Narrator: This is Science Today. During the course of a half-hour conversation, it's not uncommon for a person to make up to 300 different facial expressions. But Paul Ekman, a psychology professor at the University of California, San Francisco, says the three most common facial expressions are non-enjoyment and enjoyment smiles and the raising of eyebrows. Ekman is a leading researcher of facial expressions.
Ekman: We developed a technique almost twenty-five years ago for measuring precisely movement off of videotape or film. It allows us to specify which muscles have moved and therefore, whether we're seeing an enjoyment smile or a non-enjoyment smile. Some of the research that we've done is to look at the difference in brain activity.
Narrator: Ekman's interest is to be able to index and understand momentary changes in emotion.
Ekman: And the face is still the best technique we have for doing that. The voice isn't bad, but people aren't always speaking, so you can't do the equivalent of not speaking with your face. It's always talking, if you like, and so it's a very good source of information.
Narrator: For Science Today, I'm Larissa Branin.