Perception of basic emotion blends from facial expressions of virtual characters: pure, mixed, or complex?

As animated virtual characters in games, movies and other applications become more humanlike, it becomes more and more important to be able to imitate the complicated facial behaviour of a real human. So far, facial expression animation and research have been dominated by the basic emotions view, limited to the six universal expressions: anger, disgust, fear, joy, sadness and surprise. More complex facial expressions can be created by blending these basic emotions, but it is not clear how these blends are perceived. Are they still perceived as basic emotions or combinations of basic emotions, or are they perceived as expressions of more complex emotions? We used a series of online questionnaires to study the perception of all pairwise blends of basic emotions. The blends were produced as a sum of facial muscle activations in the two basic emotions, using a physically-based, animated face model. Our main finding is that several basic emotion blends with an opposite valence are perceived as complex emotions that are neither pure emotions nor their blends. Blends of basic emotions with a similar valence are typically perceived as pure basic emotions (e.g., a blend of anger and disgust is perceived as pure anger). Only one of the blends (joy+surprise) was perceived as a blend of two different basic emotions.