Time-Series Contrastive Learning Against False Negatives and Class Imbalance

Self-supervised contrastive learning (SCL) has driven significant advancements in time-series representation learning. While recent studies built upon the information noise contrastive estimation (InfoNCE) loss framework focus on constructing appropriate positives and negatives, we theoretically analyze and identify two overlooked issues inherent in this approach: false negatives and class imbalance. To address these challenges, we propose a simple yet effective modification based on the SimCLR framework, integrating a multi-instance discrimination task to mitigate false negatives. Additionally, we introduce a graph-based interactive projection head and semantic consistency regularization, which enhances minority-class representations with minimal annotation cost. Extensive experiments on six real-world time-series datasets demonstrate that our approach consistently outperforms state-of-the-art methods, achieving up to 3.96% higher accuracy and 10.73% improvement in $F1$ -score, particularly benefiting imbalanced data scenarios.