Beyond Darwin: revealing culture-specificities in the temporal dynamics of 4D facial expressions.

Since Darwin’s seminal work on the evolutionary and biological origins of facial expressions, the Universality Hypothesis maintains that all humans express six basic emotions - "happy," "surprise," "fear," "disgust," "anger" and "sad" - using the same set of distinct facial movements. Testing this hypothesis directly, we used a novel platform to generate random 3-dimensional facial movements, which observers perceive as expressive when correlating with their mental representations. Fifteen Western Caucasian (WC) and 15 East Asian (EA) observers each categorized 4,800 (same and other race) animations according to the six basic emotions (or "don’t know") and by intensity ("very low" to "very high." Figure S1, Panel A). We then reverse correlated the random facial movements with the emotion responses they elicited, thus computing 180 models per culture (15 observers x 6 emotions x 2 race of face). Each model comprised a 41-dimensional vector coding the facial muscle composition and temporal dynamics. The Universality Hypothesis predicts that these models will form six distinct clusters (one per emotion) in each culture and show similar signaling of emotional intensity across cultures. We show cultural divergence on both counts: Cluster analysis of the models in each culture revealed that WC models optimally form 6 distinct and emotionally homogenous clusters as predicted (Levenson 2011), whereas EA models overlap between emotion categories, with little categorical structure (Figure S1, Panels B-C). Cross-cultural comparison of emotional intensity signaling across time (i.e., co-variation of facial movements and intensity) revealed further cultural differences. Whereas WC models signal emotional intensity with distributed face regions, EA models showed early signaling with the eyes, as mirrored by popular culture EA emoticons -- (^.^) "happy" and (O.O) "surprise." Here, we refute the Universality Hypothesis and raise the question: if the 6 basic emotions are not universal, which emotions are basic in different cultures