Nonparametric Clustering-Guided Cross-View Contrastive Learning for Partially View-Aligned Representation Learning

With the increasing availability of multi-view data, multi-view representation learning has emerged as a prominent research area. However, collecting strictly view-aligned data is usually expensive, and learning from both aligned and unaligned data can be more practicable. Therefore, Partially View-aligned Representation Learning (PVRL) has recently attracted increasing attention. After aligning multi-view representations based on their semantic similarity, the aligned representations can be utilized to facilitate downstream tasks, such as clustering. However, existing methods may be constrained by the following limitations: 1) They learn semantic relations across views using the known correspondences, which is incomplete and the existence of false negative pairs (FNP) can significantly impact the learning effectiveness; 2) Existing strategies for alleviating the impact of FNP are too intuitive and lack a theoretical explanation of their applicable conditions; 3) They attempt to find FNP based on distance in the common space and fail to explore semantic relations between multi-view data. In this paper, we propose a Nonparametric Clustering-guided Cross-view Contrastive Learning (NC3L) for PVRL, in order to address the above issues. Firstly, we propose to estimate the similarity matrix between multi-view data in the marginal cross-view contrastive loss to approximate the similarity matrix of supervised contrastive learning (CL). Secondly, we establish the theoretical foundation for our proposed method by analyzing the error bounds of the loss function and its derivatives between our method and supervised CL. Thirdly, we propose a Deep Variational Nonparametric Clustering (DeepVNC) by designing a deep reparameterized variational inference for Dirichlet process Gaussian mixture models to construct cluster-level similarity between multi-view data and discover FNP. Additionally, we propose a reparameterization trick to improve the robustness and the performance of our proposed CL method. Extensive experiments on four widely used benchmark datasets show the superiority of our proposed method compared with state-of-the-art methods.