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Bisexual men won’t likely be surprised — or feel particularly validated — to learn that a new scientific study confirms that their sexual attraction to both men and women is real. But the findings may help enlighten those who still subscribe to the stereotype that bisexual men are just closeted homosexuals, or simply confused.

For the new study, researchers at Northwestern University recruited a group of 100 Chicago-area men, identifying as heterosexual, homosexual or bisexual in roughly equal numbers. Unlike a previous Northwestern study of bisexuality, however, the current study used more stringent criteria to define bisexuality.

Bisexual men were required to have had sexual encounters with at least two people of each gender and to have been in at least one romantic relationship of three months or longer with a person of each gender. The previous study, published in 2005, largely relied on responses to a standard questionnaire to determine sexual orientation.

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The participants were hooked up to genital sensors that measured erectile arousal while they watched videos of male or female same-sex intimacy. The men were also asked to rate their subjective arousal in response to the videos on a scale of 0 to 10.

The researchers found that bisexual men reported being aroused by both types of videos and that the genital sensors also measured arousal to both. Gay and straight men in the study did not have the same responses.

By contrast, the 2005 study had suggested that bisexual men’s responses of arousal and attraction resembled those of homosexuals. The New York Times’ David Tuller reported:

That conclusion outraged bisexual men and women, who said it appeared to support a stereotype of bisexual men as closeted homosexuals.

“I’ve interviewed a lot of individuals about how invalidating it is when their own family members think they’re confused or going through a stage or in denial,” Dr. Lisa Diamond, a psychology professor at the University of Utah who was not involved with the study, told the Times.

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Still, Dr. Diamond and others interviewed by the Times noted that measuring genital arousal to erotic videos in the lab doesn’t reveal much about real-world sexual encounters — or about a person’s sexual orientation and identity. Indeed, the parameters for inclusion in the study were perhaps more telling of the actual bisexual experience.

“This unfortunately reduces sexuality and relationships to just sexual stimulation,” Ellyn Ruthstrom, president of the Bisexual Resource Center in Boston, told Tuller. “Researchers want to fit bi attraction into a little box — you have to be exactly the same, attracted to men and women, and you’re bisexual. That’s nonsense. What I love is that people express their bisexuality in so many different ways.”

The new study was published online by the journal Biological Psychology.

Meredith Melnick is a reporter at TIME. Find her on Twitter at @MeredithCM. You can also continue the discussion on TIME’s Facebook page and on Twitter at @TIME.