Kinematic analysis of a Duchenne smile

• Smiles involved movements mainly in vertical and anteroposterior dimensions.
• Smiles involved movements mainly of the lips, chin, cheeks and lower lateral eyes, but not upper or medial eyes.
• Peak velocities, accelerations and decelerations were greatest in the lower face.

ObjectiveFacial expressions are communicative motor outputs, whose kinematics likely are due to musculoskeletal anatomy, neuromotor activity and the well-being and internal states of the individual. However, little has been published on the kinematics of facial expression. This study quantified lip, eye and cheek movements during the production of a Duchenne smile involving movement of lips and tissues surrounding the eyes.DesignThe three-dimensional positions of 20 markers placed around the eyes, cheeks, lips and chins of 24 young adult female subjects were digitized while they performed smiles after practicing to feedback from an investigator trained in the facial action coding system (FACS). Displacement, velocity and acceleration variables were extracted and analyzed from the markers.ResultsResults demonstrated several consistencies across subjects including: (1) relatively high peak velocities, accelerations and displacements for lip and cheek markers in the vertical and anteroposterior dimensions, (2) relatively large movements of the lower lateral eye region compared with other eye regions.ConclusionThe results indicate that there is significant movement in the anteroposterior dimension that is not observable in frontal views of the face alone.