Facial Expressions of Emotion Categories are Embedded within a Dimensional Space of Valence-arousal
One of the longest standing debates in the emotion sciences is whether emotions are represented as discrete categories such as happy or sad or as continuous fundamental dimensions such as valence and arousal. Theories of communication make specific predictions about the facial expression signals that would represent emotions as either discrete or dimensional messages. Here, we address this debate by testing whether facial expressions of emotion categories are embedded in a dimensional space of affective signals, leading to multiplexed communication of affective information. Using a data-driven method based on human perception, we modelled the facial expressions representing the six classic emotion categories – happy, surprise, fear, disgust, anger and sad – and those representing the dimensions of valence and arousal. We then evaluated their embedding by mapping and validating the facial expressions categories onto the valence-arousal space. Results showed that facial expressions of these six classic emotion categories formed dissociable clusters within the valence-arousal space, each located in semantically congruent regions (e.g., happy facial expressions distributed in positively valenced regions). Crucially, we further demonstrated the generalization of the embedding beyond the six classic categories, using a broader set of 19 complex emotion categories (e.g., delighted, fury, and terrified). Together, our results show that facial expressions of emotion categories comprise specific combinations of valence and arousal related face movements, suggesting a multiplexed signalling of categorical and dimensional affective information. Our results unite current theories of emotion representation to form the basis of a new framework of multiplexed communication of affective information.