Gay? Heterosexual? It’s all in your eyes.
A new study has found that pupil dilation is an accurate indicator of sexual orientation. When people are sexually aroused by looking at pornographic images, their pupils unconsciously dilate so that they can determine sexual orientation without a genital diagnosis.
Ritch Savin-Williams, a developmental psychologist at Cornell University and the study’s lead researcher, said this is the first large-scale experiment to show that pupil dilation coincides with a person’s sexual arousal. “So if a man says he’s heterosexual, then he sees a beautiful woman and his pupils dilate.” Savin-Williams had this to say to LiveScience magazine, “Instead, it’s the gay man who sees a handsome man that gets his pupils dilated.”
The eyes know the truth
The link between pupil size and sexual arousal has been around for a long time. In 16th-century Italy, women would use eye drops derived from the poisonous herb ranunculus, which dilated their pupils and made them look sexy.
Savin-Williams says that in fact, many exciting or interesting things, such as a lover’s face or a beautiful work of art, can cause the pupils to dilate minutely. This dilation is a sign of excitement in the autonomic nervous system, which controls unconscious actions like pulsing and breathing.
Traditionally, when researchers examine sexual arousal and sexual orientation, volunteers are hooked up to instruments that measure blood flow to the genitals and watch pornographic movies or pictures. For men, the circumference of their penis is measured, while for women, a probe is used to measure pressure changes in the blood vessels of the vaginal wall. This measurement is flawed, Savin-Williams said. Some people can suppress their sexual arousal, or even have no sexual arousal response at all in a laboratory setting, so that a genital invasion diagnosis is performed to find out what’s really going on. “Some people just don’t want to be involved in research that involves their genitals,” Savin-Williams said. Savin-Williams said.
Savin-Williams said it’s not objective to simply ask if people are sexually aroused by a particular stimulus, and some people may be ashamed to admit their orientation or even deny it. And asking direct questions about sexual orientation can be difficult in many cultures.
Detecting sexual arousal
To address these questions, Savin-Williams and his Cornell University colleague, Gerulf Rieger, directed their research at the pupil. They recruited 165 men and 160 women, including gay, straight, and bisexual. These volunteers watched a one-minute video of a man masturbating, a video of a woman masturbating, and a video of a landscape. This video was brightness matched, and different lighting did not affect the results.
A pupil-tracking camera measures small changes in the pupil during the playback of these videos. Volunteers also reported how they felt after watching each video. The results showed that pupil dilation matched the sexual arousal trait. In men, this trait was usually straightforward: heterosexuals responded to female images, homosexuals to male images, and bisexuals to both men and women.
For women, Savin-Williams said, it’s not as straightforward. Gay women are similar to heterosexual men, reacting to images of other women with dilated pupils. Although reported as feeling for men, heterosexual women respond to pornographic images of both men and women.
This doesn’t mean that all heterosexual women are secretly bisexual, Savin-Williams said, just that their subjective sexual arousal doesn’t necessarily match their bodies. Sex researchers aren’t sure why that is. One theory is that because women have historically been in danger of rape, they have evolved to respond to any sexual stimulus, no matter how uninteresting it may be. The idea is that this allows women to reduce the damage during sexual assault, making it more likely that their genes will be passed on.
The researchers’ detailed findings were published in the Aug. 3 issue of PLoSONE. savin-Williams said that next, they will perform both pupil measurements and genital measurements to see how consistent their results are.
Finally, he said, the technique could be applied to sexuality research across cultures because pupil dilation is not dependent on sexual orientation, is applicable across language populations, and has generalizability. savin-Williams added that the method could even be used to help people who are unsure of their sexual orientation.