With the development of neural topic models in recent years, topic modelling is playing an increasingly important role in natural language understanding. However, most existing topic models still rely on bag-of-words (BoW) information, either as training input or training target. This limits their ability to capture word order information in documents and causes them to suffer from the out-of-vocabulary (OOV) issue, i.e. they cannot handle unobserved words in new documents. Contextualized word embeddings from pre-trained language models show superiority in the ability of word sense disambiguation and prove to be effective in dealing with OOV words. In this work, we developed a novel neural topic model combining contextualized word embeddings from the pre-trained language model BERT. The model can infer the topic distribution of a document without using any BoW information. In addition, the model can infer the topic distribution of each word in a document directly from the contextualized word embeddings. Experiments on several datasets show that our model outperforms existing topic models in terms of both document classification and topic coherence metrics and can accommodate unseen words from newly arrived documents. Experiments on the NER dataset also show that our model can produce high-quality word topic representations.

本研究开发了一种新型的神经主题模型，结合了来自预先训练的语言模型BERT的上下文化单词嵌入，无需使用任何词袋信息即可推断文档的主题分布，实验表明该模型在文档分类和主题连贯度指标方面优于现有主题模型，并可处理来自新到达文档的未见单词。

BERTTM：利用预训练语言模型的上下文化单词嵌入来进行神经主题建模