Each movement is categorized in Action Unit (AUs). When you puff your cheeks, it's known as AU13. The Frontalis muscle, located on the forehead, is responsible for AU1 or the "Inner Brow Raiser". Over the course of their extensive research, Ekman and Friesen determined that there are at least 19 different versions of smiles! For more information and additional resources on FACS, visit the Data Face website.

If you live in the Bay Area, you can see a special exhibit at San Francisco's Exploratorium with more of Dr. Ekman's photos. It's open through May 11.

Watch the "Emotions Revealed" TV Story online, as well as find additional links and resources.

Jenny Oh is an Associate Producer for QUEST on KQED Television.

See if you can tell from the 2 images below:*

A real, spontaneous smile incorporates tiny muscles around the eye that are nearly impossible to contract at will. You can see this for yourself in an exhibit called "Polite Smile, Delight Smile" part of the Exploratorium's new Mind exhibition.

This corners-of-the-eyes giveaway, as well as many other subtle, yet revealing, facial gestures, was discovered by Paul Ekman, now a professor emeritus of psychology from the University of California, San Francisco. Ekman's been studying the universality of facial expressions and the secrets our faces reveal for over four decades. The notion that certain expressions of emotion are programmed into us wasn't so well received when he proposed it in the 1960s. At that time, social scientists believed facial expressions were cultural. Then, in 1967, Ekman embarked on an expedition to Papua New Guinea, where he asked people belonging to an indigenous tribe that had virtually no contact with the developed world to imitate the expressions they would have in certain situations, such as meeting an old friend or discovering a decaying animal. Ekman found that the ways these people's faces expressed sadness, fear, surprise, anger, and disgust involved the same eye and mouth muscle movements that people from Western cultures displayed. The collection of photos he took there will be on display at the Exploratorium from January 22 –April 27, 2008.

Today, Ekman is lauded by psychologists. He's considered the leading expert on detecting deceit, and his ideas are used to train CIA, Homeland Security, and other law enforcement officers to detect when they are being lied to by someone they're questioning and to spot unusual behavior. He devised a tool known as the Facial Action Coding System (FACS), which catalogues the musculature behind thousands of facial expressions. Some of the most subtle of these Ekman calls "microexpressions," fleeting muscle movements that reveal emotions the subject is trying to suppress. With the knowledge that these revealing expressions are universal, FACS allows a trained person to "read" someone's emotions by observing their facial muscles.

When Ekman's book Emotions Revealed came out in 2003, I thought it would be great to master the subject matter. Who wouldn't benefit from learning to understand the fleeting messages people send oh-so-subtly? But the more I thought about it, the more uneasy I began to feel. Something didn't sit right with me about the practice of decoding people without their knowledge. Then again, isn't that what any of us do when we "sense" that someone was nervous or untruthful or secretly overjoyed? It's not like our microexpressions are hidden. We express them in plain sight. They may be the source of an intuitive person's "sixth sense." But to formally study these expressions with the intent of detecting emotions that the subjects themselves are unaware of–is that a violation of privacy? Ekman would say no. He insists that he can't read minds, only emotions, and that leaves out most of the personal details. Still, there's something unsettling about the idea that feelings I've long considered private are written all over my face.

* BTW, the real smile is image 1. Did you guess correctly? Leave a comment to tell us how you knew.

Robin Marks is a journalist and science writer who current serves as a Multimedia Projects Developer for the Exploratorium in San Francisco, CA.

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