When viewing faces people report the left side of the face to be more expressive than the right, according to a study recently published in Brain and Cognition.

Facial expressions are mostly controlled by an area of the brain known as the premotor cortex which sends signals to other parts of the brain. Control of the lower two thirds of the face is contralateral, meaning that the right hemisphere controls the left side of the face and the left hemisphere has control of the right side of the face. The right hemisphere of the brain is reported to be more involved in emotion processing compared to the left, leading to greater emotional expression being displayed on the left side of the face.

It has been reported that when posing for a portrait or photograph, as humans we prefer to turn so that our left side is being offered, this effect is seen across males and females. One explanation for this is that humans instinctively know that their left side expresses more emotion. This phenomenon is known as the ‘left cheek bias’.

Although it is understood that the left side of the face is more expressive, little is known about what characteristics of the face cause us to perceive more emotion.

The study conducted by Jia Low and Annukka Lindell (La Trobe University, Melbourne) aimed to uncover whether configural (arrangement of facial features) or featural information results in the left cheek bias when processing facial expressions. A total of 81 participants were asked to view two sets of images, (one set of normally configured faces and one scrambled faces) and indicate which images looked the happiest.

The study revealed that when deciding which face looked happier participants tended to choose the left cheek over the right cheek irrespective of whether they were viewing a normal or scrambled face. The discovery of a left cheek bias in normal and scrambled faces, suggests that featural information from the cheeks alone is enough to influence facial emotion perception. However, there was a stronger left cheek bias for normal faces which suggests that configural information is not redundant in emotion perception, but instead enhances the featural information which increases the left cheek bias.

The findings of the study begin to clarify the facial cues behind the left cheek bias in facial emotion perception. The authors state that the study ‘offers further support for the right hemisphere’s dominant role in emotion processing’.