By Stephanie Pappas
LiveScience

How a man's gaze roams over a woman's body can tell you how into sex he is — a new finding that doesn't play out when the genders are swapped.

Men's gaze reflects their underlying sexual motivation, the researchers found. A woman's gaze, on the other hand, does not seem to match her sexual thoughts as clearly.

The findings aren't just about the differences between Mars and Venus; researchers hope they can be used to track the sexual motivations of sex offenders, providing a way to measure how well treatments are working.

"Eye movement is spontaneous and very difficult to inhibit so we thought perhaps we can use an eye tracker as a reliable marker to track sexual interest," study researcher Kun Guo, a psychologist at the University of Lincoln in the United Kingdom, told LiveScience.

The eyes have it
Previous work has found that men, especially, give away their sexual thoughts with their eyes. The dilation of the pupil in response to sexual images, for example, can reveal sexual orientation reliably in men and in gay women, though straight women don't show such clear patterns. Studies have also found that heterosexual men gaze longer at pictures of women than of men, while heterosexual women look at male and female images about equally. [ 50 Sultry Facts About Sex ]

Guo and his colleagues had previously discovered when young men look at images of women close to them in age, their eyes are drawn to the chest and waist-hip region. (This may not shock any woman who's been ogled in a bar lately.) These two regions are likely important signals for men, with breasts hinting at the sexual maturity of the woman and waist/hip ratio suggesting her ability to carry a child, Guo said. Men don't show the same ogling patterns when looking at older women or children, suggesting this sizing-up may be a signal of sexual interest.

To test the idea, the researchers showed 30 men, ages 18 to 25, and an equivalent group of women, all heterosexual, pictures of clothed children, early-20s adults and adults in their late 30s or early 40s. They asked the participants to simply look at the pictures as they'd normally scan an image while a gaze-tracking device recorded where their eyes moved.

Next, the participants filled out questionnaires about their sexual personalities, covering topics from how sexually inhibited they were to how sexually compulsive, or likely to take sexual risks, they were.

Sexual gaze
By comparing the questionnaire answers with the gaze-tracking data, the researchers found that men who reported more sexual compulsivity or risk-taking gazed longer than other men at the breasts and hip-waist regions of 20-year-old women — but not at those regions in girls or women older than themselves. In other words, their gaze seems to give away their higher-than-average sexual interest. And the longer gazes are confined to women they find sexually interesting (based on age).

"We argue it's a high-level mental process which guides this unique gaze pattern," Guo said.

Women's gaze patterns were not nearly so neat. The researchers did find that highly sexually compulsive women looked more at the bodies of the 20-year-old women than did other women, but they also looked more at the bodies of children and 40-year-old women. It could be that the more sexually compulsive a woman is, the more she compares her body with other women's, the researchers wrote online Nov. 13 in the Journal of Sex Research. Either way, the women's gaze did not appear to reveal their sexual interests; no gaze patterns were found when shown images of men.

Guo and his colleagues are now analyzing the data from a third experiment comparing the gaze patterns of sex offenders with non-offenders. So far, he said, the results look promising.

"We argue probably we can use this eye tracker potentially as some kind of reliable methodologically to asses how effective the treatment is and how likely people will be to reoffend," Guo said.

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