Is he gay? See if his eyes dilate when he watches men on screen.
New Study Says You Can Tell Sexual Orientation From the Eyes

By Diane Anderson-Minshall

Originally published on Advocate.com August 05 2012 2:27 PM ET

Add this to your gaydar: a new report in Live Science says that you can tell a person's sexual orientation from their eyes. Pupils, that is. According to Stephanie Pappas, a new study finds that pupil dilation is an accurate indicator of sexual orientation. When people look at erotic images and become aroused, their pupils open up in an unconscious reaction, which gave researchers a much easier way to to study orientation and arousal without traditionally invasive blood flow to the genital measurements.

Researcher Ritch Savin-Williams, a developmental psychologist at Cornell University, says the new study is the first large-scale experiment to show that pupil dilation matches what people report feeling aroused by.

"So if a man says he's straight, his eyes are dilating towards women," Savin-Williams told LiveScience. "And the opposite with gay men, their eyes are dilating to men."

Savin-Willims told Live Science that the pupils dilate slightly in response to any exciting or interesting stimulus, a sign that the autonomic nervous system — the system that controls involuntary actions like pulse and breathing — is ramping up.

Savin-Williams and fellow researcher Gerulf Rieger had 325 men and women who idetified as gay, straight, or bisexual watch one-minute videos of a man masturbating, a woman masturbating, and neutral landscape scenes while a camera measured tiny changes in their pupil sizes.

The results, according to Live Science, showed that pupil dilation matches the pattern seen in genital arousal studies. In men, this pattern is generally straightforward: Straight men respond to sexual images of women; gay men to sexual images of men; and bisexual men to both men and women. But women's responses were more complex, said Savin-Wiliams, because while lesbians responded to images of other women, straight women "dilate basically equally in response to erotic images of both sexes, despite reporting feelings of arousal for men and not women."

Whether there's a host of closeted bisexual women or another evolutionary answer to this straight girl dilation, it gives researchers a complex result to try to unravel.

To read the full study, visit Live Science.