Dynamic signaling of facial expressions transmit social information in a hierarchical manner over time
62.28, Wednesday, May 15, 10:45 am - 12:45 pm, Royal Ballroom 4-5
RACHAEL JACK1, 2, OLIVER GARROD1, PHILIPPE SCHYNS1; 1Institute of Neuroscience and Psychology (INP), University of Glasgow, United Kingdom, G12 8QB, 2School of Psychology, University of Glasgow
Designed by both biological (Susskind et al., 2008; Andrew, 1963) and social evolutionary pressures (Darwin, 1999/1872), facial expressions transmit specific sequences of information across time to achieve an optimal system of social signaling and decoding (Darwin, 1999/1872; Schyns et al., 2009). Here, we show for the first time that this dynamic signaling transmits social information over time in a hierarchical manner that fits evolutionary pressures. We proceeded in two steps. First, we used 4-dimensional (3-dimensional face over time) reverse correlation to reconstruct the dynamic mental models of the 6 basic facial expressions of emotion, for 60 Western Caucasian observers individually (Yu et al., 2012; Jack et al., 2012. See Figure S1, Panel A). Second, from the distribution of mental models, we constructed a 6-choice Bayesian classifier (see Bayesian Classifiers in Supplementary Material) that accrues Action Unit (AUs; Ekman et al., 1972) signals over time, as a function of their availability. Analyses revealed that early facial signalling leads to systematic confusions (p<.01. See Figure S1, Panel B, pink boxes) between fear and surprise (and also disgust and anger), due to specific shared AUs (eye lid raiser and nose wrinkler, respectively. See Figure S1, Panel C, pink boxes). Accurate discrimination of each one of the six basic emotions is delayed by the later availability of diagnostic AUs (e.g., eye brow raiser and upper lip raiser, respectively. See Figure S1, Panel C, green boxes). We conclude that the face transmits social signals in a hierarchical manner that fits evolutionary pressures: Initially, the eye lid raiser and the nose wrinkler signal two types of danger (Susskind et al., 2008; Lee et al., in press; Chapman et al., 2009), which, with the addition of diagnostic AUs, are distinguished further into the six basic emotions (e.g., surprise) and their subtypes (e.g., positive vs. negative surprise).