When it comes to what turns them on, women are either bisexual or gay, but rarely straight, according to a new study by the University of Essex.

Whereas previous research has shown that women generally are sexually aroused by both men and women to varying degrees, it overlooked the differences between women who are straight or gay.

This latest research from Essex, published in the Journal of Personality and Social Psychology, for the first time clearly defines the differences between straight and gay women. Using both eye tracking devices and direct measures of physiological sexual response, the study, which involved 345 women, found that straight women were strongly sexually aroused to videos of both attractive men and attractive women, even though they reported that they are only interested in men.

This was in contrast to lesbians who showed much stronger sexual responses to their preferred sex (women) over their less preferred sex (men). It shows that lesbians are more male-typical in their arousal than straight women, as it is usually men who show distinct sexual responses to their favourite sex. The researchers also tested the theory that because lesbians can be more masculine in many of their non-sexual behaviours, that they are also more masculine in their sexual responses. However, the research, led by Dr Gerulf Rieger, did not find any evidence that the most masculine-behaving lesbians showed the most male-typical sexual arousal patterns.

“Although some lesbians were more masculine in their sexual arousal, and others were more masculine in their behaviours, there was no indication that these were the same women,” explained Dr Rieger, from the Department of Psychology. “This shows us that how women appear in public does not mean that we know anything about their sexual role preferences. Men are simple, but women’s sexual responses remain a mystery.”

Earlier this year research by Dr Rieger showed that pupil dilation and sexual arousal are 100 per cent linked. A new eye-tracking laboratory has been built at Essex to help develop new methods of understanding and testing sexuality which are less invasive and, therefore, more likely to attract a broader and more diverse range of participants.