Deep Learning for Spatio-Temporal Modeling of Dynamic Spontaneous Emotions

Facial expressions involve dynamic morphological changes in a face, conveying information about the expresser's feelings. Each emotion has a specific spatial deformation over the face and temporal profile with distinct time segments. We aim at modeling the human dynamic emotional behavior by taking into consideration the visual content of the face and its evolution. But emotions can both speed-up or slow-down, therefore it is important to incorporate information from the local neighborhood frames (short-term dependencies) and the global setting (long-term dependencies) to summarize the segment context despite of its time variations. A 3D-Convolutional Neural Networks (3D-CNN) is used to learn early local spatiotemporal features. The 3D-CNN is designed to capture subtle spatiotemporal changes that may occur on the face. Then, a Convolutional-Long-Short-Term-Memory (ConvLSTM) network is designed to learn semantic information by taking into account longer spatiotemporal dependencies. The ConvLSTM network helps considering the global visual saliency of the expression. That is locating and learning features in space and time that stand out from their local neighbors in order to signify distinctive facial expression features along the entire sequence. Non-variant representations based on aggregating global spatiotemporal features at increasingly fine resolutions are then done using a weighted Spatial Pyramid Pooling layer.