Multi-Instance Multi-Label Learning for Text-motion Retrieval

Text-motion retrieval (TMR) is a significant cross-modal task that retrieves motion sequences semantically similar to a given query text. Existing TMR methods primarily utilize single embeddings to represent and align text and motion sequences. However, real-world motion sequences typically contain multiple atomic motions with complex semantics, which is hard to precisely capture by single embeddings. Additionally, the common co-occurring and coupling of atomic motions further post significant challenges in effective modeling and aligning text and motion sequences. In this paper, we regard TMR as a Multi-Instance Multi-Label (MIML) learning problem, where the motion sequence is viewed as a bag of atomic motions and the text is the bag of corresponding phrases. To address the MIML problem, we propose a novel Multi-Granularity Semantics Interaction (MGSI) approach, which effectively captures and aligns the semantics of text and motion sequences across various levels. Specifically, the MGSI approach initially decomposes both the query and motion sequences into three hierarchical levels: token, instance, and bag. Then, we utilize graph neural networks to explicitly model their semantics correlation and perform semantics interaction at these respective levels, precisely capturing the semantics at multiple granularities. To identify and model co-occurring atomic motions, we measure the frame-wise semantic consistency between motions and then fuse and interact the accordant ones to refine their representations. Finally, we exploit token, instance, and bag-wise semantics interaction to comprehensively align text and motion sequence. We evaluated our methods on two widely-used benchmark datasets, HumanML3D and KIT-ML. The proposed method achieves significant improvements, outperforming the state-of-the-art with a 23.09% increase in Rsum on HumanML3D and a 21.84% increase on KIT-ML.