The study, by a team of psychologists in Chicago and Toronto, lends support to those who have long been skeptical that bisexuality is a distinct and stable sexual orientation.
People who claim bisexuality, according to these critics, are usually homosexual, but are ambivalent about their homosexuality or simply closeted. "You're either gay, straight or lying," as some gay men have put it.
In the new study, a team of psychologists directly measured genital arousal patterns in response to images of men and women. The psychologists found that men who identified themselves as bisexual were in fact exclusively aroused by either one sex or the other, usually by other men.
The study is the largest of several small reports suggesting that the estimated 1.7 percent of men who identify themselves as bisexual show physical attraction patterns that differ substantially from their professed desires.
"Research on sexual orientation has been based almost entirely on self-reports, and this is one of the few good studies using physiological measures," said Dr. Lisa Diamond, an associate professor of psychology and gender identity at the University of Utah, who was not involved in the study.
The discrepancy between what is happening in people's minds and what is going on in their bodies, she said, presents a puzzle "that the field now has to crack, and it raises this question about what we mean when we talk about desire."
"We have assumed that everyone means the same thing," she added, "but here we have evidence that that is not the case."
Myself, I think that people are working with different definitions of bisexuality. While I know that it's a notoriously bad idea to judge the legitimacy of a scientific experiment based on a press report, the researchers seem to be working with a definition of bisexuality as a sexual orientation marked by an individual's equal attraction to individuals of both sexes. This doesn't work with the definitions of bisexuality that I've used and which seem to be fairly current, which argue that bisexuality is a sexual orientation in which people experience some attraction to individuals of both sexes and that this attraction can definitely be unbalanced. That's been my experience of bisexuality ever since the light bulb went on, at least.
Yes, I know full well that you can question whether or not I'm actually gay with a passing interest in women, and that I am quite aware that this question can be debated endlessly. I've tired of this debate. I've realized that whenever I try to inquire too deeply, I end up encountering a variation upon Heisenberg's uncertainty principle, ignorant of both my precise location (here, on the Kinsey scale) and my exact motion. I've abandoned location for, well, motion. I know my starting point well enough to be able to navigate, at least. I leave precise determinations for others.