Deep Recurrent Q-Learning for Partially Observable MDPs
Matthew HausknechtPeter Stone
Introduces Deep Recurrent Q-Networks by integrating an LSTM into standard Deep Q-Networks, demonstrating that recurrent memory allows reinforcement learning agents to handle partially observable environments and better adapt to degraded visual inputs than traditional frame-stacking methods.
Real-world autonomous systems and decision-making controllers frequently operate in noisy, uncertain environments where sensors provide incomplete state information. Standard deep reinforcement learning methods, such as the standard Deep Q-Network, assume full observability by feeding a short, fixed history of recent frames directly into the network. This approach fails to handle conditions where essential data is obscured or requires longer-term memory. The article addresses this operational vulnerability by evaluating whether integrating recurrent memory allows reinforcement learning controllers to maintain performance under partial observability.
The article set out to demonstrate whether adding a recurrent Long Short-Term Memory layer to a deep Q-learning architecture enables an agent to integrate visual observations across time and better handle environments with incomplete state information. To evaluate this approach, the authors modified the standard Deep Q-Network into a Deep Recurrent Q-Network by replacing its first fully connected layer with a recurrent memory layer. They evaluated this framework across nine standard Atari video games and artificially induced partial observability using a flickering setting where screen frames were obscured with a 50 percent probability. Training utilized randomized mini-batches from replay memory with ten unrolled timesteps across ten million iterations per task.
The findings show that the recurrent network matches standard baseline performance across fully observable games despite processing only a single frame per timestep rather than a four-frame stack. In specific environments, such as Frostbite and Double Dunk, the recurrent network outperformed the standard baseline, achieving a score of 2,875 compared to 519 in Frostbite. Furthermore, when trained under full visibility and evaluated across environments with increasing degrees of obscured frames, the recurrent controller degraded significantly less than the standard baseline, retaining a higher percentage of its original score across all levels of missing information. However, across standard benchmarks as a whole, the recurrent network showed no systematic advantage over simple frame stacking, and in some games, like Beam Rider, it scored less than half of the baseline.
These results demonstrate that recurrent memory functions as a robust alternative to stacking fixed frame histories, providing greater resilience when observation quality degrades at deployment time. For decision-makers, choosing a recurrent architecture represents an effective strategy to mitigate operational risks in dynamic environments where sensor streams may drop frames or suffer intermittent occlusions. While recurrency does not provide universal performance gains, its ability to generalize from clean training data to degraded operational conditions makes it a safer architecture for real-world deployment.
Organizations deploying visual reinforcement learning systems in noisy or variable sensor conditions should consider recurrent architectures when operational observability cannot be guaranteed. However, engineering teams should evaluate specific task dynamics before deployment, as stacking frames remains simpler and computationally lighter for static, fully observable tasks. Future work should focus on identifying domain characteristics that favor recurrent architectures and exploring architectures with higher memory capacities without incurring excessive computational training overhead.
Readers should note that the evaluation is limited to a benchmark suite of nine arcade games and synthetic flickering conditions rather than physical real-world sensory inputs. Additionally, training recurrent architectures requires substantially higher compute time, with deeper sequence unrolling increasing computational burden significantly. Confidence remains high that recurrent networks improve robustness under observational degradation, but caution is warranted before expecting universal score improvements across all task domains.
- Paper: Human-level control through deep reinforcement learning, Volodymyr Mnih et al. (2015). This seminal paper introduces the Deep Q-Network (DQN) architecture and experience replay mechanism that the source directly augments with recurrent LSTM layers.
- Paper: Playing Atari with Deep Reinforcement Learning, Volodymyr Mnih et al. (2013). This work establishes learning policies directly from raw Atari pixel frames via stacked observations, defining the baseline approach that the source aims to improve upon under partial observability.
- Paper: Long Short-Term Memory, Sepp Hochreiter et al. (1997). This foundation paper introduces Long Short-Term Memory (LSTM) recurrent networks, which the source integrates into DQN to maintain memory over time.
- Paper: Technical Note: Q-Learning, CHRISTOPHER J.C.H. WATKINS et al. (2004). This paper establishes the mathematical formulation and convergence proof of model-free Q-learning that forms the theoretical backbone of the source's reinforcement learning method.
- Paper: Long-term Recurrent Convolutional Networks for Visual Recognition and Description, Jeff Donahue et al. (2015). This work details the architectural integration of convolutional visual encoders with recurrent LSTM layers to process temporal visual sequences.
- Paper: On the difficulty of training recurrent neural networks, Razvan Pascanu et al. (2012). This analysis of gradient difficulties and training dynamics in recurrent networks provides vital context for understanding how recurrent layers behave during backpropagation through time.
- Paper: Learning to Predict by the Methods of Temporal Differences, Richard S. Sutton (1988). This foundational text introduces temporal-difference learning methods, which underpin the value updates used in deep Q-learning.
- Paper: Reinforcement Learning: A Survey, Leslie Pack Kaelbling et al. (1996). This classic survey provides essential conceptual foundations on Markov decision processes and reinforcement learning principles.
- Paper: Recurrent Experience Replay in Distributed Reinforcement Learning, Steven Kapturowski et al. (2019). This paper directly extends recurrent deep Q-learning to distributed systems with prioritized experience replay by addressing recurrent state staleness and initialization.
- Paper: Asynchronous Methods for Deep Reinforcement Learning, Volodymyr Mnih et al. (2016). This work builds on deep reinforcement learning across Atari benchmarks by introducing asynchronous parallel actor architectures that incorporate recurrent LSTM policies.
- Paper: Learning to Navigate in Complex Environments, Piotr Mirowski et al. (2017). This paper applies recurrent deep reinforcement learning architectures to solve partially observable 3D navigation tasks using auxiliary predictive objectives.
- Paper: Reinforcement Learning with Unsupervised Auxiliary Tasks, Max Jaderberg et al. (2017). This work enhances recurrent deep RL architectures with unsupervised auxiliary sensorimotor tasks to accelerate learning under sparse reward signals.
- Paper: Rainbow: Combining Improvements in Deep Reinforcement Learning, Matteo Hessel et al. (2017). This benchmark work synthesizes subsequent key innovations in value-based deep reinforcement learning beyond standard DQN.
- Paper: Deep Reinforcement Learning with Double Q-learning, Hado van Hasselt et al. (2016). This article addresses severe value overestimation in deep Q-learning by introducing Double DQN, improving the stability of Q-value estimation.
- Paper: Prioritized Experience Replay, Tom Schaul et al. (2016). This research introduces prioritized experience replay, replacing the uniform replay sampling strategy utilized in standard and recurrent DQNs.
- Paper: Dueling Network Architectures for Deep Reinforcement Learning, Ziyu Wang et al. (2016). This paper develops the dueling network architecture to factor state value and action advantages, offering a complementary structural improvement over standard deep Q-networks.
- Paper: A Brief Survey of Deep Reinforcement Learning, Kai Arulkumaran et al. (2017). This survey provides a comprehensive synthesis of the evolution of deep reinforcement learning paradigms, placing recurrent Q-learning within the broader landscape.
