Mixture of Probes: Learning from Privileged Modalities in Multimodal LLMs Through Probing
This paper introduces Mixture of Probes (MoP), a framework that enables multimodal LLMs to effectively leverage auxiliary modalities only available during training. MoP uses a structured probing mechanism to extract information from intermediate representations, and MoP-X training strategy with probe disentanglement loss. Experiments show up to 65% relative improvement over baselines.
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[Submitted on 9 Jul 2026]
Title:Mixture of Probes: Learning from Privileged Modalities in Multimodal LLMs Through Probing
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Abstract:Multimodal Large Language Models (MLLMs) are typically designed under the assumption that all modalities available during training will also be accessible at inference. However, many real-world settings violate this assumption, requiring models to operate under a privileged modality setting, where auxiliary modalities are available only during training. While these modalities contain valuable information, existing MLLMs largely fail to leverage them effectively, as they treat modalities as interchangeable inputs rather than sources of complementary supervision. We propose Mixture of Probes (MoP), a novel framework that disentangles modality-specific and modality-general signals within the MLLM, allowing the model to preserve modality-dependent structure while learning transferable representations across modalities. At its core, MoP achieves this through a structured probing mechanism that extracts and organizes information from intermediate representations of a shared modality encoder, rather than relying only on final-layer alignment as done in existing MLLMs. To support this disentanglement, we further introduce MoP Cross-modal Training (MoP-X), a training strategy for MoP centered around a probe disentanglement loss that prevents probe collapse and encourages cross-modal learning. We evaluate MoP across two domains spanning eight tasks and four modalities under a comprehensive evaluation protocol tailored to the privileged modality setting, where each modality is independently treated as the sole input at inference time. MoP consistently outperforms strong MLLM baselines, achieving up to 65% relative improvement, demonstrating that auxiliary modalities, even when unavailable at inference, can provide substantial gains when effectively leveraged during training. Code, model checkpoints, and evaluation protocols will be made available at this https URL.
Comments: Preprint (16 pages)
Subjects:
Computer Vision and Pattern Recognition (cs.CV); Machine Learning (cs.LG)
Cite as: arXiv:2607.08839 [cs.CV]
(or arXiv:2607.08839v1 [cs.CV] for this version)
https://doi.org/10.48550/arXiv.2607.08839
arXiv-issued DOI via DataCite
Submission history
From: Dominick Reilly [view email] [v1] Thu, 9 Jul 2026 18:00:47 UTC (1,188 KB)
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