  Language model detoxification aims to minimize the risk of generating
offensive or harmful content in pretrained language models (PLMs) for safer
deployment. Existing methods can be roughly categorized as finetuning-based and
decoding-based. However, the former is often resource-intensive, while the
latter relies on additional components and potentially compromises the
generation fluency. In this paper, we propose a more lightweight approach that
enables the PLM itself to achieve "self-detoxification". Our method is built
upon the observation that prepending a negative steering prompt can effectively
induce PLMs to generate toxic content. At the same time, we are inspired by the
recent research in the interpretability field, which formulates the evolving
contextualized representations within the PLM as an information stream
facilitated by the attention layers. Drawing on this idea, we devise a method
to identify the toxification direction from the normal generation process to
the one prompted with the negative prefix, and then steer the generation to the
reversed direction by manipulating the information movement within the
attention layers. Experimental results show that our approach, without any
fine-tuning or extra components, can achieve comparable performance with
state-of-the-art methods.
