Just how can someone accurately predict a person's sexuality basedon a fleeting glimpse of a photograph?
But the new research from the University of Washington may shed some light. The researchers suggest that gaydar is a complex mental process that involves not only identifying particular facial features, but also those features' configurations and relationships to one another.
The research appears in this week's journal of the Public Library of Science.
We all make snap judgments several times a day, every day, when encountering strangers.
"We call it intuition," said Nicholas Rule, a psychology researcher at the University of Toronto, who was not involved with this study. "When you get on a subway car and have only a split second to figure out who you're going to sit next to, you're using those first impressions."
And according to scientists, we're actually pretty good at making accurate snap judgments.
There are the obvious ones, such as telling the difference between a man and a woman, or gauging a person's race or ethnicity, or assessing someone's economic status.
But according to Rule and others' research, we also can tell Mormons from non-Mormons (apparently, Mormons have healthier-looking skin), Democrats from Republicans (Democrats look kinder, Republicans more dominant), and we can apparently predict – based on high school photos – how long someone is going to live (something to do with impulsivity).
Sexual orientation is another area people have an ability to detect, the Public Library of Science article states.
In this latest research, Joshua Tabak at the University of Washington and his co-author, Vivian Zayas at Cornell University, tested the ability of college students to judge sexual orientation.
They collected photos from Facebook in which the target had identified himself or herself as gay or straight. In order to make sure that there were no "clues" or extra-physical "giveaways," they excluded photographs in which people were wearing obvious makeup or glasses, had visible piercings or sported facial hair.
They then showed the photographs to the college students. But they let the students see each photo for only 50 milliseconds, which is about a third of the time it takes for a person to blink.
The researchers found that the students were better at guessing a person's sexual orientation than you'd expect by chance. They also found that it was easier for the students to peg a woman's sexual orientation – they did this 64 percent of the time accurately – than a man's – which was around 57 percent of the time.
But in order to figure out how the students were making their snap judgments, the researchers turned some of the photos upside down.
According to Tabak, researchers have been unclear as to whether particular facial features – such as the eyes, nose or mouth – are the telltale sign or if it's how the features are configured on the face – such as the distance between the eyes or the orientation of the lips relative to the chin.
Psychologists know that we have specific neurons that are used when assessing these configurations. However, if you turn a photograph upside down, these neurons don't fire. They become useless.
Tabak found that the students still could tell sexual orientation when a photograph was turned upside down, but their accuracy decreased. He said this indicated that we're using both feature assessment and configuration and that we use configuration to enhance our snap judgments of sexuality.
Both he and Rule said this kind of research, while interesting, could also have policy implications. The reality of gaydar, they say, undercuts arguments and laws, such as "Don't Ask, Don't Tell," that rely on the premise that if sexuality is kept a secret, it will eliminate homophobia.
Others, however, say this kind of research has no place in policy discussions and might instead serve anti-gay agendas.
Aaron Belkin, director of the Los Angeles-based Palm Center, an advocacy group for LGBT members in the armed services, said he was "almost" offended by the research and was skeptical that it had any policy implications.
"Whether or not people's perceptions about the sexual orientation of another are accurate, the need for anti-discrimination legislation is just as urgent," Belkin said. "You can have an inaccurate perception and still discriminate."
Being able to pinpoint someone's sexual identity by physicality "does not necessarily have any effectiveness on laws designed to protect" groups of people who might be discriminated against, said Belkin, who is also an associate professor of political science at San Francisco State University.
Belkin also pointed out that there is no way of knowing in this experiment whether some of those people photographed were gay and calling themselves straight.
Both Belkin and Cathy Renna, a gay-rights advocate and managing partner of Renna Communications, said this kind of research implicitly condones stereotyping, even if that is not the intent.
"It's so interesting because it plays into the idea that there are stereotypes that exist because there are commonalities in certain groups of people that pop up," Renna said. "But there are always those, maybe a majority, that don't fit those stereotypes."
"It's like, what's the point?" she said. "There's real harm that can happen when we allow people to make assumptions. The reality is it is very easy to stay in the closet and not have people know you are LGBT. There are thousands upon thousands of people who have done it for years and decades."
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