Eyes do not lie: Spontaneous versus posed smiles

Automatic detection of spontaneous versus posed facial expressions received a lot of attention in recent years. However, almost all published work in this area use complex facial features or multiple modalities, such as head pose and body movements with facial features. Besides, the results of these studies are not given on public databases. In this paper, we focus on eyelid movements to classify spontaneous versus posed smiles and propose distance-based and angular features for eyelid movements. We assess the reliability of these features with continuous HMM, k-NN and naive Bayes classifiers on two different public datasets. Experimentation shows that our system provides classification rates up to 91 per cent for posed smiles and up to 80 per cent for spontaneous smiles by using only eyelid movements. We additionally compare the discrimination power of movement features from different facial regions for the same task.