On Retrieval Augmentation and the Limitations of Language Model Training
Ting-Rui Chiang, Xinyan Yu, Joshua Robinson, Ollie Liu, Isabelle Lee, Dani Yogatama
Abstract
Augmenting a language model (LM) with k-nearest neighbors (kNN) retrieval on its training data alone can decrease its perplexity, though the underlying reasons for this remain elusive. In this work, we rule out one previously posited possibility — the “softmax bottleneck.” We then create a new dataset to evaluate LM generalization ability in the setting where training data contains additional information that is not causally relevant. This task is challenging even for GPT-3.5 Turbo. We show that, for both GPT-2 and Mistral 7B, kNN retrieval augmentation consistently improves per formance in this setting. Finally, to make kNN retrieval more accessible, we propose using amulti-layer perceptron model that maps datastore keys to values as a drop-in replacement for traditional retrieval. This reduces storage costsby over 25x.
BibTeX
@inproceedings{chiang-etal-2024-retrieval,
title = "On Retrieval Augmentation and the Limitations of Language Model Training",
author = "Chiang, Ting-Rui and
Yu, Xinyan and
Robinson, Joshua and
Liu, Ollie and
Lee, Isabelle and
Yogatama, Dani",
editor = "Duh, Kevin and
Gomez, Helena and
Bethard, Steven",
booktitle = "Proceedings of the 2024 Conference of the North American Chapter of the Association for Computational Linguistics: Human Language Technologies (Volume 2: Short Papers)",
month = jun,
year = "2024",
address = "Mexico City, Mexico",
publisher = "Association for Computational Linguistics",
url = "https://aclanthology.org/2024.naacl-short.21/",
doi = "10.18653/v1/2024.naacl-short.21",
pages = "229--238"
}