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Front. Robot. AI | doi: 10.3389/frobt.2019.00072

Compositional Learning of Human Activities with a Self-organizing Neural Architecture

  • 1Department of Informatics, Knowledge Technology, Universität Hamburg, Germany

An important step for assistive systems and robot companions operating in human environments is to learn the compositionality of human activities, i.e, recognize both activities and their comprising actions.
Most existing approaches address action and activity recognition as separate tasks, i.e., actions need to be inferred before the activity labels, and are thus highly sensitive to the correct temporal segmentation of the activity sequences.
In this paper, we present a novel learning approach that jointly learns human activities on two levels of semantic and temporal complexity:~1)~transitive actions such as reaching and opening, e.g. a cereal box, and 2) high-level activities such as having breakfast.
Our model consists of a hierarchy of GWR networks which process and learn inherent spatiotemporal dependencies of multiple visual cues extracted from the human body skeletal representation and the interaction with objects.
The neural architecture learns and semantically segments input RGB-D sequences of high-level activities into their composing actions, without supervision.
We investigate the performance of our architecture with a set of experiments on a publicly available benchmark dataset.
The experimental results show that our approach outperforms the state of the art with respect to the classification of the high-level activities.
Additionally, we introduce a novel top-down modulation mechanism to the architecture which uses the actions and activity labels as constraints during the learning phase.
In our experiments, we show how this mechanism can be used to control the network's neural growth without decreasing the overall performance.

Keywords: Human activity recognition, self-organizing networks, hierarchical learning, compositionality of human activities, RGB-D perception

Received: 31 May 2019; Accepted: 30 Jul 2019.

Copyright: © 2019 Mici, Parisi and Wermter. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

* Correspondence: Dr. Luiza Mici, Universität Hamburg, Department of Informatics, Knowledge Technology, Hamburg, Germany,