Carl Zimmer recently reviewed studies by Dr. Niedenthal in the New York Times. In it, he reports a new theory on how a person detects different types of smiles. When we see someone smile, we tend to mimic the smile. This act of mimicry lights up different parts of our brain for different types of smiles (genuine, happy, fake, etc). Dr. Niedenthal’s model suggests we decode other’s smiles by analyzing our own brain activity when we mimic.
When subjects were shown fake and genuine smiles under two conditions, with and without pencils in their mouths, those who had their smile-muscles occupied by a pencil had a significantly harder time distinguishing the test smiles. It is good support for the model, but this is still a budding field.
via The New York Times