Despite recent advances in training recurrent neural networks (RNNs), capturing long-term dependencies in sequences remains a fundamental challenge. Most approaches use backpropagation through time (BPTT), which is difficult to scale to very long sequences. This paper proposes a simple method that improves the ability to capture long term dependencies in RNNs by adding an unsupervised auxiliary loss to the original objective. This auxiliary loss forces RNNs to either reconstruct previous events or predict next events in a sequence, making truncated backpropagation feasible for long sequences and also improving full BPTT. We evaluate our method on a variety of settings, including pixel-by-pixel image classification with sequence lengths up to 16\,000, and a real document classification benchmark. Our results highlight good performance and resource efficiency of this approach over competitive baselines, including other recurrent models and a comparable sized Transformer. Further analyses reveal beneficial effects of the auxiliary loss on optimization and regularization, as well as extreme cases where there is little to no backpropagation.

Abstract: We present a simple method to improve learning long-term dependencies in recurrent neural networks (RNNs) by introducing unsupervised auxiliary losses. These auxiliary losses force RNNs to either remember distant past or predict future, enabling truncated backpropagation through time (BPTT) to work on very long sequences. We experimented on sequences up to 16000 tokens long and report faster training, more resource efficiency and better test performance than full BPTT baselines such as Long Short Term Memory (LSTM) networks or Transformer. TL;DR: Combining auxiliary losses and truncated backpropagation through time in RNNs improves resource efficiency, training speed and generalization in learning long term dependencies.