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About this paper

Shufan Wang, Yixiao Song, Andrew Drozdov, Aparna Garimella, Varun Manjunatha, Mohit Iyyer

Interpolation-based retrieval-augmented language models like kNN-LM and TRIME achieve substantial perplexity reductions but do not yield corresponding improvements in open-ended text generation quality. This arises from the retriever's limited token-level benefits and its declining reliability due to exposure bias during long sequence generation.

Key insights

  • Lower perplexity in interpolation-based RALMs (kNN-LM, TRIME) does not guarantee better open-ended text generation quality.
  • kNN-LM only improves the perplexity of a minority (42%) of individual gold tokens, potentially worsening predictions for the majority.
  • The retriever's reliability deteriorates due to exposure bias as generated sequence length increases, leading to less confident and more divergent predictions.

Summary by alphaXiv.

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