It all boils down to your relationship status, suggest Florida State University (FSU) psychology researchers including Jon Maner, PhD.
People who are in relationships don't do that, since they're not looking for a mate. But they warily watch very attractive people of the same sex because they may poach their mate, Maner's team observes.
Those habits happen in the blink of an eye, flying under the radar of the conscious mind, the researchers report in September's Journal of Personality and Social Psychology.
Can't Look Away
"If we're interested in finding a mate, our attention gets quickly and automatically stuck on attractive members of the opposite sex," Maner says in a news release.
"If we're jealous and worried about our partner cheating on us, attention quickly and automatically gets stuck on attractive people of our own sex because they are our competitors," he adds.
"These kinds of attentional biases can occur completely outside our conscious awareness," Maner says.
In a series of experiments, Maner's team showed pictures of people ranging from "very unattractive" to "very attractive" to 442 heterosexual FSU undergraduates.
The students watched the photos pop up, one by one, on a computer screen. Each picture was displayed for a split second, followed by a square or circle that sometimes showed up on another part of the screen.
The students were told to press a computer key, as quickly as possible, to indicate whether they saw a circle or square. They also completed questionnaires about their relationships.
When the photo had shown a very attractive person, the students were slower to look away from the spot on the screen where that photo had been.
Single people only did that after seeing photos of very attractive people of the opposite sex. The researchers call that a "mate-search" phenomenon.
People in relationships only lingered after seeing photos of very attractive people of the same sex. Maner's team calls that "mate-guarding" behavior, which was particularly strong among jealous people.
The study doesn't show whether people actually act on those instant visual impulses. But the findings may help explain the visual snare of physical attractiveness.
(What is the first thing to attract you to the opposite sex? Talk about it on WebMD's Sexuality: Friends Talking message board.)