Metric Sentiment Learning for Label Representation

Label representation aims to generate a so-called verbalizer to an input text, which has a broad application in the field of text classification, event detection, question answering, etc. Previous works on label representation, especially in a few-shot setting, mainly define the verbalizers manually, which is accurate but time-consuming. Other models fail to correctly produce antonymous verbalizers for two semantically opposite classes. Thus, in this paper, we propose a metric sentiment learning framework (MSeLF) to generate the verbalizers automatically, which can capture the sentiment differences between the verbalizers accurately. In detail, MSeLF consists of two major components, i.e., the contrastive mapping learning (CML) module and the equal-gradient verbalizer acquisition (EVA) module. CML learns a transformation matrix to project the initial word embeddings to the antonym-aware embeddings by enlarging the distance between the antonyms. After that, in the antonym-aware embedding space, EVA first takes a pair of antonymous words as verbalizers for two opposite classes and then applies a sentiment transition vector to generate verbalizers for intermediate classes. We use the generated verbalizers for the downstream text classification task in a few-shot setting on two publicly available fine-grained datasets. The results indicate that our proposal outperforms the state-of-the-art baselines in terms of accuracy. In addition, we find CML can be used as a flexible plug-in component in other verbalizer acquisition approaches.