Improving the Gating Mechanism of Recurrent Neural Networks
Authors: Albert Gua, Caglar Gulcehre, Tom le Paine, Razvan Pascanu, Matt Hoffman
Keywords: recurrent neural networks, LSTM, GRUs, gating mechanisms, deep learning, reinforcement learning
TL;DR: Improving the gating mechanisms of recurrent neural networks by addressing the initialization of the biases and the saturation problem of sigmoid.
Abstract: In this work, we revisit the gating mechanisms widely used in various recurrent and feedforward networks such as LSTMs, GRUs, or highway networks. These gates are meant to control information flow, allowing gradients to better propagate back in time for recurrent models. However, to propagate gradients over very long temporal windows, they need to operate close to their saturation regime. We propose two independent and synergistic modifications to the standard gating mechanism that are easy to implement, introduce no additional hyper-parameters, and are aimed at improving learnability of the gates when they are close to saturation. Our proposals are theoretically justified, and we show a generic framework that encompasses other recently proposed gating mechanisms such as chrono-initialization and master gates . We perform systematic analyses and ablation studies on the proposed improvements and evaluate our method on a wide range of applications including synthetic memorization tasks, sequential image classification, language modeling, and reinforcement learning.  Empirically, our proposed gating mechanisms robustly increase the performance of recurrent models such as LSTMs, especially on tasks requiring long temporal dependencies.