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  • 1.
    Butepage, Judith
    et al.
    KTH, School of Computer Science and Communication (CSC), Robotics, perception and learning, RPL.
    Black, Michael J.
    Kragic, Danica
    KTH, School of Computer Science and Communication (CSC), Robotics, perception and learning, RPL.
    Kjellström, Hedvig
    KTH, School of Computer Science and Communication (CSC), Robotics, perception and learning, RPL.
    Deep representation learning for human motion prediction and classification2017In: 30th IEEE Conference on Computer Vision and Pattern Recognition (CVPR 2017), IEEE, 2017, p. 1591-1599Conference paper (Refereed)
    Abstract [en]

    Generative models of 3D human motion are often restricted to a small number of activities and can therefore not generalize well to novel movements or applications. In this work we propose a deep learning framework for human motion capture data that learns a generic representation from a large corpus of motion capture data and generalizes well to new, unseen, motions. Using an encoding-decoding network that learns to predict future 3D poses from the most recent past, we extract a feature representation of human motion. Most work on deep learning for sequence prediction focuses on video and speech. Since skeletal data has a different structure, we present and evaluate different network architectures that make different assumptions about time dependencies and limb correlations. To quantify the learned features, we use the output of different layers for action classification and visualize the receptive fields of the network units. Our method outperforms the recent state of the art in skeletal motion prediction even though these use action specific training data. Our results show that deep feedforward networks, trained from a generic mocap database, can successfully be used for feature extraction from human motion data and that this representation can be used as a foundation for classification and prediction.

  • 2.
    Butepage, Judith
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Robotics, Perception and Learning, RPL.
    Kjellström, Hedvig
    KTH, School of Electrical Engineering and Computer Science (EECS), Robotics, Perception and Learning, RPL.
    Kragic, Danica
    KTH, School of Electrical Engineering and Computer Science (EECS), Robotics, Perception and Learning, RPL.
    Anticipating many futures: Online human motion prediction and generation for human-robot interaction2018In: 2018 IEEE INTERNATIONAL CONFERENCE ON ROBOTICS AND AUTOMATION (ICRA), IEEE COMPUTER SOC , 2018, p. 4563-4570Conference paper (Refereed)
    Abstract [en]

    Fluent and safe interactions of humans and robots require both partners to anticipate the others' actions. The bottleneck of most methods is the lack of an accurate model of natural human motion. In this work, we present a conditional variational autoencoder that is trained to predict a window of future human motion given a window of past frames. Using skeletal data obtained from RGB depth images, we show how this unsupervised approach can be used for online motion prediction for up to 1660 ms. Additionally, we demonstrate online target prediction within the first 300-500 ms after motion onset without the use of target specific training data. The advantage of our probabilistic approach is the possibility to draw samples of possible future motion patterns. Finally, we investigate how movements and kinematic cues are represented on the learned low dimensional manifold.

  • 3.
    Bütepage, Judith
    KTH, School of Electrical Engineering and Computer Science (EECS), Robotics, Perception and Learning, RPL.
    Generative models for action generation and action understanding2019Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The question of how to build intelligent machines raises the question of how to rep-resent the world to enable intelligent behavior. In nature, this representation relies onthe interplay between an organism’s sensory input and motor input. Action-perceptionloops allow many complex behaviors to arise naturally. In this work, we take these sen-sorimotor contingencies as an inspiration to build robot systems that can autonomouslyinteract with their environment and with humans. The goal is to pave the way for robotsystems that can learn motor control in an unsupervised fashion and relate their ownsensorimotor experience to observed human actions. By combining action generationand action understanding we hope to facilitate smooth and intuitive interaction betweenrobots and humans in shared work spaces.To model robot sensorimotor contingencies and human behavior we employ gen-erative models. Since generative models represent a joint distribution over relevantvariables, they are flexible enough to cover the range of tasks that we are tacklinghere. Generative models can represent variables that originate from multiple modali-ties, model temporal dynamics, incorporate latent variables and represent uncertaintyover any variable - all of which are features required to model sensorimotor contin-gencies. By using generative models, we can predict the temporal development of thevariables in the future, which is important for intelligent action selection.We present two lines of work. Firstly, we will focus on unsupervised learning ofmotor control with help of sensorimotor contingencies. Based on Gaussian Processforward models we demonstrate how the robot can execute goal-directed actions withthe help of planning techniques or reinforcement learning. Secondly, we present anumber of approaches to model human activity, ranging from pure unsupervised mo-tion prediction to including semantic action and affordance labels. Here we employdeep generative models, namely Variational Autoencoders, to model the 3D skeletalpose of humans over time and, if required, include semantic information. These twolines of work are then combined to implement physical human-robot interaction tasks.Our experiments focus on real-time applications, both when it comes to robot ex-periments and human activity modeling. Since many real-world scenarios do not haveaccess to high-end sensors, we require our models to cope with uncertainty. Additionalrequirements are data-efficient learning, because of the wear and tear of the robot andhuman involvement, online employability and operation under safety and complianceconstraints. We demonstrate how generative models of sensorimotor contingencies canhandle these requirements in our experiments satisfyingly.

