At Cornell, my eyes told a different story. In the small eye-tracking testing room, I watched a series of clips of men and women masturbating. Rieger told me that for most men, their pupil dilation is a strong predictor of their sexual identity. But my professed identity (mostly gay) didn’t match my pupil response. “You dilated almost twice as much as a regular gay man and almost as much as a regular straight man to women,” Rieger told me. “Your pupils actually tell me that you’re more bi than gay.”

That was news to me. I felt a sudden kinship with the self-described bisexual men in Bailey’s original 2005 study, who must have been surprised to learn that they had their sexual orientation all wrong. I could imagine a potentially awkward scenario the next time someone asked me if I was into men or women. “Well, now, that depends on whether you believe the sex researchers at Northwestern or Cornell,” I might have to say.

Rieger’s suggestion did throw me for a momentary loop. Might I actually be bisexual? Have I been so wedded to my gay identity — one I adopted in college and announced with great fanfare to family and friends — that I haven’t allowed myself to experience another part of myself? In some ways, even asking those questions is anathema to many gays and lesbians. That kind of publicly shared uncertainty is catnip to the Christian Right and to the scientifically dubious, psychologically damaging ex-gay movement it helped spawn. As out gay men and lesbians, after all, we’re supposed to be sure — we’re supposed to be “born this way.” It’s a politically important position (one that’s helping us achieve marriage equality and other rights), but it leaves little space for out gay men to muddy the waters with talk of Kinsey 4s and 5s.

Bisexuality, too, is politically problematic. Are bisexuals born bisexual? Where does choice come into the picture? John Sylla’s longtime partner, Mike Szymanski, told me that his parents didn’t accept his bisexual identity. “If you’re born that way and you can’t choose, that’s something we can accept, but if you like both, then you do have a choice,” Szymanski’s mother told him.

Unlike Szymanski, I don’t believe I’m bisexual — no matter what my pupils suggest. It doesn’t feel true as a sexual orientation, nor does it feel right as my identity. And though I don’t discount the value of studying arousal in a lab setting, I spoke to several bisexual activists who did. Sexuality, they told me, is far too complex to be quantified by our reaction to pornography. “Sure, sexual orientation is partly about our response to visual stimuli,” Robyn Ochs told me. “But it’s about other sensory inputs too. And it’s about our emotional response. Sexuality is so complex, and I worry that valuable funding dollars are going to studies that don’t actually really tell us all that much about bisexuality.”

To their credit, both Rieger and Savin-Williams were thoughtful in their conversations with me about the challenges of studying bisexuality. Savin-Williams, in particular, said he was mostly interested in understanding the “incredible diversity” among bisexuals. He told me about one young man he interviewed whose arousal looked “extraordinarily gay” in the lab. But he was romantically interested in only women. “He falls madly in love with girls all over the place,” Savin-Williams said, “and it’s not because he hates the ‘gay’ part of himself. He just connects romantically and emotionally with women in a way he doesn’t with men. Will that change? Perhaps. But right now he’s not 50-50 interested in men and women — it’s almost like he’s 100 percent and 100 percent, but in two different ways. Most of the time sexual attraction and romantic attraction will overlap, but for some bisexual people, there’s a discrepancy between the two.”

Rieger nodded. “People constantly surprise you,” he said, recalling one young man who announced that he was “50-50 bisexual” but who only showed arousal to women in the lab. “His arousal was like a perfect straight guy,” Rieger told me.