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Study shows eyes are the windows to sexual orientation

It sounds impossible: to tell whether someone is gay or straight. But science says you can do it just by looking at the eyes.

Written by Laura Shin, Contributor Aug. 9, 2012 at 8:00 p.m. PT

Ah, if only "gaydar" were as scientific as it sounds.

But since it's not (and is instead based on completely unreliable stereotypes), science keeps looking to improve on it, such as a new study which claims that the secret to detecting a person's sexual orientation is in the pupils.

Basically, a person's pupils dilate when looking at someone they find attractive. Based on this premise, the researchers have created an experiment that vastly improves upon previous sexual orientation tests, which relied on invasive genital monitoring.

While testing by looking at the eyes is an improvement, the test has its own limitations: you can't conduct the pupil measurements with the naked eye.

Why previous experiments were faulty

This study shows that the way previous researchers had been going about it wasn't getting the best results.

Usually, researchers would ask study participants to watch erotic movies or look at such pictures while instruments measured blood flow to their genitals. For men, the circumference of their penis was measured, and women would be monitored with a probe that measures pressures changes in the blood vessels of the vaginal walls.

But Ritch Savin-Williams, the developmental psychologist at Cornell University who conducted this latest experiment said that some people don't have genital responses in a lab environment or they can suppress their arousal.

Also, he added, "Some people just don't want to be involved in research that involves their genitals," Savin-Williams said. (Gee, wonder why?)

Other experiments that simply asked a person if he or she was aroused were also problematic, because some people may not admit their own desires, and in certain cultures, such questions were not easy to ask.

How the latest study differed

The premise of his study, however, was based on the fact that pupils dilate in response to any stimulus a person finds exciting or interesting. So, even a beautiful art work or your sister's face will cause this involuntary response in your eyes, much the way your body involuntarily breathes.

Savin-Williams and his colleague Gerulf Rieger, also of Cornell University, gathered 165 male and 160 female participants of all sexual orientations. The volunteers watched one-minute videos: one of a man masturbating, one of a woman masturbating and the last of neutral landscape scenes. The brightness of the videos was kept constant so that it wouldn't affect the dilation of their pupils.

A gaze-tracking camera recorded changes in pupil size while these participants watched the videos, and the researchers also asked them to report their own feelings of arousal to each video.

The results in this study matched the pattern seen in previous genital arousal studies: Straight men respond to sexual imagery of women, bisexual women to images of both sexes and gay men to images of men.

In women things are a bit different: The pupils of gay women dilate more when they see images of other women, but straight women's pupils dilate equally when shown erotic images of both sexes, even if they report feelings of arousal only for men and not women.

(This effect has been seen in other experiments, and the reasons aren't exactly clear. One theory is that because women throughout history have been at risk of rape, their bodies would prepare physically by responding to any sexual stimulus, even if it was unappealing.)

The benefit of this new method of detecting sexuality, which Savin-Williams said could be used to help people who are confused about their sexuality, is that it could be used in cross-cultural studies of sexuality. Hey -- anything that does away with experiments that measure genital arousal in a lab environment sounds like an improvement in science.