An important aspect of emotion perception that has been overlooked concerns the difference between the continuous nature of the sensory inputs that people receive and the categorical nature of their thinking about emotion. In facial expressions, the contractions of various facial muscles can vary continuously to create gradations of movements (Jack & Schyns, 2015). But people typically talk about these expressions in categorical terms, calling them expressions of “fear” or “calm,” for instance (Barrett, 2006).Whether we think about emotions continuously or categorically does have some important ramifications. A nuanced view of emotion can make us better at detecting how others are feeling, while thinking about them in categories means that a facial expression or behavior has to reach some threshold before we decide the other person is feeling a certain emotion. This would in turn impact our behavior and interactions with others. It might also impact how we manage our emotions. Viewing emotions continuously also allows us to understand more complex emotions, made up of combinations of the basic emotions. According to Ekman, there are 7 basic emotions:
They conducted two studies, in which participants examined pictures portraying emotions while undergoing MRI. In the first study, participants saw faces displaying fear or calm to varying degrees, and either categorized them or marked where they fell on a continuum for "fear" and "calm." In the second study, participants judged their own responses to graphic images, either as categorically "bad" or "neutral" or along a continuum. They found different levels of activation in parts of the brain responsible for emotion, specifically the amygdala and the insular cortex (the part of the cerebral cortex closest to the amygdala and other structures in what is known as the midbrain):
Activation was greater when the perceived intensity of the negative emotion was greater. When people were only given categories to work with, they had to force pictures into those holes, even when the displayed emotion wasn't very extreme. So a picture showing very mild fear that a participant categorized as fearful produced greater activation in those parts of the brain. Activation was lower when the perceived intensity of the positive or neutral emotion was greater. Allowing a "gray area," through use of a continuum, would allow for more accurate perception, while being forced to use categories may change perception, leading people to perceive the target as being more similar to the category selected. Obviously, this goes beyond emotions, and could have some important implications for other work involving categories, such as stereotypes.