“She’s pinpointing what’s kind of obvious, and yet unexplored: that women are so fluid in their sexuality,” one of the directors of “Bi the Way,” Josephine Decker, said at an after-party for the screening at a Russian-themed gay bar in Midtown.

Even in a culture that often cycles through moments of bisexual chic  Britney and Madonna, make way for Lindsay Lohan and Samantha Ronson (photographed smooching in Cannes, France)  and despite survey data showing that young people, in particular, are open to sexual experimentation, bisexuality still tends to be treated as a novelty, a titillating fluke, a phase or even a cover for homosexuality. Dr. Chivers herself was an author of a 2005 study using similar methods that found that men who called themselves bisexual were significantly more aroused by one gender, usually by men.

But women, some researchers say, are fundamentally different. A University of Utah researcher, Lisa M. Diamond, published a study in January in the journal Developmental Psychology that followed the love lives of 79 nonheterosexual women who variously labeled themselves lesbian, bisexual or none-of-the-above. Over 10 years, Dr. Diamond found, the women continued to be attracted to both sexes.

Women’s response to images of coupling extends even to other species, Dr. Chivers found. In a 2004 experiment, and again in the recent study, published in the December 2007 Journal of Personality and Social Psychology, Dr. Chivers and her colleagues found women slightly but significantly aroused by footage of bonobo chimps mating. Men showed no such response.

And when Dr. Chivers asked her subjects to rate their own arousal to the videos they watched, the women, whether gay or straight, tended to give higher ratings to films showing women. “Heterosexual women are responding to women, which is counterintuitive,” Dr. Chivers said. “Why are women so turned on by watching other women?” Straight and gay men, as well as lesbians, were more predictably aroused by images of their preferred sex, Dr. Chivers found.

It is tough to know what to make of this information. Dr. Chivers makes no bold claims for it. “To conclude that women are bisexual on the basis of their sexual responding overlooks the complexity and multidimensionality of female sexuality,” she wrote in her paper. She did allow that the apparent flexibility of women “may be related to greater potential for bisexuality in women than in men.”