What can Nature teach us about face recognition?

Peter Tu masterfully crosses face recognition technology, the Naturalistic Fallacy, and engineering in Faces, brains and prairies, oh my.

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Take a look at this animation. One face will flash; then it will be followed by another face.
How does our visual system decide if something is a face? Some automated face-detecting software uses color as one cue that something is a face. For example Apple's iPhoto has no trouble determining that there are two faces in this color picture:
Earlier today we asked readers to imagine an angry face.