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.