This episode explores a 2017 paper arguing that sigmoid-weighted activation functions, specifically SiLU and dSiLU, can materially improve deep reinforcement learning when paired with replay-free Sarsa(lambda), eligibility traces, and softmax exploration. It explains why activation choice matters more in bootstrapped value learning than in ordinary supervised settings, and uses that as a lens to unpack older RL concepts like function approximation, TD(lambda), and on-policy learning for listeners coming from modern deep learning. The discussion walks through the paper’s results on SZ-Tetris, 10x10 Tetris, and Atari-style settings, highlighting that dSiLU and mixed SiLU/dSiLU networks outperformed ReLU-based alternatives in several configurations. Listeners would find it interesting because it challenges the idea that replay buffers and DQN-style machinery are the only serious path for high-dimensional RL, and shows how a seemingly small architectural choice can reshape learning dynamics. Sources: 1. Sigmoid-Weighted Linear Units for Neural Network Function Approximation in Reinforcement Learning — Stefan Elfwing, Eiji Uchibe, Kenji Doya, 2017 http://arxiv.org/abs/1702.03118 2. Bridging Nonlinearities and Stochastic Regularizers with Gaussian Error Linear Units — Dan Hendrycks, Kevin Gimpel, 2016 https://scholar.google.com/scholar?q=Bridging+Nonlinearities+and+Stochastic+Regularizers+with+Gaussian+Error+Linear+Units 3. Sigmoid-Weighted Linear Units for Neural Network Function Approximation in Reinforcement Learning — Stefan Elfwing, Eiji Uchibe, Kenji Doya, 2017 https://scholar.google.com/scholar?q=Sigmoid-Weighted+Linear+Units+for+Neural+Network+Function+Approximation+in+Reinforcement+Learning 4. Searching for Activation Functions — Prajit Ramachandran, Barret Zoph, Quoc V. Le, 2017 https://scholar.google.com/scholar?q=Searching+for+Activation+Functions 5. GLU Variants Improve Transformer — Noam Shazeer, 2020 https://scholar.google.com/scholar?q=GLU+Variants+Improve+Transformer 6. Learning to Predict by the Methods of Temporal Differences — Richard S. Sutton, 1988 https://scholar.google.com/scholar?q=Learning+to+Predict+by+the+Methods+of+Temporal+Differences 7. True Online Temporal-Difference Learning — Harm van Seijen, A. Rupam Mahmood, Patrick M. Pilarski, Marlos C. Machado, Richard S. Sutton, 2015 https://scholar.google.com/scholar?q=True+Online+Temporal-Difference+Learning 8. High-Dimensional Continuous Control Using Generalized Advantage Estimation — John Schulman, Philipp Moritz, Sergey Levine, Michael Jordan, Pieter Abbeel, 2015 https://scholar.google.com/scholar?q=High-Dimensional+Continuous+Control+Using+Generalized+Advantage+Estimation 9. Multi-step Reinforcement Learning: A Unifying Algorithm — Kristopher De Asis, J. Fernando Hernandez-Garcia, G. Zacharias Holland, Richard S. Sutton, 2017 https://scholar.google.com/scholar?q=Multi-step+Reinforcement+Learning:+A+Unifying+Algorithm 10. Playing Atari with Deep Reinforcement Learning — Volodymyr Mnih, Koray Kavukcuoglu, David Silver, Alex Graves, Ioannis Antonoglou, Daan Wierstra, Martin Riedmiller, 2013 https://scholar.google.com/scholar?q=Playing+Atari+with+Deep+Reinforcement+Learning 11. Asynchronous Methods for Deep Reinforcement Learning — Volodymyr Mnih, Adrià Puigdomènech Badia, Mehdi Mirza, Alex Graves, Timothy P. Lillicrap, Tim Harley, David Silver, Koray Kavukcuoglu, 2016 https://scholar.google.com/scholar?q=Asynchronous+Methods+for+Deep+Reinforcement+Learning 12. Proximal Policy Optimization Algorithms — John Schulman, Filip Wolski, Prafulla Dhariwal, Alec Radford, Oleg Klimov, 2017 https://scholar.google.com/scholar?q=Proximal+Policy+Optimization+Algorithms 13. Training Language Models to Follow Instructions with Human Feedback — Long Ouyang, Jeff Wu, Xu Jiang, Diogo Almeida, Carroll L. Wainwright, Pamela Mishkin, Chong Zhang, Sandhini Agarwal, Katarina Slama, Alex Ray, John Schulman, Jacob Hilton, Fraser Kelton, Luke Miller, Maddie Simens, Amanda Askell, Peter Welinder, Paul Christiano, Jan Leike, Ryan Lowe, 2022 https://scholar.google.com/scholar?q=Training+Language+Models+to+Follow+Instructions+with+Human+Feedback 14. Human-level control through deep reinforcement learning — Volodymyr Mnih et al., 2015 https://scholar.google.com/scholar?q=Human-level+control+through+deep+reinforcement+learning 15. Deep reinforcement learning with double q-learning — Hado van Hasselt, Arthur Guez, David Silver, 2015 https://scholar.google.com/scholar?q=Deep+reinforcement+learning+with+double+q-learning 16. Prioritized Experience Replay — Tom Schaul, John Quan, Ioannis Antonoglou, David Silver, 2016 https://scholar.google.com/scholar?q=Prioritized+Experience+Replay 17. High-dimensional function approximation for knowledge-free reinforcement learning: a case study in SZ-Tetris — Wojciech Jaskowski, Maciej Szubert, Pawel Liskowski, Krzysztof Krawiec, 2015 https://scholar.google.com/scholar?q=High-dimensional+function+approximation+for+knowledge-free+reinforcement+learning:+a+case+study+in+SZ-Tetris 18. Approximate dynamic programming finally performs well in the game of tetris — Victor Gabillon, Mohammad Ghavamzadeh, Bruno Scherrer, 2013 https://scholar.google.com/scholar?q=Approximate+dynamic+programming+finally+performs+well+in+the+game+of+tetris 19. Replay across Experiments: A Natural Extension of Off-Policy RL — Dhruva Tirumala et al., 2023 https://arxiv.org/abs/2311.15951 20. Adaptive Q-Network: On-the-fly Target Selection for Deep Reinforcement Learning — Theo Vincent et al., 2024 https://arxiv.org/abs/2405.16195 21. A Survey of Temporal Credit Assignment in Deep Reinforcement Learning — Eduardo Pignatelli et al., 2023 https://arxiv.org/abs/2312.01072 22. AI Post Transformers: ASI-Evolve for Data, Architectures, and RL — Hal Turing & Dr. Ada Shannon, 2026 https://podcast.do-not-panic.com/episodes/2026-04-05-asi-evolve-for-data-architectures-and-rl-197b2b.mp3 23. AI Post Transformers: LeWorldModel: Stable Joint-Embedding World Models from Pixels — Hal Turing & Dr. Ada Shannon, 2026 https://podcast.do-not-panic.com/episodes/2026-03-25-leworldmodel-stable-joint-embedding-worl-650f9f.mp3