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arxiv: 2604.23112 · v1 · submitted 2026-04-25 · 💻 cs.LG

Recognition: unknown

Conditional Imputation for Within-Modality Missingness in Multi-Modal Federated Learning

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Pith reviewed 2026-05-08 08:27 UTC · model grok-4.3

classification 💻 cs.LG
keywords multimodal federated learningconditional imputationdiffusion modelswithin-modality missingnessclinical datadata imputationfederated learning
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The pith

Conditional diffusion models impute missing multimodal data to let federated models train on complete records.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The paper introduces CondI, a federated learning approach that explicitly imputes unobserved temporal segments in multimodal clinical data instead of relying on implicit embeddings or alignments. It uses conditional diffusion models guided by available context and embeddings in a first phase, then trains modality-specific extractors and joint spaces on the filled data. This produces holistic representations for downstream tasks even when sensors drop out irregularly. On three clinical datasets the method matches existing baselines while showing greater tolerance for high missingness rates.

Core claim

Explicit imputation of missing within-modality components via conditional diffusion models recovers the true underlying distribution and lets the model operate on complete semantic structures, which in turn increases resilience to severe data incompleteness during both training and inference in privacy-preserving multimodal federated settings.

What carries the argument

CondI two-phase pipeline in which conditional diffusion models first impute missing temporal components from multimodal context and conditional embeddings, after which modality-specific extractors and joint embedding spaces are optimized on the completed data.

If this is right

  • Imputed raw data pass through the trained extractors to produce robust features that support joint embedding spaces.
  • Performance remains comparable to state-of-the-art methods even under severe within-modality missingness on clinical datasets.
  • Privacy-preserving collaborative training becomes feasible for applications with intermittent sensors or irregular sampling.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

  • The same explicit-imputation step could be inserted into other federated architectures to reduce reliance on architectural alignment tricks.
  • If future diffusion models achieve higher fidelity, the resilience to missingness could extend to even higher rates or longer gaps.
  • Testing the framework on non-clinical multimodal streams with similar intermittency patterns would clarify whether the benefit is domain-specific.

Load-bearing premise

Conditional diffusion models can accurately recover the true underlying distribution of missing temporal components from the available multimodal context and embeddings.

What would settle it

An experiment in which imputed values are generated from held-out complete samples and then compared to the actual observed values; large statistical divergence between the two distributions, or no performance gain over implicit baselines at high missingness rates, would falsify the central claim.

Figures

Figures reproduced from arXiv: 2604.23112 by Chen Chen, Katie Wang, Song Wang, Wugeng Zheng, Ziwen Kan.

Figure 1
Figure 1. Figure 1: Overview of the proposed CondI framework. (a) Global Federated Workflow. The server coordinates the distribution and view at source ↗
Figure 2
Figure 2. Figure 2: Detailed architecture of the Conditional Diffusion mod view at source ↗
Figure 3
Figure 3. Figure 3: Per-sample feature reconstruction quality. Each point view at source ↗
read the original abstract

Multimodal Federated Learning (MMFL) enables privacy-preserving collaborative training, but real-world clinical applications often suffer from within-modality missingness caused by sensor intermittency or irregular sampling. Existing methods implicitly represent unobserved data via architectural alignment or missing embeddings, often failing to recover the true distribution and yielding sub-optimal performance. We propose CondI, a federated framework explicitly addressing this missingness using conditional diffusion models. CondI employs a two-phase training pipeline: first, imputing unobserved temporal components using available multimodal context and conditional embeddings; second, optimizing modality-specific extractors and joint embedding spaces. During inference, imputed raw data pass through trained extractors to generate robust features, providing a holistic representation for downstream tasks. Explicit data imputation ensures models operate on complete semantic structures, significantly enhancing resilience against severe data incompleteness. Experiments on three clinical datasets (PTB-XL, SLEEP-EDF, MIMIC-IV) demonstrate CondI achieves comparable results to state-of-the-art baselines. Code: https://github.com/ZhengWugeng/CondI

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Referee Report

2 major / 0 minor

Summary. The paper proposes CondI, a multimodal federated learning framework that explicitly imputes within-modality missing temporal data using conditional diffusion models conditioned on available multimodal context and embeddings. It describes a two-phase pipeline (imputation followed by extractor and joint embedding optimization) and claims that operating on complete semantic structures via explicit imputation significantly enhances resilience to severe missingness. Experiments on PTB-XL, SLEEP-EDF, and MIMIC-IV are reported to yield performance comparable to state-of-the-art baselines, with code released at https://github.com/ZhengWugeng/CondI.

