Your best side may be your left cheek, according to a new study by Kelsey Blackburn and James Schirillo from Wake Forest University in the US. Their work shows that images of the left side of the face are perceived and rated as more pleasant than pictures of the right side of the face, possibly due to the fact that we present a greater intensity of emotion on the left side of our face. Their work is published online in Springer's journal Experimental Brain Research.Others can judge human emotions in large part from facial expressions. Our highly specialized facial muscles are capable of expressing many unique emotions. Research suggests that the left side of the face is more intense and active during emotional expression. It is also noteworthy that Western artists' portraits predominantly present subjects' left profile.Blackburn and Schirillo investigated whether there are differences in the perception of the left and right sides of the face in real-life photographs of individuals.The authors explain: "Our results suggest that posers' left cheeks tend to exhibit a greater intensity of emotion, which observers find more aesthetically pleasing. Our findings provide support for a number of concepts – the notions of lateralized emotion and right hemispheric dominance with the right side of the brain controlling the left side of the face during emotional expression."Participants were asked to rate the pleasantness of both sides of male and female faces on gray-scale photographs. The researchers presented both original photographs and mirror-reversed images, so that an original right-cheek image appeared to be a left-cheek image and vice versa.They found a strong preference for left-sided portraits, regardless of whether the pictures were originally taken of the left side, or mirror-reversed. The left side of the face was rated as more aesthetically pleasing for both male and female posers.These aesthetic preferences were also confirmed by measurements of pupil size, a reliable unconscious measurement of interest. Indeed, pupils dilate in response to more interesting stimuli – here more pleasant-looking faces, and constrict when looking at unpleasant images. In the experiment, pupil size increased with pleasantness ratings.Blackburn K & Schirillo J (2012). Emotive hemispheric differences measured in real-life portraits using pupil diameter and subjective aesthetic preferences. Experimental Brain Research; DOI 10.1007/s00221-012-3091-y