Figure 3.

Kinematic parameters. (a) Example of one trial. The black line represents the excursion of the markers placed on the participant's mouth. The movement began after the participants observed the actress's smile and maintained the posture for about three seconds. The baseline is shown in gray. In this phase, the subject did not perform any movement. (b) Three reflective passive markers were placed on the participant's face (left mouth marker, LMM; right mouth marker, RMM; and reference marker, RM). Bilateral smile amplitude was calculated as the maximum Euclidian distance (MMA) in millimeters between the two lip corner markers (LMM and RMM). This measure was expressed as a percentage of the MMA at baseline (%MMA). Similarly, left/right side parameters were calculated as the Euclidian distances in millimeters between LMM or RMM lip corner marker and the nose marker (RM). Left/right side parameters were expressed as the percentage of side baseline (left or right, respectively, before movement onset).