A Simple yet Effective Self-Debiasing Framework for Transformer Models
Xiaoyue Wang Lijie Wang Xin Liu Suhang Wu Jinsong Su Hua Wu
Current Transformer-based natural language understanding (NLU) models heavily
rely on dataset biases, while failing to handle real-world out-of-distribution
(OOD) instances. Many methods have been proposed to deal with this issue, but
they ignore the fact that the features learned in different layers of
Transformer-based NLU models are different. In this paper, we first conduct
preliminary studies to obtain two conclusions: 1) both low- and high-layer
sentence representations encode common biased features during training; 2) the
low-layer sentence representations encode fewer unbiased features than the
highlayer ones. Based on these conclusions, we propose a simple yet effective
self-debiasing framework for Transformer-based NLU models. Concretely, we first
stack a classifier on a selected low layer. Then, we introduce a residual
connection that feeds the low-layer sentence representation to the top-layer
classifier. In this way, the top-layer sentence representation will be trained
to ignore the common biased features encoded by the low-layer sentence
representation and focus on task-relevant unbiased features. During inference,
we remove the residual connection and directly use the top-layer sentence
representation to make predictions. Extensive experiments and indepth analyses
on NLU tasks show that our framework performs better than several competitive
baselines, achieving a new SOTA on all OOD test sets.