Sheng He, a cognitive neuroscientist, had groups of 10 heterosexual men and women each and 10 homosexual men and 10 homosexual women view erotic pictures directly -- then canceled out vision of the nude image by giving one eye a highly-contrasted image called a Garbo patch, Scientific America.com reported.

The researchers found sexual orientation often determined how the brain reacts to erotic images. Heterosexual women, for example, were more subconsciously tuned in to pictures of naked men, the same reaction exhibited by homosexual men. But homosexual women were equally attuned to naked images of both sexes, a paper in the Oct. 23 issue of the journal Proceedings of the National Academy of Sciences said.

Sheng He said "it appears that our minds are exquisitely tuned to detect sexual opportunity - especially when it is invisible."

Researchers at the University of Chicago reported in 1994 that 54 percent of men and 19 percent of women admitted they think about sex every day -- or several times a day.