Researchers at Northwestern University are measuring arousal rates in a sample of heterosexual women who have been exposed to pornographic material, reports The Daily Northwestern.

Prof. Michael Bailey and graduate student Meredith Chivers masterminded a test that has been designed to study if straight women react differently to straight porn and lesbian porn. They performed the experiment on a sample of 29 female Northwestern students in a Cresap lab.

They hope to show whether a woman's sexual orientation is reflected by her response to different displays of eroticism.

The 29 subjects were mostly young, heterosexual and sexually inexperienced.

Each subject is sitted in a chair with a probe about four inches long in her vagina, attached to a clear cord that dangles between her legs. She then watches video clips of penetrative and oral sex, performed by both a man and a woman, then a woman and a woman, separated by landscape scenes.

While watching the videos, her left hand is free; her right hand holds a lever that can be forced forward, like the throttle on a motorboat. As the viewer gets turned on, she pushes down on the lever. The tampon-shaped probe between her legs shines a light, and then measures how much of it is reflected back. As she gets excited, the blood starts to pulse. The dark fluid flows in and the vaginal photo-plethysmograph picks up less and less light.

The study shows that no matter the pairing, the women reacted similarly.

"It appears that women, regardless of sexual orientation, respond to everything," Bailey said.

Whilst it seems that women are aroused by straight and lesbian sex, a similar study was carried out last year to test men for their reaction to straight and gay porn. They found that straight males were not aroused by gay sex, and that gay men were not aroused by straight sex. Neither had much crossover.

Bailey has admitted that he knows sexual arousal isn't easily quantifiable and he knows that certain people might be more attracted to some actors than others. He added that his assistants tried hard to find arousing video clips that "not too cheesy."

"Hopefully, nobody was reminded of someone," Bailey said.