Kinematic Characterization of Spontaneous and Posed Facial Expressions of Happiness and Surprise

The relationship between emotions and facial expressions has been largely studied. However, most studies have focused on static and posed facial displays. Research on dynamic spontaneous facial expressions is still needed to understand how humans move their face to genuinely express emotion. Therefore, we conducted a study in which spontaneous and posed facial expressions of six basic emotions (happiness, sadness, anger, fear, disgust, and surprise), were recorded. Spontaneous facial expressions were recorded while participants watched emotion-eliciting videos, specifically selected to elicit the list of target emotions. Posed facial expressions, instead, were recorded while participants were instructed to reproduce a specific facial display while watching static pictures of that display. This thesis consists of an overview about emotion, facial expressions and measuring techniques, and a complete analysis and comparison of facial expressions of happiness and surprise. In particular, we considered the role played by the facial horizontal axis (i.e., the axis dividing the lower and upper parts of the face) in emotion expression. I found different dynamic properties between spontaneous and posed expressions for happiness and surprise. I also found that the upper and lower parts of the face are involved to different degrees in expressions of happiness and surprise. My study provides important evidence to overcome the bias introduced by research that for years has not considered spontaneous expressions or dynamic aspects, and further knowledge that is key for real life applications in clinical, security, and forensic fields.