Cognitive neuroscientist Sheng He of the University of Minnesota and his colleagues gathered groups of heterosexual men, heterosexual women, homosexual men and bisexual women numbering 10 each. Each viewed special images pointed directly at each individual eye. The researchers could cancel out vision of one eye's image by presenting a specific high contrast image to the other eye. Such an image, called a Gabor patch, consists of a series of contrasting lines that form an abstract--and visually arresting--shape. "Normally, the two eyes look at the same image. They don¿t have any conflict," he explains. "We create a situation where the two eyes are presented with two images, and then they will have binocular competition. One image is high contrast [and dynamic], the other is static. You basically just see the dynamic image."
Into the canceled out image slot, the researchers slipped an erotic image; for example, a naked woman displayed for a heterosexual man. To ensure that subjects did not consciously detect the invisible image, they were asked to press a specific key if they noticed any difference between the left and right images. Over the course of 32 trials, men were significantly better at detecting the orientation of Gabor patches when they appeared in the slot formerly occupied by an invisible image of a nude woman.
The heterosexual men, however, had a more difficult time detecting the same orientation when it was located where an invisible picture of a nude man had been; this was not the case for heterosexual women when viewing their own sex naked. And the homosexual men¿s response was similar to that of the heterosexual women, as were the bisexual women¿s and heterosexual men¿s. This focus benefit did not carry over, however, when the participants were allowed to consciously see the naked photos, the researchers report in the paper published online in Proceedings of the National Academy of Sciences USA. It may have been that the erotic images were on display too long, they speculate; previous studies have shown that it is difficult to maintain attention in one spot. Or it could be that social or cultural norms take over. "Maybe you don't want to look at the nude pictures," he suggests. Regardless, it appears that our minds are exquisitely tuned to detect sexual opportunity--especially when it is invisible.