[MUSIC] One of the most expressive areas of the human body is the face, which is the area most closely observed during any interpersonal communication. That's why, although it's more convenient to chat with our friends online or even over the phone, it's never as satisfactory as seeing them face to face. And when we want to share important news with our close friends and family, for instance when we got a new job or getting married. We still much prefer to do it in person so we can really share the happiness together. We use our face to express emotions. In fact, a face is capable of producing about 20,000 different facial expressions. However, two strangers, even from completely different backgrounds, are still able to distinguish certain emotions from the face of each other. Psychologists have been trying to select a set of emotional facial expressions and define them as basic emotions, which are universally recognized. The most famous approach came from Paul Ekman in 1969, where he defined six basic emotions as universal. Happy, surprise, fear, anger, disgust, and sad. Each basic emotion has their distinguished facial features. For instance, for surprise, someone will have their eyes wide open, eyebrows raised, and mouth slightly open. And for someone who is angry, they will have their eyes squint, eyebrows down and together, and mouth tightly closed. In order to describe the facial movements of these emotional facial expressions, we often use a system called facial action coding system, or FACS. Originally published in 1978, this system describes individual facial movements such as cheek raiser and lip corner puller as action units. You can add action units together to create different expressions. For instance, if I add cheek raiser and lip corner puller, I will create the emotional facial expression, happy. We can also assign intensity of each unit to express different intensity of emotions. Or a mixture of intensity of different action units to create different expressions. Other than expressing emotions, facial expressions play another important role in our face to face interaction. That is, communicative acts. In other words, we use our facial expression to supplement our verbal exchange in conversations. For instance, if when I talk, I keep my face completely neutral, this becomes very boring, very quickly. But if I move my facial muscles and my head a little bit according to what I say, then I become a lot more interesting and would sound a lot more convincing. We display communicative facial expressions not only when talking, but also when listening. This is part of the reasons why it's always easier to explain things face-to-face to someone. Because you can have a real-time feedback of how much the information they understand. And if they are interested or bored with your explanation, so you can adjust your communication style accordingly. Again, it's hard to define a fixed set of communicative acts, as there are many and they would differ from culture to culture. And they will be influenced by many other factors, including personality, the interpersonal relationship between the two persons talking. A basic set of communicative acts used while listening could be agree, disagree, interested, concentrate, thinking, and uncertainty. Different from emotional expressions, communicative acts have more dynamics when being expressed. We often need a little video clip rather than just a single image to recognize if someone is agreeing or disagreeing, interested or uncertain. Also, in order to express those expressions, we often need to animate not only the face but also head movements. For instance, nodding for agreement and shaking for disagreement. [MUSIC]
