A new study with the potential for considerable controversy, finds little physiological evidence for bisexuality in men. Psychological investigations into bisexuality in the past have mostly been based on self-report measures - this is one of the first to directly measure physiological arousal.

In this study a sensor was attached to the penis and participants were shown erotic films, some involving just men and some involving just women. Having been asked about their sexuality before the experiment, patterns of arousal were compared with the stated preferences. Arousal was as expected for those identifying themselves as heterosexual and homosexual,

"But the men in the study who described themselves as bisexual did not have patterns of arousal that were consistent with their stated attraction to men and to women. Instead, about three-quarters of the group had arousal patterns identical to those of gay men; the rest were indistinguishable from heterosexuals."

The researchers are, quite rightly, extremely cautious about the implications of their study which is based on a fairly small sample (101). It is unclear what the relationship is between physiological arousal and emotional and cognitive factors.

Certainly Freud believed that humans were naturally bisexual and the sex researcher, Alfred Kinsey, found evidence from the thousands of interviews he conducted that most people had at least some attraction to both sexes. This kind of research flies in the face of conventional thinking on the subject - part of the reason it's so interesting.

As for bisexual women, the NY Times goes on to report that, unlike bisexual men, other research has shown that those women identifying themselves as bisexuals have shown physiological arousal to both men and women. From this evidence the physiological case for bisexuality looks stronger in women than in men.
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