Towards Better Understanding of Contrastive Sentence Representation Learning: A Unified Paradigm for Gradient
This addresses a theoretical gap for NLP researchers by explaining performance differences in sentence representation learning, though it appears incremental as it builds on existing contrastive and non-contrastive SSL methods.
The paper tackled the problem of understanding why contrastive self-supervised learning outperforms non-contrastive methods in sentence representation ranking tasks like Semantic Textual Similarity, and discovered a unified gradient paradigm with three components that, when adjusted, enabled non-contrastive methods to achieve outstanding performance in STS.
Sentence Representation Learning (SRL) is a crucial task in Natural Language Processing (NLP), where contrastive Self-Supervised Learning (SSL) is currently a mainstream approach. However, the reasons behind its remarkable effectiveness remain unclear. Specifically, many studies have investigated the similarities between contrastive and non-contrastive SSL from a theoretical perspective. Such similarities can be verified in classification tasks, where the two approaches achieve comparable performance. But in ranking tasks (i.e., Semantic Textual Similarity (STS) in SRL), contrastive SSL significantly outperforms non-contrastive SSL. Therefore, two questions arise: First, *what commonalities enable various contrastive losses to achieve superior performance in STS?* Second, *how can we make non-contrastive SSL also effective in STS?* To address these questions, we start from the perspective of gradients and discover that four effective contrastive losses can be integrated into a unified paradigm, which depends on three components: the **Gradient Dissipation**, the **Weight**, and the **Ratio**. Then, we conduct an in-depth analysis of the roles these components play in optimization and experimentally demonstrate their significance for model performance. Finally, by adjusting these components, we enable non-contrastive SSL to achieve outstanding performance in STS.