Significance. If the central claim of meaningful improvement in resilience holds under detailed scrutiny, the work would address a practical gap in clinical MMFL where sensor intermittency causes within-modality missingness; explicit imputation could outperform implicit embedding approaches. The release of reproducible code is a clear strength that supports verification and extension.

major comments (2)
  1. [Abstract] Abstract: the central claim that explicit imputation 'significantly enhancing resilience against severe data incompleteness' is not supported by the stated results, which report only that CondI 'achieves comparable results to state-of-the-art baselines' with no quantitative deltas, missing-rate sweeps, error bars, statistical tests, or ablation details on downstream performance under varying incompleteness levels.
  2. [Method] Method description: the two-phase pipeline and conditional diffusion imputation step are presented without equations, loss formulations, or conditioning details (e.g., how multimodal embeddings are injected into the diffusion process), making it impossible to assess whether the model can recover the true underlying distribution as assumed.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for the constructive feedback on our manuscript. The comments highlight important areas for improving clarity and supporting claims with evidence. We address each major comment below and commit to revisions that strengthen the presentation without altering the core contributions.

read point-by-point responses
  1. Referee: [Abstract] Abstract: the central claim that explicit imputation 'significantly enhancing resilience against severe data incompleteness' is not supported by the stated results, which report only that CondI 'achieves comparable results to state-of-the-art baselines' with no quantitative deltas, missing-rate sweeps, error bars, statistical tests, or ablation details on downstream performance under varying incompleteness levels.

    Authors: We agree that the abstract as currently worded does not sufficiently substantiate the claim of significant enhancement with quantitative details. The experiments section of the manuscript reports results across PTB-XL, SLEEP-EDF, and MIMIC-IV under multiple missingness rates, including comparisons to baselines, but these specifics are not summarized in the abstract. In the revision, we will update the abstract to include key quantitative deltas, missing-rate performance trends, and references to statistical comparisons where available, ensuring the claim is directly supported by the reported evidence. revision: yes

  2. Referee: [Method] Method description: the two-phase pipeline and conditional diffusion imputation step are presented without equations, loss formulations, or conditioning details (e.g., how multimodal embeddings are injected into the diffusion process), making it impossible to assess whether the model can recover the true underlying distribution as assumed.

    Authors: The referee correctly identifies that the method description lacks the necessary mathematical formalization. The current manuscript outlines the two-phase pipeline at a high level but does not provide the diffusion process equations, the training objective (such as the conditional denoising loss), or the precise mechanism for injecting multimodal embeddings and context as conditioning signals. We will revise the method section to include these details, including the forward and reverse diffusion steps, the loss formulation, and the conditioning injection strategy, allowing readers to evaluate the distributional recovery assumptions. revision: yes

Circularity Check

0 steps flagged

No circularity: descriptive pipeline with no equations or self-referential reductions

full rationale

The manuscript describes a two-phase federated framework (CondI) that first imputes missing temporal components via conditional diffusion models and then optimizes extractors, but supplies no mathematical derivations, equations, or 'predictions' that reduce to fitted inputs by construction. The abstract and available text contain no self-definitional steps, no fitted parameters renamed as predictions, and no load-bearing self-citations that justify uniqueness theorems. Experimental claims rest on reported performance on PTB-XL, SLEEP-EDF and MIMIC-IV rather than on any internal tautology. The derivation chain is therefore self-contained and non-circular.

Axiom & Free-Parameter Ledger

0 free parameters · 0 axioms · 0 invented entities

Based solely on the abstract, no explicit free parameters, axioms, or invented entities are detailed; the approach implicitly relies on standard assumptions of diffusion models being able to model conditional distributions from multimodal context.

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discussion (0)

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