Think about some of the modern world's most iconic images. Warhol's Marilyn Monroe. Van Gogh's self-portrait. Da Vinci's Mona Lisa. What do they all have in common? The artists painted their subjects featuring the left side of their faces.

It turns out these artists were on to something. Evidently, our left side could be our best side. In a new study, researchers at Wake Forest University found that images of the left side of the face were rated and perceived as more aesthetically pleasing than those of the right side.

Our highly specialized facial muscles are able to express a multitude of distinct emotions, and we rely on them to communicate with each other. Darwin was the first to recognize the asymmetry of our facial expressions, taking note that when a person smirks only one canine tooth is typically seen. That each side of our face can essentially work independently of the other when expressing emotions also has implications for how it is observed by others.

In order to test whether there is a bias to perceive one side of the face as more aesthetically pleasing than the other, the investigators used both conscious and unconscious measures to assess participants' preferences. Participants were asked to rate the pleasantness of grey-scale photographs of real people, comprised of 10 men and 10 women displaying both sides of their faces. They were shown both the original photographs as well as mirror-reversed images so that an original right-cheek image looked like a left-cheek image and vice versa. What did the researchers find? Not only did participants rate the left side as more pleasant, but their pupil size also increased with their pleasantness ratings. Pupil dilation is an unconscious measure of interest. These findings held up despite whether the image was mirror-reversed or not.