Effects of temporal dynamics on perceived authenticity of smiles

We presented participants with videos of Duchenne smiles that differed in the duration of their onset, offset, or both to determine if this would affect perceived expression authenticity. The duration of onset and offset varied between 0.2 and 1.0 s. Participants were shown one smile at a time and were asked to judge its genuineness on a rating scale. Results indicated the duration of offset had an effect on perceived genuineness when it was manipulated in isolation. Similarly, when both the offset and onset duration were adjusted concomitantly, genuineness ratings were affected. There was no effect of onset duration when it was manipulated in isolation. This is the first demonstration of these effects using photographs of real human faces that are dynamically and morphologically symmetrical, and which have been validated via the Facial Action Coding System.