AIM: Anchor Identity Features, Then Match for Multimodal Large Language Model Unlearning

Wonjun Lee, Jaehyuk Jang, Kangwook Ko, Hee-Seon Kim, Changick Kim


Abstract
Multimodal large language models (MLLMs) can memorize identity-specific facts about people in their fine-tuning data, creating privacy risks when a person requests deletion. Existing MLLM unlearning methods often assume access to retain images or ground-truth answers during deletion, which is unrealistic in many practical scenarios. We study identity unlearning when retain images are unavailable at deletion time. Our analysis shows that identity and visual-perception questions occupy distinct regions in fine-tuned hidden states and are organized differently: identity questions cluster by person, whereas perception questions cluster by question type. This suggests that identity knowledge can be suppressed without erasing general visual perception. Building on this observation, we propose AIM, a two-stage method that anchors an identity-forgetting target with a universal visual prompt and then matches the vision encoder to that target under a Fisher-based constraint. Extensive experiments show that AIM achieves competitive identity forgetting while preserving non-deleted identities, prior knowledge, and visual perception on the same images.
Anthology ID:
2026.findings-emnlp.1439
Volume:
Findings of the Association for Computational Linguistics: EMNLP 2026
Month:
October
Year:
2026
Address:
Budapest, Hungary
Editors:
Hung-Yi Lee, Sunipa Dev, Jessy Li, Desmond Elliott
Venue:
Findings
SIG:
SIGDAT
Publisher:
Association for Computational Linguistics
Note:
Pages:
30699–30722
Language:
URL:
https://aclanthology.org/2026.findings-emnlp.1439/
DOI:
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Cite (ACL):
Wonjun Lee, Jaehyuk Jang, Kangwook Ko, Hee-Seon Kim, and Changick Kim. 2026. AIM: Anchor Identity Features, Then Match for Multimodal Large Language Model Unlearning. In Findings of the Association for Computational Linguistics: EMNLP 2026, pages 30699–30722, Budapest, Hungary. Association for Computational Linguistics.
Cite (Informal):
AIM: Anchor Identity Features, Then Match for Multimodal Large Language Model Unlearning (Lee et al., Findings 2026)
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https://aclanthology.org/2026.findings-emnlp.1439.pdf