In the recent study published in the journal of Psychological Science, twenty participants were asked to rapidly evaluate hundreds of photographs: first, of couples, and then of individuals. For each photo of the couples, they were asked to make a split-second decision about whether the couples were feeling "sexual desire" or "romantic love." With the photos of the individuals, they were asked to report how they felt toward the individual in the photo—were they marriage potential, or just sexually attractive?
Researchers didn't release any data about who was more likely to be in the "love" versus "lust" category, but they did discover through eye-tracking data that when people reported "romantic love," they locked eyes with the person in the photo. When they reported "sexual desire," their eyes wandered around the person's entire face and body.
Obviously, these conclusions come from people looking at photos of strangers—so we're reluctant to say this solves the "love at first sight" quandary. That said, you don't need eye-tracking technology to try this one out on your next date. All you have to do is follow his gaze and see: Is he looking at your eyes, or elsewhere? Just use this little tip to identify a lusty or loving fellow.