Continual Backprop: Stochastic Gradient Descent with Persistent Randomness

Shibhansh Dohare, Richard S. Sutton, A. Rupam Mahmood

Keywords: Continual Adaptation, Reinforcement Learning, Continual Learning, Online Learning

Abstract: The Backprop algorithm for learning in neural networks utilizes two mechanisms: first, stochastic gradient descent and second, initialization with small random weights, where the latter is essential to the effectiveness of the former. We show that in continual learning setups, Backprop performs well initially, but over time its performance degrades. Stochastic gradient descent alone is insufficient to learn continually; the initial randomness enables only initial learning but not continual learning. To the best of our knowledge, ours is the first result showing this degradation in Backprop’s ability to learn. To address this issue, we propose an algorithm that continually injects random features alongside gradient descent using a new generate-and-test process. We call this the Continual Backprop algorithm. We show that, unlike Backprop, Continual Backprop is able to continually adapt in both supervised and reinforcement learning problems. We expect that as continual learning becomes more common in future applications, a method like Continual Backprop will be essential where the advantages of random initialization are present throughout learning.

One-sentence Summary: We show that Backprop is unsuitable for continual adaptation and then propose more suitable algorithms