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TraCE: Trajectory-Aware Concepts for Explainable Video Understanding

Summary

TraCE is a concept-based framework that discovers source-flexible motion concepts by clustering optical-flow trajectories, maintaining competitive performance on action recognition and video question answering while providing evidence of semantic alignment and decision faithfulness.

SourcearXiv Computer VisionAuthor: Wooil Lee, Junpyo Hong, Jongseo Lee, Tuomas Oikarinen, Tsui-Wei Weng, Jinwoo Choi
TraCE: Trajectory-Aware Concepts for Explainable Video Understanding
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[Submitted on 4 Nov 2026]

Title:TraCE: Trajectory-Aware Concepts for Explainable Video Understanding

View a PDF of the paper titled TraCE: Trajectory-Aware Concepts for Explainable Video Understanding, by Wooil Lee and 5 other authors

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Abstract:Video understanding models often rely on motion, yet their explanations can obscure which motion sources support a prediction. We identify motion-source under-specification as a limitation of existing video XAI: region-centric explanations can be source-ambiguous, while motion vocabularies restricted to single-person pose sequences are source-incomplete. We propose TraCE (Trajectory-Aware Concepts for Explainable Video Understanding), a concept-based framework that discovers source-flexible motion concepts by clustering optical-flow trajectories from training videos. These concepts represent dynamic evidence from people, objects, and interactions, while object and scene concepts account for static context. The resulting typed trajectory/object/scene interface supports class prediction for action recognition and question-conditioned concept matching for video question answering (VQA). We evaluate TraCE across five random seeds on six benchmarks: NTU RGB+D Mutual, Chiral SSv2, UCF-101, KTH, TOMATO, and STAR. Relative to non-interpretable baselines, TraCE maintains competitive task performance, with an average accuracy drop of 1.0 points for action recognition and a nominal gain of 0.4 points for VQA. Motion perturbation and concept-removal tests provide complementary evidence of directional semantic alignment and decision faithfulness, while sample-level interventions illustrate targeted model debugging. Our project page is available at this https URL.

Comments: Accepted to NeurIPS 2026. Project page: this https URL

Subjects:

Computer Vision and Pattern Recognition (cs.CV)

Cite as: arXiv:2611.07009 [cs.CV]

(or arXiv:2611.07009v1 [cs.CV] for this version)

https://doi.org/10.48550/arXiv.2611.07009

arXiv-issued DOI via DataCite (pending registration)

Submission history

From: Wooil Lee [view email] [v1] Wed, 4 Nov 2026 19:00:01 UTC (4,971 KB)

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Key points

  • TraCE discovers source-flexible motion concepts from people, objects, and interactions via optical-flow trajectory clustering
  • Average accuracy drop of only 1.0 point for action recognition and nominal gain of 0.4 points for VQA across six benchmarks
  • Motion perturbation and concept-removal tests demonstrate directional semantic alignment and decision faithfulness
  • Accepted to NeurIPS 2026 with a public project page

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