By drawing inspiration from the computer vision domain, contrastive learning has emerged as another paradigm for unsupervised sentence embedding. By using contrastive learning, most recent sentence embedding methods have achieved promising results. However, previous methods focused on constructing positive and negative pairs through traditional data augmentation, which was unable to balance the loss of semantics and the additional features brought by aggressive data augmentation. In the present study, we propose a prototype contrastive learning framework based on a distribution divergence minimization loss function and introduce the concept of strong semantic prototypes. Specifically, with the aid of prompts, our method constructs three semantic prototypes for each instance: a basic semantic prototype, a strong semantic prototype and a negative prototype. By combining InfoNCE loss with distribution divergence minimization loss, Contrastive Learning of Sentence Embedding with Strong Semantic Prototypes (CLSESSP) creates another optimization objective that integrates strong augmentation. The experiments conducted on the semantic text similarity (STS) datasets demonstrate that the proposed CLSESSP surpasses the strong baseline by an average of 2.9 points in the BERT-base model. Extensive experimental results on transfer and clustering tasks demonstrate the effectiveness of our proposed model compared to strong baselines. The code is available at https://github.com/KCshen1125/CLSESSP.
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