Summary: Smiles can increase, or decrease, physical stress depending on how we perceive them, researchers report.
Source: Bar Ilan University.
Sweaty palms, a racing heart, a faltering voice. Many people find public speaking unpleasant. The mere anticipation of social evaluation increases the activity of almost all body systems related to stress, with particularly strong activation in the hypothalamic-pituitary-adrenal (HPA) axis, the human body’s central stress response system.
How does the HPA axis respond to feedback we receive from others in these social situations? Positive or negative verbal feedback in response to a speech, such as “that was/wasn’t good”, is known to activate the HPA axis. But until now little scientific inquiry has been conducted into how our bodies respond to purely nonverbal feedback, such as facial expressions.
A new study of nonverbal feedback, published today in Scientific Reports by researchers from the University of Wisconsin-Madison and Bar-Ilan University, finds that smiles may reduce or increase physical stress depending upon how they are perceived. Jared D. Martin, Heather Abercrombie and Paula Niedenthal, of the University of Wisconsin-Madison, and Eva Gilboa-Schechtman, of the Department of Psychology at Bar-Ilan University, demonstrate that smiles with different social functions have different effects on HPA axis activity when they are perceived as evaluative feedback in stressful social situations.
The researchers measured cortisol levels in the saliva of 90 male undergraduate students as an indicator of HPA axis activity. They discovered that ‘dominance’ smiles, which challenge social standing and signal disapproval, were associated with higher HPA axis activity, such as increases in heart rate and salivary cortisol. Individuals perceiving ‘dominance’ smiles also took longer to return to their baseline cortisol levels after the stressful event. These physical responses to ‘dominance’ smiles mirror the influences of negative verbal feedback.
By contrast, ‘reward’ and ‘affiliation’ smiles, which reinforce behavior, signal lack of threat and facilitate or maintain social bonds, respectively, exerted influences similar to the effects of displays of friendliness and positive social evaluation and buffered physiological activity.
The authors also found that individuals with higher heart-rate variability – the variation in the time between each heart beat – showed more nuanced responses to different smiles. Higher heart-rate variability – an index of parasympathetic nervous system activity – is positively associated with facial expression recognition accuracy.
“The findings provide further evidence for the view that smiles do not necessarily constitute positive nonverbal feedback, and that they may impact social interactions by affecting the physiological reaction of people who perceive them. In addition, cortisol appears to support the detection of social threat and coordinate biological activity needed to adequately respond to the threat,” wrote the researchers. They also noted that the findings contribute to growing evidence of individual differences in sensitivity to the meaning of facial expression.
The authors caution that the small sample of exclusively male participants limits the generalizability of the findings. Further research is needed to explore if men and women respond differently to the same kind of smile, and to test the physiological effects of more overtly negative facial expressions.
[cbtabs][cbtab title=”MLA”]Bar Ilan University “Certain Smiles Aren’t All They Are Cracked Up to Be.” NeuroscienceNews. NeuroscienceNews, 4 March 2018. < https://neurosciencenews.com/hpa-smiles-8588/>.[/cbtab][cbtab title=”APA”]Bar Ilan University (2018, March 4). Certain Smiles Aren’t All They Are Cracked Up to Be. NeuroscienceNews. Retrieved March 4, 2018 from https://neurosciencenews.com/hpa-smiles-8588/[/cbtab][cbtab title=”Chicago”]Bar Ilan University “Certain Smiles Aren’t All They Are Cracked Up to Be.” https://neurosciencenews.com/hpa-smiles-8588/ (Bar Ilan Universityessed March 4, 2018).[/cbtab][/cbtabs]
Functionally distinct smiles elicit different physiological responses in an evaluative context
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.