The Cornell Chronicle explains:
Pupils were found to widen most when study participants watched erotic videos of people they found attractive, thereby revealing where they were on the sexual spectrum from heterosexual to homosexual.
Although there was a popular belief that sexual orientation can be revealed by pupil dilation to attractive people, there was no scientific evidence until now. For the first time, researchers at Cornell used a specialized infrared lens to measure pupillary changes to participants watching erotic videos.
An interesting finding from the study revealed that “flexible sexual desire” is not only found in women.
“We can now finally argue that a flexible sexual desire is not simply restricted to women — some men have it, too, and it is reflected in their pupils,” says Savin-Williams. “In fact, not even a division into ‘straight,’ ‘bi,’ and ‘gay’ tells the full story. Men who identity as ‘mostly straight’ really exist both in their identity and their pupil response; they are more aroused to males than straight men, but much less so than both bisexual and gay men.”
As researchers expected heterosexual men showed “strong pupillary responses” to the women they saw on-screen, but women responded to both sexes, which, according to researchers, confirms that women have a different sexuality than men.
So, the next time you meet someone and you’re not sure they’re feeling you, check their pupils. They just might tell you if the person’s feeling you or not.