Sex almost always gets people's attention -- whether they are consciously aware of it or not.
Some people think about it all the time: Fifty-four percent of men and 19 percent of women think about sex every day or several times a day, according to the Kinsey Institute for Research in Sex, Gender and Reproduction.
Now scientists say that some people react to erotic images that they can't even see. A study released today in the journal Proceedings of the National Academy of Sciences reports that subliminal erotic images compete for the brain's attention even if those images are hidden from our eyes.
Researchers also found an interesting connection between a people's sexual orientation and how their brain reacted to each picture. It seems that subjects were more distracted by subliminal images of the gender they found more sexually desirable.
For example, heterosexual women are attuned to images of naked men but not to images of naked women, the researchers found after analyzing their data. Homosexual men are attuned to images of naked men, and homosexual women were equally distracted by naked images of both sexes.
But this research has not convinced experts in human sexuality to jump to any conclusions about sexual orientation.
"The concept of a test to determine sexual orientation is anywhere between reductive and ludicrous," said Cory Silverberg, a sex educator and sexual media consultant in Toronto.
"Neither the medical science nor the social science community has come anywhere near producing a body of work that could concretely define something like sexual orientation."
So, these data are less about sex and more about our subconscious and how the brain reacts to subliminal information.
The idea that the brain reacts to subliminal information isn't terribly surprising -- the advertising industry has exploited this for decades. The brain can process what cannot be seen, such as subliminal presentations of erotic, violent or other emotional stimuli. But the scientists did not know whether the brain can act on this invisible information.
Researchers from the University of Minnesota wanted to see how powerfully subliminal images could affect our ability to pay attention.
Scientists gave 40 men and women a visual attention test while flashing subliminal erotic images or neutral images -- a pixilated scrambled image -- as a distracter. Scientists wanted to see how the images affected men's and women's test scores.
The erotic image was rendered "invisible" by a technique called interocular suppression. The subliminal erotic image flashed at the same time as a neutral image, on either side of a single focus point. So if the subliminal erotic image flashed on the left side of a focal point, the neutral image flashed on the right side of that point.
The visual attention task began after the erotic and neutral images disappeared.
Scientists quickly flashed a test picture of parallel lines on either the left or right side of that same focal point. They then asked the study subjects to recall on which side of the focal point the picture had appeared.