On the duality between contrastive and non-contrastive self-supervised learning
This work provides a unifying theoretical framework for self-supervised learning, which is incremental but important for advancing the field by clarifying relationships between existing methods.
The paper tackles the problem of understanding the theoretical similarities between contrastive and non-contrastive self-supervised learning methods, showing that they can be equivalent under limited assumptions and that performance gaps can be closed with better hyperparameter tuning, such as improving SimCLR to match VICReg's performance.
Recent approaches in self-supervised learning of image representations can be categorized into different families of methods and, in particular, can be divided into contrastive and non-contrastive approaches. While differences between the two families have been thoroughly discussed to motivate new approaches, we focus more on the theoretical similarities between them. By designing contrastive and covariance based non-contrastive criteria that can be related algebraically and shown to be equivalent under limited assumptions, we show how close those families can be. We further study popular methods and introduce variations of them, allowing us to relate this theoretical result to current practices and show the influence (or lack thereof) of design choices on downstream performance. Motivated by our equivalence result, we investigate the low performance of SimCLR and show how it can match VICReg's with careful hyperparameter tuning, improving significantly over known baselines. We also challenge the popular assumption that non-contrastive methods need large output dimensions. Our theoretical and quantitative results suggest that the numerical gaps between contrastive and non-contrastive methods in certain regimes can be closed given better network design choices and hyperparameter tuning. The evidence shows that unifying different SOTA methods is an important direction to build a better understanding of self-supervised learning.