Encoders and Ensembles for Task-Free Continual Learning

We present an architecture that is effective for continual learning in an especially demanding setting, where task boundaries do not exist or are unknown. Our architecture comprises an encoder, pre-trained on a separate dataset, and an ensemble of simple one-layer classifiers. Two main innovations are required to make this combination work. First, the provision of suitably generic pre-trained encoders has been made possible thanks to recent progress in self-supervised training methods. Second, pairing each classifier in the ensemble with a key, where the key-space is identical to the latent space of the encoder, allows them to be used collectively, yet selectively, via k-nearest neighbour lookup. We show that models trained with the encoders-and-ensembles architecture are state-of-the-art for the task-free setting on standard image classification continual learning benchmarks, and improve on prior state-of-the-art by a large margin in the most challenging cases. We also show that the architecture learns well in a fully incremental setting, where one class is learned at a time, and we demonstrate its effectiveness in this setting with up to 100 classes. Finally, we show that the architecture works in a task-free continual learning context where the data distribution changes gradually, and existing approaches requiring knowledge of task boundaries cannot be applied.