Research finds that guys have trouble reading non-verbal cues and often mistake a friendly smile to mean sexual interest.

More often than not, guys interpret even friendly cues, such as a subtle smile from a gal, as a sexual come-on, and a new study discovers why: Guys are clueless.

More precisely, they are somewhat oblivious to the emotional subtleties of non-verbal cues, according to a new study of college students.

"Young men just find it difficult to tell the difference between women who are being friendly and women who are interested in something more," said lead researcher Coreen Farris of Indiana University's Department of Psychological and Brain Sciences.

This "lost in translation" phenomenon plays out in the real world, with about 70 percent of college women reporting an experience in which a guy mistook her friendliness for a sexual come-on, Farris said.

Some might think the results come down to "boys being boys," and so even the slightest female interest sparks sexual fantasy. But the study, to be detailed in the April issue of the journal Psychological Science, also found that it goes both ways for guys — they mistake females' sexual signals as friendly ones. The researchers suggest guys have trouble noticing and interpreting the subtleties of non-verbal cues, in either direction.

The study's funding came from the National Institutes of Mental Health and the National Institute on Alcohol Abuse and Alcoholism.

Flirting or not?

To unravel it all, Farris and her colleagues examined non-verbal communication in a group of 280 undergraduates, both men and women with an average age of 20 years old.

The students viewed images of women on a computer screen and had to categorize each as friendly, sexually interested, sad or rejecting. Each student reported on 280 photographs, which had been sorted previously into one of the categories based on surveys completed by different groups of students.

Overall, women categorized more images correctly than men did. When it came to friendly gestures, men were more likely than women to interpret these to mean sexual interest.

More surprising, the researchers found guys were also confused by sexual cues. When images of gals meant to show allure flashed onto the screen, male students mistook the allure as amicable signals.

So ladies trying to brush off a guy at work or the gym may need to be, uh, more direct. Men in the study also had more trouble than women distinguishing between sadness and rejection.

Programmed for sex

The results help to tease out the underlying causes of guys' flirt-or-not mistakes. One common explanation for reports of men taking a friendly gesture as "she wants me," is based on men's inherent interest in sex, which is thought to result from their biology as well as their upbringing.

Following this idea, men and women would be aware of the same behavioral cues, but men would have a lower threshold for what qualifies as sexual interest. In contrast, women would wait for compelling evidence before labeling a behavior as sexual interest.

However, Farris and her colleagues didn't find this to be the case. Rather than seeing the world through sex-colored glasses, men seemed just to have blurry vision of sorts, overall. For instance, the college guys sometimes mistook sexual advances as pal-like gestures.

"I would say that there are many factors that could relate to men demonstrating insensitivity to women's subtle non-verbal cues," said Pamela McAuslan, associate professor of psychology at the University of Michigan-Dearborn, who was not involved in the current study. These factors would include socialization, gender roles and gender stereotypes, she said.

For instance, "women are supposed to be the communicators, concerned with relationships and others … men are supposed to be less concerned with communication and to be constantly alert for sexual opportunities," McAuslan said. "This could mean that men in general may be less sensitive to subtle non-verbal behavior than women."

That doesn't mean such men can't learn to read cues or that all men are clueless decoders of women's gestures.

"These are average differences. Some men are very skilled at reading affective cues," Farris told LiveScience, "and some women find the task challenging."