Human action is naturally compositional: humans can easily recognize and perform actions with objects that are different from those used in training demonstrations. In this paper, we study the compositionality of action by looking into the dynamics of subject-object interactions. We propose a novel model which can explicitly reason about the geometric relations between constituent objects and an agent performing an action. To train our model, we collect dense object box annotations on the Something-Something dataset. We propose a novel compositional action recognition task where the training combinations of verbs and nouns do not overlap with the test set. The novel aspects of our model are applicable to activities with prominent object interaction dynamics and to objects which can be tracked using state-of-the-art approaches; for activities without clearly defined spatial object-agent interactions, we rely on baseline scene-level spatio-temporal representations. We show the effectiveness of our approach not only on the proposed compositional action recognition task, but also in a few-shot compositional setting which requires the model to generalize across both object appearance and action category.

本文提出一种新颖的机器学习模型，通过对主体-对象交互的动态学习来探究行为的组成性。该模型能够精确推理组成对象的几何关系和动作代理之间的关系，具有较好的应用前景。在使用Something-Something数据集进行训练时，我们提出了一种新的组合性行为识别任务，成功验证了该模型的有效性。

空间时态交互网络的组合动作识别