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Mitigating Intra- and Inter-modal Forgetting in Continual Learning of Unified Multimodal Models
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Identifies inter-modal forgetting in continual instruction tuning of unified multimodal generative models and proposes MoDE, which decouples text (T-MoE LoRA) and image (V-Adapter LoRA) updates with logit-level knowledge distillation on the image adapter.
Problem
Continual instruction tuning of unified multimodal generative models (UMGMs) suffers catastrophic forgetting both within the text modality (intra-modal, understanding tasks) and across modalities (inter-modal, image generation degraded by understanding-task tuning).
Approach
Decouple modality-specific updates with separate LoRA parameter sets (a sparse MoE-LoRA for text tokens and a single LoRA for image tokens) so text-loss gradients do not touch the image adapter, and anchor the image adapter to the frozen pre-trained model via KD on image-token logits.
Key results
- On Chameleon with five VQA/classification tasks, MoDE reaches 33.47% ACC and 25.99% forgetting, versus 32.86% ACC and 30.95% forgetting for CL-MoE, while achieving FID 53.74 close to zero-shot 52.13.
- DualPrompt has the lowest forgetting (6.82%) but only 31.92% ACC, since it learns the hard tasks poorly.
- With Janus-Pro-1B on six tasks, MoDE attains 53.02% ACC and 14.48% forgetting, versus 43.18% and 21.96% for CL-MoE.
Measured effects reported in the paper
| What was changed | Where | Measured | Effect |
|---|---|---|---|
| Replace modality-coupled continual learning with MoDE | Chameleon · Continual multimodal understanding | Accuracy: 33.01 -> 33.47 | Helped |
| Replace modality-coupled continual learning with MoDE | Chameleon · Image generation | FID: 65.16 -> 53.74 | Helped |
| Add knowledge distillation to the V-Adapter (ablation) | MoDE on Chameleon · Image generation | FID: 54.61 -> 53.74 | Helped |
| Add knowledge distillation to the V-Adapter (ablation) | MoDE on Chameleon · Continual multimodal understanding | Accuracy: 33.07 -> 33.47 | Helped |
| Add the V-Adapter to T-MoE LoRA (ablation) | MoDE on Chameleon · Continual multimodal understanding | Accuracy: 33.03 -> 33.47 | Helped |
| Add 6 rather than 4 T-MoE experts (ablation) | MoDE on Chameleon · Continual multimodal understanding | Accuracy: 33.47 -> 34.90 | Helped |
| Add 6 rather than 4 T-MoE experts (ablation) | MoDE on Chameleon · Image generation | FID: 53.74 -> 52.69 | Helped |
| Increase the KD coefficient from 0.3 to 0.5 (ablation) | MoDE on Chameleon · Image generation | FID: 53.74 -> 53.12 | Helped |
| Increase the KD coefficient from 0.3 to 0.5 (ablation) | MoDE on Chameleon · Continual multimodal understanding | Accuracy: 33.47 -> 31.53 | Hurt |
| Increase the KD coefficient from 0.3 to 1.0 (ablation) | MoDE on Chameleon · Image generation | FID: 53.74 -> 51.72 | Helped |
| Increase the KD coefficient from 0.3 to 1.0 (ablation) | MoDE on Chameleon · Continual multimodal understanding | Accuracy: 33.47 -> 32.10 | Hurt |
| Add KD to Seq LoRA (ablation) | Seq LoRA on Chameleon · Continual multimodal learning | Accuracy: 28.43 -> 30.81 | Helped |
Surprising findings
- Adding knowledge distillation to coupled baselines (MoELoRA, CL-MoE) reduces visual generation forgetting but hurts understanding accuracy, showing KD alone is insufficient without modality decoupling.
- DualPrompt's low forgetting figure is misleading because it barely learns new tasks (ImageNet best accuracy 24.55%).
Limitations
- Chameleon original checkpoints are unavailable, so a community reimplementation is used.
- Evaluation covers only a small set of tasks and sequences, with image generation measured by CLIP-based scores and FID on CustomConcept101.
- Key theoretical claim relies on a first-order orthogonality argument that holds only by construction of disjoint parameter blocks, and the reported cosine analysis is for the specific setup.
Experimental setup
Datasets: ScienceQA TextVQA GQA VizWiz ImageNet LAION-5B RefCOCO RefCOCO+ RefCOCOg CustomConcept101
Benchmarks: ScienceQA TextVQA GQA VizWiz ImageNet CustomConcept101 RefCOCO RefCOCO+ RefCOCOg
Metrics: accuracy average forgetting CLIP image alignment CLIP text alignment FID
Baselines: Seq LoRA Model Tailor DualPrompt MoELoRA CL-MoE Joint Training
Builds on: LoRA MoELoRA CL-MoE Model Tailor DualPrompt
Closest papers by meaning
- Quantifying Cross-Modality Memorization in Vision-Language Models (NeurIPS 2025 · similarity 0.89)
- Do More Modalities Always Help? A Geometric Perspective on Missing-Modality Robustness (NeurIPS 2026 · similarity 0.88)
- A Closer Look at Multimodal Representation Collapse (ICML 2025 · similarity 0.87)
- Wings: Learning Multimodal LLMs without Text-only Forgetting (NeurIPS 2024 · similarity 0.87)
- Concurrent Image Understanding and Generation: Self-Correcting Coupled Markov Jump Process (NeurIPS 2026 · similarity 0.87)
- Dynamic Cross-Modal Prompt Generation for Multimodal Continual Instruction Tuning (NeurIPS 2026 · similarity 0.87)
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