Love at first sight seems to be attributed exclusively to face attractiveness, a study carried out by Penn University researchers suggests.

They have devised an experiment in which participants had a fraction of a second to assess a person's level of attractiveness, and the result points out to the presence of precise patterns in the brain of what we call "attractive" and to the automatic link between beautiful faces and positive traits.

"We're able to judge attractiveness with surprising speed and on the basis of very little information. It seems that pretty faces 'prime' our minds to make us more likely to associate the pretty face with a positive emotion," said Ingrid Olson, a professor in Penn's Department of Psychology.

The purpose of the tests was to study the cognitive processes behind a very real phenomenon: physically attractive people have advantages that unattractive people do not.

"Research has demonstrated time and again that there are tremendous social and economic benefits to being attractive. Attractive people are paid more, are judged more intelligent and will receive more attention in most facets of life. Studies suggest that even infants prefer pretty faces," Olson added.

The first study tested the idea that beauty can be assessed rapidly by asking study participants to rate faces - pictures of non-famous males and females taken from three different high school yearbooks and the Internet - shown for .013 seconds on a computer screen.

Although participants reported that they could not see the faces and that they were guessing on each trial, they were able to accurately rate the attractiveness of those faces.

"There are no definite rules to what kind of face can be called beautiful, but we chose faces of either extreme, very ugly or very pretty. Seen rapidly, viewers were able to make what amounted to an unconscious, albeit accurate, assessment of physical beauty," Ingrid Olson added.

The next two experiments targeted the notion of "priming", whether or not seeing a pretty face makes a viewer more likely to associate that face with positive attributes. Participants were shown a face on the screen, followed shortly after by a word in white text on a black screen. Participants were instructed to ignore the face and were timed on how quickly they could classify the word as either good or bad. Almost uniformly, response times to good words, such as "laughter" or "happiness," were faster after viewing an attractive face.