Washington: Left side images of the face are rated as more aesthetically pleasing than that of its right side, possibly because the left cheek reflects greater emotional intensity, says a study conducted by the Wake Forest University in the US.

Kelsey Blackburn and James Schirillo of the university investigated whether there were differences in the perception of the left and right sides of the face in actual photographs of people.

The results suggested that posers' left cheeks tended to exhibit a greater intensity of emotion, which observers found more aesthetically pleasing, say Blackburn and Schirillo in the "Experimental Brain Research" journal.

The participants were asked to rate the pleasantness of both sides of male and female faces on gray-scale photographs. 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.