GATO: Gates Are Not the Only Option
Authors: Mark Goldstein*, Xintian Han*, Rajesh Ranganath
Keywords: Sequence Models, Vanishing Gradients, Recurrent neural networks, Long-term dependence
TL;DR: Recurrent neural networks can avoid vanishing gradients by not using all of their hidden state in recurrences, together with a residual structure.
Abstract: Recurrent Neural Networks (RNNs) facilitate prediction and generation of structured temporal data such as text and sound. However, training RNNs is hard. Vanishing gradients cause difficulties for learning long-range dependencies. Hidden states can explode for long sequences and send unbounded gradients to model parameters, even when hidden-to-hidden Jacobians are bounded. Models like the LSTM and GRU use gates to bound their hidden state, but most choices of gating functions lead to saturating gradients that contribute to, instead of alleviate, vanishing gradients. Moreover, performance of these models is not robust across random initializations. In this work, we specify desiderata for sequence models. We develop one model that satisfies them and that is capable of learning long-term dependencies, called GATO. GATO is constructed so that part of its hidden state does not have vanishing gradients, regardless of sequence length. We study GATO on copying and arithmetic tasks with long dependencies and on modeling intensive care unit and language data. Training GATO is more stable across random seeds and learning rates than GRUs and LSTMs. GATO solves these tasks using an order of magnitude fewer parameters.