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How To...Interpret Facial Expressions

Photo by Christina Gandolfo

A team of folks from the MIT Media Lab and tech company Affectiva is studying the nuances of the human face. The goal: develop education products for people with autism spectrum disorders. Here, Affectiva shares some truths about smiles.

1. Researchers classify expressions based on muscle groups. An insincere smile uses the lip-corner pullers, which are voluntary muscles. A sincere smile also involves the cheek raisers and eye crinklers, which are involuntary.

2. Most people—90%, in fact—smile when they're frustrated, and these smiles of frustration have the same physical characteristics as happy smiles.

3. But happy smiles linger longer: After filling out a buggy online form, frustrated study participants smiled for just 7.5 seconds on average. When they watched a video of a baby laughing, smile time jumped to an average of 13.8 seconds.

More "How To":

NEXT: How to...Say You're Running Late

A version of this article appeared in the February 2013 issue of Fast Company magazine.