It has long been suggested that it is possible to tell whether someone is sexually attracted to another by the dilation of the pupils. Researchers have taken this a step further and have completed a study, published in PLoS One in August 2012, which claims that it is possible to tell a person’s sexual orientation by looking at his or her pupils. Interestingly though, women’s responses were found to be different from men’s.
As ABC News reports, the researchers, from America’s Cornell University, used an infrared lens to measure the “pupillary changes” of participants in the study while they watched erotic movies. In the majority of cases, researchers were then able to determine which gender the participants found most attractive, which usually matched the individual’s stated sexual preference. 325 participants took part in the study, of whom 165 were men and 160 were women. They were between the age of 20 and 35 and all were willing to share information on their sexual orientation.
This kind of study has been carried out in the past, but involved genital monitoring, which is obviously found very invasive by a lot of people. For men, that involves a rubber band around the penis, while for women, an instrument to measure blood flow is inserted into the vagina. Pupil dilation is therefore a much less intrusive way of monitoring sexual arousal.
The results from the male participants were most straightforward; heterosexual men’s pupils dilated when they watched videos of women and homosexual men’s pupils dilated when they watched videos of men. Women, on the other hand, showed pupillary changes whether looking at erotic videos of men or women. Although the reason for this needs more investigation, it is believed that it is not that women are secretly bisexual, but rather that they have a different kind of sexuality; as an article in the Daily Mail puts it, “their subjective arousal doesn't necessarily match their body's arousal.”
Psychcentral.com explains that the most interesting part of the study is the pupillary changes in bisexual men. The presumption was previously that bisexual men were more likely to base their choice of sexual partner on “physiological sexual arousal but on romantic and identity issues” and that they would therefore not have much in the way of pupillary change. That proved not to be the case however; bisexual men were found to have substantial changes whether watching videos of men or women, showing that it isn’t just women who have flexible responses to sexual stimulation.
Despite the role that pupil dilation can apparently play in determining sexual orientation, research participants may apparently still need to undergo genital monitoring. The Daily Mail claims that the next phase of the research will involve a simultaneous measurement of both the pupils and the genitals.