In March, a study in Archives of Sexual Behavior reported the results of a different approach to the question. As in the Northwestern study, the researchers showed participants erotic videos of two men and two women and monitored genital as well as subjective arousal. But they also included scenes of a man having sex with both a woman and another man, on the theory that these might appeal to bisexual men.

The researchers — Jerome Cerny, a retired psychology professor at Indiana State University, and Erick Janssen, a senior scientist at the Kinsey Institute — found that bisexual men were more likely than heterosexuals or gay men to experience both genital and subjective arousal while watching these videos.

Dr. Lisa Diamond, a psychology professor at the University of Utah and an expert on sexual orientation, said that the two new studies, taken together, represented a significant step toward demonstrating that bisexual men do have specific arousal patterns.

“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,” she said. “These converging lines of evidence, using different methods and stimuli, give us the scientific confidence to say this is something real.”

The new studies are relatively small in size, making it hard to draw generalities, especially since bisexual men may have varying levels of sexual, romantic and emotional attraction to partners of either sex. And of course the studies reveal nothing about patterns of arousal among bisexual women. The Northwestern study included 100 men, closely split among bisexuals, heterosexuals and homosexuals. The study in Archives of Sexual Behavior included 59 participants, among them 13 bisexuals.

The new Northwestern study was financed in part by the American Institute of Bisexuality, a group that promotes research and education regarding bisexuality. Still, advocates expressed mixed feelings about the research.

Jim Larsen, 53, a chairman of the Bisexual Organizing Project, a Minnesota-based advocacy group, said the findings could help bisexuals still struggling to accept themselves.