Functionally distinct smiles elicit different physiological responses in an evaluative context

Abstract

When people are being evaluated, their whole body responds. Verbal feedback causes robust activation in the hypothalamic-pituitary-adrenal (HPA) axis. What about nonverbal evaluative feedback? Recent discoveries about the social functions of facial expression have documented three morphologically distinct smiles, which serve the functions of reinforcement, social smoothing, and social challenge. In the present study, participants saw instances of one of three smile types from an evaluator during a modified social stress test. We find evidence in support of the claim that functionally different smiles are sufficient to augment or dampen HPA axis activity. We also find that responses to the meanings of smiles as evaluative feedback are more differentiated in individuals with higher baseline high-frequency heart rate variability (HF-HRV), which is associated with facial expression recognition accuracy. The differentiation is especially evident in response to smiles that are more ambiguous in context. Findings suggest that facial expressions have deep physiological implications and that smiles regulate the social world in a highly nuanced fashion.

Dynamics Matter: Recognition of Reward, Affiliative, and Dominance Smiles From Dynamic vs. Static Displays

“…The present research used continuous confidence ratings that were not mutually exclusive, thus replicating their findings with human-realistic stimuli and a different response format. Moreover, a closer inspection of participants’ ratings reveals that, whereas affiliative smiles were relatively unlikely to be classified as reward, reward smiles were often judged as affiliative, consistently with the results of Rychlowska et al (2017) and Martin et al (2018) . While this finding suggests that reward smiles – similarly to the Duchenne smiles previously described in the literature – may constitute a more homogeneous, less variable category than other smiles (e.g., Frank et al, 1993 ), it also highlights similarities between reward and affiliative smiles which both convey positive social motivations.…”

“…Instead of using computer-generated faces as done by Rychlowska et al (2017) , we employed static images and dynamic videos of human actors displaying the three types of smiles. Our experiment extends previous research ( Rychlowska et al, 2017 ; Martin et al, 2018 ) in three ways by testing (1) how accurately naïve observers can discriminate between the three functional smiles, (2) whether the capacity to classify these smiles is affected by facial muscle restriction that prevents mimicry responses, and (3) whether the type of display (static vs. dynamic) influences smile recognition, thereby moderating the potential effects of muscle restriction. In line with previous findings ( Rychlowska et al, 2017 ), we predict that observers should be able to accurately classify the three functional smiles, with affiliative smiles being more ambiguous than reward and dominance smiles.…”

“…The only context given in the study was the definition of the three smile types including examples of situations in which they might potentially occur. Recent work by Martin et al (2018) suggests that the three types of smiles elicit distinct physiological responses when presented in a social-evaluative context. Adding social context to these displays therefore provides a promising avenue for future research, as the salience of specific interpersonal tasks could facilitate the distinction between affiliative smiles and the other two categories.…”

“…Stimuli were retrieved from a set developed by Martin et al (2018) and featured eight White actors (four female) in frontal view, expressing the three smile types: reward smile (eight stimuli), affiliative smile (eight stimuli), and dominance (six stimuli) smile. Actors posed each smile type after being coached about its form and accompanying social motivations (see Martin et al, 2017 ; Rychlowska et al, 2017 ).…”

Towards a social functional account of laughter: Acoustic features convey reward, affiliation, and dominance

“…Supporting empirical work has identified the unique morphological features of the three smiles [ 9 ]. Further, validation studies have confirmed that the expressions are spontaneously categorized as smiles, and convey the distinct meanings of reward, affiliation, and dominance [ 10 ].…”