The action synergies: Building blocks for understanding human behavior

Social signal processing is an emerging field that gains more and more attention. As a key element in the field, visual perception of human motion is important for understanding human behavior in social intelligence. Motivated by the hypothesis of muscle synergies, we proposed action synergies for automatically partitioning human motion into individual action segments in videos. Assuming the size of the human subject is reasonable and the background changes smoothly, the video sequence is represented by six latent variables, which we obtain using Gaussian Process Dynamical Models (GPDM). For each variable, the third order derivative and its local maxima are computed. Then by finding the consistent local maxima in all variables, the video is partitioned into action segments. We demonstrate the usefulness of the algorithm for periodic motion patterns as well as non-periodic ones, using videos of various qualities. Results show that the proposed algorithm partitions videos into meaningful action segments.