Dynamics of facial expression: normative characteristics and individual differences

Although the importance of facial expression in human computer interaction and in normal human interaction is widely acknowledged, there is very little data on the normative characteristics and stable individual differences for even the most common facial expressions. Dynamic characteristics of 195 spontaneous smiles from 95 individuals were measured using the facial action coding system, automated facial analysis and facial electromyography. Normative patterns observed included the characteristic timing of other facial actions with respect to action unit 12 (“smile”) and a mean duration of 15.7 frames for smile onset. Stable inter-individual differences included patterns of nonverbal actions associated with individuals’ smiles, and the amount of activity in the zygomaticus major muscle in two sessions recorded a year apart. These data are important in quantifying and fully describing individual differences in naturalistic human facial expression, as well as adding to our knowledge of spontaneous human smiles.