By Alice Park, Time
Distinct facial muscles were used to express compound emotions
Leading scientific thinkers of their time, such as Aristotle, Rene Descartes, Guillaume Duchenne, and Charles Darwin, have long promoted the idea that there are a handful of basic emotions that people express. In recent decades, that group has crystalized into six core emotions: happiness, surprise, sadness, anger, fear, and disgust.
But there are clearly many shades of gray between those emotions. For example, there’s the happy-because-I’m-eating-ice cream and the happy-because-I-just-learned-I-got-a-surprise-marriage-proposal looks, each of which is slightly different.
That’s what intrigued Aleix Martinez, associate professor of electrical and computer engineering at Ohio State University. “Six seemed a small number given the rainbow of possibilities of feeling and expressing emotions,” he says.
Martinez wanted to know whether compound emotions, such as happy surprise, were expressed using the same muscle movements of both happiness and surprise, or whether the expression involved a unique set of muscles that represented some amalgam of the two.
What he and his colleagues found was that the human face makes 21 different emotional expressions – and each is different from the other. While some represented combinations of emotions, each differed in terms of which muscles were involved.
And surprisingly, these facial expression patterns were remarkably consistent across all 230 volunteers. For example, each showed happy surprise in the same way that was distinct from both happiness and from surprise, and different still from angry surprise.
Martinez broke down the facial expressions of 230 volunteers by applying his engineering strategies. He and his colleagues gave each of the students, staff, or faculty members who enrolled in the study different scenarios and asked them to show how they would react in each one. They were told, for example, that they had just learned they had been accepted to a graduate program, that someone had told them a disgusting, but still funny joke, or that they had just smelled something bad. The volunteers were allowed to practice their facial expressions in front of a mirror before Martinez took pictures of their reactions.
He then computer-analyzed each of the 5,000 images, breaking them down by which facial muscles the participants used. These were first defined in 1978 by psychologist Paul Ekman, who codified facial expressions in the Facial Action Coding System (FACS) by action units, or muscles or groups of muscles that went into making facial expressions – such as lip parts (for showing disgust), showing teeth (for expressing happiness), mouth stretch (for fear), or eyelid tightening (for anger).
Feature continues here: Human Faces