There are three distinct types of smile, a new study has revealed. People switch between 'reward', 'affiliation' and 'dominance' smiles, using different facial muscle combinations to make them, according to researchers from the University of Wisconsin-Madison.
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It's claimed the findings could enable people to influence the outcome games and negotiations and could even assist surgeons working on facial reconstructions.
"When distinguishing among smiles, both scientists and laypeople have tended to focus on true and false smiles," said Paula Niedenthal, a psychology professor at the University of Wisconsin-Madison. "The belief is that if you smile when you're not happy, the smile is false. But people smile in many different circumstances and during many emotional states. So asserting that only smiles that result from states of happiness are 'true' smiles limits our understanding of this important facial expression."
The 'reward smile' is the most intuitive, according to the research team, which also included members from Cardiff University and the University of Glasgow. This is "the kind of smile you would use with a baby, so he will smile back or do things you like", says Niedenthal. It involves a symmetrical hoist of the zygomaticus – the facial muscle below the cheekbone that pulls the corners of the mouth into a grin - plus a dash of eyebrow.
The second type of grin is the 'affiliative smile', which is used to communicate tolerance, acknowledgment or a bond and to appear unthreatening, according to the study. This involves a similar symmetrical upturn of the mouth, but spread wider and thinner with pressed lips and no teeth exposed.
Completing the trio is the 'dominance smile', which the study says is used to signify status in social hierarchies. This is where the symmetry disappears, and the smile turns into more of a lopsided sneer. Confusingly, it's paired with the raised eyebrows and lifted cheeks usually associated with expressing enjoyment.
Participants in the study, published in the journal Psychological Science, looked at thousands of computer-generated expressions that used random combinations of facial muscles, but each one included some action from the zygomaticus - or the 'smile muscle'. They were then asked to say whether each was a reward or affiliative or a dominance smile, or not a smile at all. The participant-sorted smiles were then shown to two more sets of observers so that the researchers could whittle down 'recipes' for each type of grin.
"We now know which movements we should look for when we describe smiles from real life," said Magdalena Rychlowska from Cardiff University. "We can treat smiles as a set of mathematical parameters, create models of people using different types of smiles, and use them in new studies."
The researchers are already working with surgeons who repair and reconstruct facial bones and muscles. "They may have to make choices that will affect a patient's expression for the rest of their life," said Niedenthal. "It's useful for them to know how different kinds of smiles are used in the world, and which muscles are involved in making them."
The results could also help to improve intercultural communication, as the smiles used can vary between countries and cultures.
This article was originally published by WIRED UK
