Vagueness in the wild: how do we decide what is and isn't a face?

Vagueness is a philosophical problem that continues to generate discussion, especially in formal epistemology. But the question of how we deal with vague information in the wild remains a largely unexplored empirical domain. When do we decide, for example, whether or not something is a face? As Guthrie (1993, Faces in the clouds) pointed out, humans are prone to detect faces in such objects like clouds, rock formations, and plugs. Jesus' face is regularly discovered in a slice of pizza or a fishstick. Guthrie speculated it is evolutionary advantageous for us to see more faces (more agency in general) than is warranted - we err on the side of caution. But clearly, unless we are delusional, we don't see faces everywhere. Not every passing cloud is interpreted as a face. So the question is: how does our mind decide what is and isn't a face?

Meng and colleagues, in a paper that recently appeared in the ahead of print papers of the Proceedings of the Royal Society B, have offered interesting empirical evidence that may shed light on the problem of vagueness in the real world. They showed participants carefully designed visual stimuli that ranged from nonfaces to faces and used fMRI to examine neural responses. They found a division of labor: the left fusiform gyrus, a brain area long known to be involved in face processing, calibrated the face properties of each visual stimulus in a graded manner (more activity when the stimulus is more face-like), whereas the right fusiform gyrus made a quick categorical decision on whether or not the image was a face (only activation if the subject thought the stimulus was a face). In other words: the left hemisphere assigns a rank of how facelike a stimulus is, but does not decide whether or not the stimulus is a face or not. The categorization only takes place in the right hemisphere which presumably takes its input from the left (the activation in the left hemisphere precedes that in the right by a few seconds as well, confirming the hypothesis that the right hemisphere receives its input from the left).  Intriguingly, face-selectivity persists in the right hemisphere, even after activity in the left has subsided. Followup studies will examine the functionality of face recognition in blind children who have recently had their sight restored.