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Jonas Nölle, Chaona Chen, Laura B. Hensel, Oliver G. B. Garrod, Philippe G. Schyns, Rachael E. Jack; Facial expressions of emotion include iconic signals of rejection and acceptance. Journal of Vision 2021;21(9):2932. doi: https://doi.org/10.1167/jov.21.9.2932.
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© ARVO (1962-2015); The Authors (2016-present)
What are the evolutionary origins of facial expressions? One theory posits that they evolved from facial movements that control sensory stimulation (e.g., closing eyes to reduce visual input). Such signals would afford a salient iconicity that could facilitate communication. Here, we examined whether facial expressions of emotion include expansion and contraction facial movements that serve as icons of rejection and acceptance. Using the data-driven method of reverse correlation, we first modelled dynamic facial expressions of the six classic emotions – happy, surprise, fear, disgust, anger and sad – in each of 60 participants (Western, 31 females). On each of 2400 experimental trials, participants categorized a facial animation comprising a randomly activated subset of individual facial movements (Action Units; AUs) according to the six classic emotions or ‘other.’ We then modelled the dynamic AUs associated with each participant’s emotion response using non-parametric permutation inference (p < 0.05), resulting in 360 dynamic facial expression models (60 participants X 6 emotions). Next, we identified in each facial expression model, iconic facial movements and found that expansion movements – e.g., brow raising (AU1-2), eye opening (AU5), nostril dilating (AU38) and mouth gaping (AU26) – are primarily associated with acceptance messages (e.g., happy, surprise). Contraction movements – e.g., brow lowering (AU4), wincing (AU7), nose wrinkling (AU9), lip pinching (AU23) – are primarily associated with rejection messages (e.g., fear, disgust, anger, sad). Finally, we replicated these results with a separate set of facial expressions of conversational messages – thinking, interested, bored and confused (20 Westerners, 10 females). Together, our results show that facial expressions comprise latent iconic facial signals that represent rejection or acceptance in line with their social function. Future research will address how this iconicity could be exapted to ground more complex and abstract meanings in multimodal face-to-face communication.
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