New research helps explain how we make snap judgments about a person's sexual orientation — an ability popularly known as "gaydar."

Previous research by Nicholas Rule, PhD, at the University of Toronto, showed that people can gauge sexual orientation with better-than-chance accuracy after a quick glance at a facial photograph, and that some gaydar cues seem to be found in the mouth and eye areas. Now, in a paper published in PLoS ONE in May, Joshua Tabak, PhD, at the University of Washington, and Vivian Zayas, PhD, at Cornell University, have gone a step further toward explaining how the process works.

Tabak and Zayas showed volunteers facial photos of men and women who had indicated a preference for either same-sex or opposite-sex partners. The photographs were standardized to black-and-white, subjects were free of makeup, tattoos, piercings and eyeglasses, and hairstyles had been digitally removed. Volunteers saw each photo for 50 milliseconds and correctly judged sexual orientation about 60 percent of the time. Viewing the photos when they were turned upside down reduced accuracy, but judgments of upside-down faces were still better than chance.

That's significant, Tabak says, since we process faces in two distinct ways. Featural processing registers individual characteristics, like a nose or a lip. Configural processing focuses on spatial relationships, such as the distance between the eyes.

"When faces are upside-down, configural face processing is dramatically inhibited," Tabak says. The reduced-but-above-chance accuracy when viewing flipped faces therefore suggests that both configural and featural processing play a role in gaydar judgments.

It's still not clear why some people seem to have better gaydar than others, or precisely how facial features correlate with sexual orientation. But this study adds to the understanding of first impressions. "Even before someone says something," Zayas says, "the world is responding based on things like how you look and sound."

—Kirsten Weir