An Interactive Framework for Learning Continuous Actions Policies Based on Corrective Feedback


The main goal of this article is to present COACH (COrrective Advice Communicated by Humans), a new learning framework that allows non-expert humans to advise an agent while it interacts with the environment in continuous action problems. The human feedback is given in the action domain as binary corrective signals (increase/decrease the current action magnitude), and COACH is able to adjust the amount of correction that a given action receives adaptively, taking state-dependent past feedback into consideration. COACH also manages the credit assignment problem that normally arises when actions in continuous time receive delayed corrections. The proposed framework is characterized and validated extensively using four well-known learning problems. The experimental analysis includes comparisons with other interactive learning frameworks, with classical reinforcement learning approaches, and with human teleoperators trying to solve the same learning problems by themselves. In all the reported experiments COACH outperforms the other methods in terms of learning speed and final performance. It is of interest to add that COACH has been applied successfully for addressing a complex real-world learning problem: the dribbling of the ball by humanoid soccer players.

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This work was partially funded by FONDECYT project 1161500 and CONICYT-PCHA/Doctorado Nacional/2015-21151488.

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Correspondence to Carlos Celemin.

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Given that human feedback is a key component of the proposed learning framework, a new Hand-Gesture Recognition (HGR) interface that allows providing feedback to the agent is proposed. The interface allows detecting 5 gestures: positive correction, negative correction, a neutral gesture used when users do not need to provide feedback, a reward, and a punishment (see gestures in Fig. 15).

Fig. 15

Examples of recognized hand gestures

In order for the proposed system to be robust to variations in illumination, colors, and non-uniform backgrounds, it uses: (i) Gaussian Mixture Models (GMM) and based Background Subtraction (BS) to detect regions of interest (ROI), i.e. hand candidates, (ii) Kalman filtering for tracking the hand candidates, (iii) Local Binary Patterns (LBP) as features for characterizing the ROIs, and (iv) SVM classifiers for the final detection of the hand-gestures. The block diagram is shown in Fig. 16. The main functionalities are described in the following paragraphs:

  • Detection of Regions of Interest (ROI): Movement blobs are first detected using background subtraction. Then, adjacent blobs are merged and filtered using morphological filters, and the largest blob is selected as a hand candidate and fed to the tracking system.

    In parallel, a second process applies BS to color edges: First, a binary edge image is computed, and then color information is incorporated into the edges. Afterwards, BS and area filtering is applied in the edge’s domain. Finally, the output of the area-filtering module is intersected with the color edges in the block “&”. In order to manage occlusions properly (see Fig. 16b) the block “&” deletes the blobs associated with the occluded edges, which are labeled by BS as regions with movement (Fig. 15 left); since those edges are not present in the original image. The output is a blob with the detected moving, color edges (Fig. 17 right).

  • Tracking: The parameters of the bounding box of the largest blob taken as a hand candidate by the prior module are used as observations by a Kalman filter, which estimates the final hand candidates, based on the fusion of the current ROI information with the prior ones. Afterwards, the image computed in the block “&” of the previous module is intersected with the Kalman-filtered bounding box. Examples of the resulting images are shown in Fig. 15.

  • Features Extraction and Classification: The image window given by the Tracking module is analyzed in order to classify the captured gesture. Histograms of LBP features are computed inside the image window. Since this window is a binary image, LBP are used as discretized measurements of the gradient. Then, the histograms of the LBP features are similar to Histograms of Gradient (HOG). This feature vector feeds five SVM classifiers, one trained for each gesture, where the gestures are detected.

Fig. 16

Hand gesture recognition system. a General scheme, b Detailed scheme

Fig. 17

Hands occluding edges in the edges domain (left), results of the intersection “&” module (right)

The dataset used for training the SVM was built using images generated by the tracking module. Altogether, 1654 images of the five hand-gestures were recorded, 60% of them used for training, and 40% for validation. The classification error is 9.05%, which is considered appropriate to be used as an interface for the learning problems described in Section 4.

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Celemin, C., Ruiz-del-Solar, J. An Interactive Framework for Learning Continuous Actions Policies Based on Corrective Feedback. J Intell Robot Syst 95, 77–97 (2019).

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  • Learning from demonstration
  • Interactive machine learning
  • Human feedback
  • Human teachers
  • Decision making systems