Abstract
Smiles are frequently used in daily social interactions, primarily to communicate positive affect (e.g., Niedenthal, 2010). Emerging evidence now suggests that smiles can communicate a wider variety of social messages, including dominance (e.g., Rychlowska et al., 2017) and embarrassment (Keltner, 1995), with different meanings across cultures (e.g., Tsai et al., 2018). Yet, the versatility of smiles has not been systematically investigated, limiting knowledge of this frequently used facial expression. We address this question by examining how five different smile-related facial movements—Lip Corner Puller, Lip Corner Puller Left/Right, Lips Part-Lip Corner Puller, Lip Corner Puller-Cheek Raiser—elicit the perception of +100 different social messages in two cultures (Western European, East Asian) using the psychophysical method of reverse correlation and information-theoretic statistical tools. On each experimental trial, participants viewed a random combination of individual facial movements (called Action Units—AUs) and categorized the facial animation according to an emotion label if appropriate, otherwise selecting ‘other.’ Each participant (54 Western European, 59 East Asian) completed 3,600 such trials (see Jack et al., 2012; Jack et al., 2016; Chen et al., 2017). To identify the social messages that each smile AU is associated with, we measured the statistical relationship between the AUs presented on each trial and each participant’s responses using Mutual Information (Ince et al., 2017). Results revealed the versatility of smiles—in both cultures, bilateral smiles (AU12) are primarily associated with positive social messages whereas unilateral smiles (AU12L/R) and open-mouth smiles (AU25-12) are valence-versatile with the latter associated with high arousal. Further, smiles with squeezed eyes (AU12-6) are associated with positive messages in East Asian culture and valence-versatile in Western culture. Our results demonstrate the versatility of smiles as tools for social communication, thereby advancing knowledge of human facial expression communication and identifying potential sources of cross-cultural confusion.