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One Mask to Rule Them All: On Hidden Facts after Editing and How to Find Them

Summary

A study reveals that knowledge editing methods like ROME and MEMIT share a common mechanism despite fact-specific weight changes. A binary mask trained over edited weights reverses over 70% of edits, indicating a shared functional subspace. The mask works by eliminating overattention in later layers, and injecting it during editing drops success from 98% to 38%. Edits suppress rather than overwrite knowledge, explaining failures to propagate changes. This work aids detection and defense against unwanted edits.

SourcearXiv Machine LearningAuthor: Ali Holmov, Paul Youssef, Nandi Schoots, Christin Seifert
One Mask to Rule Them All: On Hidden Facts after Editing and How to Find Them
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[2605.28839] One Mask to Rule Them All: On Hidden Facts after Editing and How to Find Them

[Submitted on 18 Apr 2026]

Title:One Mask to Rule Them All: On Hidden Facts after Editing and How to Find Them

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Abstract:Knowledge editing methods such as ROME and MEMIT update factual associations in transformer models by modifying MLP weights. While evaluated mainly by output behavior, their internal mechanism remains underexplored. We investigate whether edits rely on a common mechanism, regardless of which fact is modified. Despite fact-specific weight changes, we argue that ROME and MEMIT target the same subset of weights critical for maintaining edits. To isolate this subset, we train a compact binary mask over the edited weights. The mask reverses 80% of edits on the training set and over 70% on the test set, confirming that diverse edits share a common functional structure. Our analysis reveals that the mask reverses edits by eliminating overattention in later layers. Additionally, we show that injecting the mask during editing drops editing success from 98% to 38%, demonstrating that this mechanism is necessary for edits to succeed. Our finding that edits suppress rather than overwrite knowledge explains why ROME and MEMIT fail to propagate changes to related facts. The identified common functional subspace informs detection and defense against unwanted edits.

Comments: Accepted to Findings of ACL 2026

Subjects:

Machine Learning (cs.LG)

Cite as: arXiv:2605.28839 [cs.LG]

(or arXiv:2605.28839v1 [cs.LG] for this version)

https://doi.org/10.48550/arXiv.2605.28839

arXiv-issued DOI via DataCite (pending registration)

Submission history

From: Ali Holmov [view email] [v1] Sat, 18 Apr 2026 16:18:08 UTC (1,244 KB)

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Key points and analysis

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Key points

  • Edits by ROME/MEMIT rely on a common weight subspace, regardless of the fact modified.
  • A compact binary mask can reverse 70%+ of edits by reducing overattention in later layers.
  • Edits suppress rather than overwrite knowledge, preventing propagation to related facts.
  • The discovered subspace enables detection and defense against malicious edits.

Highlights and analysis are generated automatically and may contain errors. Check the original source.