These two stages of face perception -- 1) Detect all faces 2) Filter out false alarms -- is remarkably efficient. It ensures the rapid liberal face detection necessary for survival (better to false alarm to a face-like rock pattern than miss a foe) while ensuring that we do not waste precious cognitive resources on the false alarms. We may notice a mannequin but we will not waste our energy trying to read its thoughts.