  • 4.
    Bütepage, Judith
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Robotics, Perception and Learning, RPL.
    Kjellström, Hedvig
    KTH, School of Electrical Engineering and Computer Science (EECS), Robotics, Perception and Learning, RPL.
    Kragic, Danica
    KTH, School of Electrical Engineering and Computer Science (EECS), Robotics, Perception and Learning, RPL.
    A Probabilistic Semi-Supervised Approach to Multi-Task Human Activity ModelingManuscript (preprint) (Other academic)
    Abstract [en]

    Human behavior is a continuous stochastic spatio-temporal process which is governed by semantic actions and affordances as well as latent factors. Therefore, video-based human activity modeling is concerned with a number of tasks such as inferring current and future semantic labels, predicting future continuous observations as well as imagining possible future label and feature sequences. In this paper we present a semi-supervised probabilistic deep latent variable model that can represent both discrete labels and continuous observations as well as latent dynamics over time. This allows the model to solve several tasks at once without explicit fine-tuning. We focus here on the tasks of action classification, detection, prediction and anticipation as well as motion prediction and synthesis based on 3D human activity data recorded with Kinect. We further extend the model to capture hierarchical label structure and to model the dependencies between multiple entities, such as a human and objects. Our experiments demonstrate that our principled approach to human activity modeling can be used to detect current and anticipate future semantic labels and to predict and synthesize future label and feature sequences. When comparing our model to state-of-the-art approaches, which are specifically designed for e.g. action classification, we find that our probabilistic formulation outperforms or is comparable to these task specific models.

  • 5.
    Zhang, Cheng
    et al.
    Microsoft Res, Cambridge CB1 2FB, England..
    Butepage, Judith
    KTH, School of Electrical Engineering and Computer Science (EECS), Robotics, Perception and Learning, RPL.
    Kjellström, Hedvig
    KTH, School of Electrical Engineering and Computer Science (EECS), Robotics, Perception and Learning, RPL.
    Mandt, Stephan
    Advances in Variational Inference2019In: IEEE Transaction on Pattern Analysis and Machine Intelligence, ISSN 0162-8828, E-ISSN 1939-3539, Vol. 41, no 8, p. 2008-2026Article in journal (Refereed)
    Abstract [en]

    Many modern unsupervised or semi-supervised machine learning algorithms rely on Bayesian probabilistic models. These models are usually intractable and thus require approximate inference. Variational inference (VI) lets us approximate a high-dimensional Bayesian posterior with a simpler variational distribution by solving an optimization problem. This approach has been successfully applied to various models and large-scale applications. In this review, we give an overview of recent trends in variational inference. We first introduce standard mean field variational inference, then review recent advances focusing on the following aspects: (a) scalable VI, which includes stochastic approximations, (b) generic VI, which extends the applicability of VI to a large class of otherwise intractable models, such as non-conjugate models, mean field approximation or with atypical divergences, and (d) amortized VI, which implements the inference over local latent variables with inference networks. Finally, we provide a summary of promising future research directions.

1 - 5 of 5
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