Multi-person activity recognition is a challenging task due to its elusive interactions in activities. We take into account these interactions at two levels. At the individual level, each person behaves depending on both its spatio-temporal features and interactions propagated from others in the scene. At the scene level, the multi-person activity is characterized by interactions between individuals' actions and the high-level activity. It is worth noting that interactions contribute unequally at both levels. To jointly explore these colorful interactions, we propose a two-level attention-based interaction model relying on two time-varying attention mechanisms. The individual-level attention mechanism conditioned on pose features, exploits various degrees of interactions among individuals in a scene while updating their states at each time step. The scene-level attention mechanism proposes an attention-based pooling strategy to explore various levels of interactions between individuals' actions and the high-level activity. We ground our model by a modified two-stage Gated Recurrent Units (GRUs) network to handle the long-range temporal variability and consistency. Our end-to-end trainable model takes as inputs a set of person detections in videos or image sequences and predicts labels of multi-person activities. Experimental results demonstrate comparable performance of our model and show the effectiveness of our attention mechanisms. (C) 2018 Elsevier B. V. All rights reserved.
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