Emotional lateralisation in the second year of life: Evidence from oral asymmetries

Abstract

Oral asymmetries for positive and negative emotional expressions were studied in 41 infants, ranging in age from 12 to 24 months. Single-frame analysis of videotapes of each infant's mouth showed that the left side of the mouth opened wider than the right side during negative emotional expressions but a mirror-image effect was not found for the expression of positive emotion. In addition, this directional bias strengthened with age. These results are interpreted as reflecting lateralisation of negative emotional production to the right hemisphere in infants as young as 12 months of age, a developmental enhancement of right hemisphere control of negative emotional expression that is evident by 24 months of age, and an absence of lateralisation for positive emotional expression in infants between 12 and 24 months of age.