A three-dimensional study of facial mimicry in healthy young adults.

To assess sex-related characteristics in facial movements, and to define a set of reference normal values, 20 healthy young adults (10 men, 10 women) performed six standardized facial movements (maximum smile; free smile; "surprise" with closed mouth; "surprise" with open mouth; right- and left-side eye closures). The three-dimensional coordinates of 21 soft-tissue facial landmarks were recorded by an optoelectronic motion analyzer, their movements computed, and standardized for facial dimensions. Asymmetry indices were calculated. The mouth area had the largest movements. Sex-related differences were found only for the superciliare landmark (men had larger movements than women, p<0.001). Asymmetries in the eyes, mouth and nose were similar in both sexes (p>0.01), with a significant effect of movement (p<0.001): eye and mouth asymmetry was larger during the asymmetric eye closures than during the symmetric movements. The right-side asymmetric movements were somewhat larger than the left-side ones. The total facial movement did not differ between sexes; the "surprise with mouth open" movement had the largest landmark displacements (p<0.001). In conclusion, normal young adult men and women had similar standardized facial movements, except in the forehead. Some individual asymmetry was found in symmetric facial animations; some synkinesis was found even in normal adults.