Hierarchical SOM-based detection of novel behavior for 3D human tracking

We present a hierarchical SOM-based architecture for the detection of novel human behavior in indoor environments. The system can unsupervisedly learn normal activity and then report novel behavioral patterns as abnormal. The learning stage is based on the clustering of motion with self-organizing maps. With this approach, no domain-specific knowledge on normal actions is required. During the tracking stage, we extract human motion properties expressed in terms of multidimensional flow vectors. From this representation, three classes of motion descriptors are encoded: trajectories, body features and directions. During the training phase, SOM networks are responsible for learning a specific class of descriptors. For a more accurate clustering of motion, we detect and remove outliers from the training data. At detection time, we propose a hybrid neural-statistical method for 3D posture recognition in real time. New observations are tested for novelty and reported if they deviate from the learned behavior. Experiments were performed in two different tracking scenarios with fixed and mobile depth sensor. In order to exhibit the validity of the proposed methodology, several experimental setups and the evaluation of obtained results are presented.