San Francisco State University psychologist David Matsumoto explains the science behind an athlete's "victory stance." (San Francisco State University)

The Olympics is a laboratory for testing the limits of human strength and endurance. But it serves as a laboratory for other types of experiments, too.

One such experiment has been helping researchers to unlock the mystery of facial expressions. Psychologists have long debated whether the smiles, frowns and other expressions that people make are a universal reaction that humans are born with, or whether we learn them from those around us. If we are born with certain facial expressions, researchers argue, these expressions should be the same around the world. If these behaviors are learned, though, they might differ from place to place.

For decades, researchers have believed that people in different cultures display emotions in different ways — for example, people in one culture amplify their excitement to fit in with those around them, while those in another culture learn to mask their sadness or disappointment in public. Yet some psychologists have also argued, somewhat controversially, that certain facial expressions are universal, just a part of being human. Unfortunately, researchers have found this extremely difficult to study in the lab, since it’s hard to provoke authentic and strong emotional responses in people in such an artificial environment.

Not so at the Olympics. Athletes toil and sweat for years for sometimes just a few minutes of performance on the Olympic stage, and the winners and losers of various events can’t help but let their joy, anger, surprise, frustration or disappointment at their performance shine. Just look, for example, at the surprise and delight of Chinese swimmer Fu Yuanhui when she found out from a reporter that she had won a bronze medal in the women’s 100-meter backstroke — a reaction that has made her an Internet sensation.

That has made the Olympics the ideal place for David Matsumoto, a psychologist at San Francisco State University and former Olympic judo coach, to study emotional expressions. In a series of well-known studies, Matsumoto looked at the faces of winning and losing athletes to investigate how universal human emotions are.

In one study, published in 2009 in the journal Psychological Science, Matsumoto and two co-authors examined the facial expressions of 84 judo athletes from 35 countries who competed in the 2004 Olympics Games in Athens. The photographs were taken at a rate of eight frames per second to trace how athletes’ facial expressions changed as they learned of the match’s outcome and in the minutes that followed. The stakes were high: The matches the researchers looked at were either gold-medal judo matches — in which the winner would get a gold medal and the loser would get a silver — or bronze-medal matches, in which the winner received a bronze and the loser received no medal.

Examining the photos, the researchers found evidence that facial expressions are both universal and culturally specific. In the moments after the athlete won or lost, they made facial expressions of joy, disappointment, surprise and other emotions that were remarkably consistent across countries and cultures. But as the seconds ticked by and the athletes realized they were on the world stage with many cameras pointed at them, their expressions changed in ways that did vary by culture.

"Everyone has the first immediate reaction, but if you watch a second later, they then remember I’m on stage, I’m on TV, I’ve got to be a good winner, a good loser, and everyone modulates their expressions in a certain way," says Matsumoto. "And how they modulate it, that’s entirely dependent on your culture and your upbringing."

Matsumoto emphasizes that people's behaviors are highly influenced by their individual personalities. But culture also appears to play a prominent role.

Their research found that those subsequent expressions differed based on the country’s population density, affluence and individualism. Athletes from countries with more individualistic attitudes, such as the United States, tended to be more expressive, as were those from countries with high population densities. Athletes from more rural and more collectivistic cultures tended to mask their emotions more — for example, replacing expressions of disappointment with a polite smile.

Katie Ledecky, Maya DiRado, Leah Smith and Allison Schmitt of the United States celebrate winning a gold medal. (Marcos Brindicci/Reuters)

Allison Schmitt, Leah Smith, Maya DiRado and Katie Ledecky celebrate their gold medals during the women's 4 x 200-meter freestyle relay medals ceremony. (Martin Meissner/AP)

In another study published in 2009, Matsumoto and a co-author used some of these same photos to explore those initial emotional reactions. This time, they compared the facial expressions of the judo athletes at the 2004 Summer Olympics with the expressions of blind judo athletes who were competing at the 2004 Paralympic Games. About half of these athletes were congenitally blind, meaning they had been blind from birth. The researchers reasoned that those who had been blind their entire lives were unlikely to have learned certain facial expressions from those around them.

The researchers looked at more than 4,800 photographs taken immediately after the athletes had won or lost competitions, during the medal ceremony, and on the podium. Though they were from more than 20 different countries, the sighted and blind athletes produced exactly the same kind of expressions of anger, sadness, contempt, surprise and happiness, according to the study. And there was no difference between those who had been blind from birth and those who had lost their sight as kids or adults.

Matsumoto notes that sighted and blind athletes from all different cultures adopted a specific expression and posture of triumph when they won. Matsumoto describes "the triumph expression" in the video below as a combination of "expansion, aggression and attention," in which the body expands, posture straightens, the arms raise, and the person stares fiercely at the competition or the audience.

Matsumoto says this kind of triumphant behavior is common not only among blind and sighted athletes from many different cultures, but even among animals that have won contests. This suggests that it may be an evolutionary adaptation that is somewhat biologically innate to humans. The purpose is likely to establish who's on top in a particular social order by calling attention to that individual's victory, says Matsomoto. "It is part of how that individual and how that group establishes social hierarchy."

Matsumoto's findings echo the results of another famous study by psychologists Victoria Medvec, Scott Madey and Thomas Gilovich at the 1992 Summer Olympics in Barcelona. The researchers had undergraduates examine and rate the facial expressions of the athletes on a 10-point scale ranging from “agony” at 1 to “ecstasy” at 10. To some people’s surprise, immediately after results were announced, silver medalists scored 4.8 on that scale, well below the bronze medalists at 7.1. At the medal ceremony later that day, the silver medalists had fallen to a 4.3, still below the bronze medalists at 5.7.

The reason, as Shankar Vedantam notes in an interview with Matsumoto on NPR’s Hidden Brain, has to do with the alternative that silver and bronze medalists were confronting in their competition. The silver medalists had just missed out on a gold medal — like Ukraine's Oleg Verniaiev below, who lost out on the gold medal in the men's gymnastics individual all-around — while the bronze medalists were likely happy to have received a medal at all, like Jessica Fox of Australia below. "Getting a silver at the Olympic Games is an amazing accomplishment, but silver medalists are not very happy people all the time," says Matsumoto.

Ukraine's Oleg Verniaiev reacts after seeing the score for his final round that placed him in the silver medal category on Aug. 10 during the artistic gymnastics men's individual all-around final at the Summer Olympics in Rio de Janeiro. (Julio Cortez/AP)

Jessica Fox of Australia shows off her bronze medal for the kayak K1 women's canoe slalom event at the Summer Olympics in Rio de Janeiro on Aug. 11. (Robert F. Bukaty/AP)

Matsumoto and his colleagues also observed that silver medalists and other athletes who had not performed as well as they hoped “managed” their expressions in similar ways. Those who had lost in gold- or bronze-medal judo matches often displayed polite expressions during the medal ceremony that Matsumoto calls “social smiles” — smiles in which only the corners of a person’s mouth turns up. Winners of gold and bronze medals were much more likely to show a true smile, in which the whole cheeks rise and the eyes narrow.

As a judo coach, Matsumoto has been present for four Olympic Games now. He says the backrooms at the Olympic Games are incredibly emotional places to be "because more people have lost. There's a lot of anger and tears there."

The viewing public on TV, meanwhile, typically sees only the tears and the celebration of the winners, he says.

"The rules for the winners are they can show that on TV, they can show that in public. Whereas the losers have to be good losers in public."

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