MixCE: Training Autoregressive Language Models by Mixing Forward and Reverse Cross-Entropies

Shiyue Zhang, Shijie Wu, Ozan Irsoy, Steven Lu, Mohit Bansal, Mark Dredze, David Rosenberg

Main: Large Language Models Main-poster Paper

Poster Session 2: Large Language Models (Poster)
Conference Room: Frontenac Ballroom and Queen's Quay
Conference Time: July 10, 14:00-15:30 (EDT) (America/Toronto)
Global Time: July 10, Poster Session 2 (18:00-19:30 UTC)
Keywords: fine-tuning
TLDR: Autoregressive language models are trained by minimizing the cross-entropy of the model distribution Q relative to the data distribution P – that is, minimizing the forward cross-entropy, which is equivalent to maximum likelihood estimation (MLE). We have observed that models trained in this way may...
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Abstract: Autoregressive language models are trained by minimizing the cross-entropy of the model distribution Q relative to the data distribution P – that is, minimizing the forward cross-entropy, which is equivalent to maximum likelihood estimation (MLE). We have observed that models trained in this way may "over-generalize”, in the sense that they produce non-human-like text. Moreover, we believe that reverse cross-entropy, i.e., the cross-entropy of P relative to Q, is a better reflection of how a human would evaluate text generated by a model. Hence, we propose learning with MixCE, an objective that mixes the forward and reverse cross-entropies. We evaluate models trained with this objective on synthetic data settings (where P is known) and real data, and show that the resulting models yield better generated text without complex decoding strategies.