In the past these studies measured genital arousal, an invasive procedure not everyone would want to submit to. It caused particular problems measuring the sexual response of those too young, old, or conservative to submit to typical sex research.

The new test is simpler and less invasive. Scientists show subjects erotic videos, and measure how their pupils dilate in response.

Some of the findings confirm the expected. Straight men’s pupils responded to sexual images of women, and barely responded to images of men. Straight women’s pupils responded to both, confirming Lisa Diamond’s theory that women’s sexuality is more fluid than men’s.

The most interesting finding was confirmation of the existence of male bisexuality. Contrary to previous physiological studies, bisexual men in this study had pupil dilation in response to both male and female images.

According to our pupillary responses, bisexuality exists.

Summary:

• Straight Women: Pupil dilations in response to both erotic male and female images.
• Gay Women: Pupil dilations in response to erotic female images.
• Straight Men: Pupil dilations in response to erotic female images.
• Gay Men: Pupil dilations in response to erotic male images.
• Bisexual Men: Pupil dilations in response to both erotic male and female images.

Source:

• Rieger G, Savin-Williams RC (2012) The Eyes Have It: Sex and Sexual Orientation Differences in Pupil Dilation Patterns. PLoS ONE 7(8): e40256. doi:10.1371/journal.pone.0040256