A Distributional Approach to Controlled Text Generation
Authors: Muhammad Khalifa, Hady Elsahar, Marc Dymetman
Venue: ICLR 2021 Oral
Keywords: Controlled NLG, Pretrained Language Models, Bias in Language Models, Energy-Based Models, Information Geometry, Exponential Families
Abstract: We propose a  Distributional  Approach for addressing  Controlled  Text  Generation from pre-trained Language Models (LM). This approach permits to specify, in a single formal framework, both “pointwise’” and “distributional” constraints over the target LM — to our knowledge, the first model with such generality —while minimizing KL divergence from the initial LM distribution.  The optimal target distribution is then uniquely determined as an explicit EBM (Energy-BasedModel) representation. From that optimal representation, we then train a target controlled Autoregressive LM through an adaptive distributional variant of PolicyGradient.  We conduct a first set of experiments over pointwise constraints showing the advantages of our approach over a set of baselines, in terms of obtaining a controlled LM balancing constraint satisfaction with divergence from the pretrained LM.  We then perform experiments over distributional constraints, a unique feature of our approach, demonstrating its potential as a remedy to the problem of Bias in Language Models.  Through an ablation study, we show the effectiveness of our adaptive technique for obtaining faster convergence.
Code available at https://github.com/naver/gdc