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PARC: A Quantitative Framework Uncovering the Symmetries within Vision Language Models
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Introduces PARC, a framework that measures VLM prompt sensitivity using 11 language and vision prompt variations, a calibrated reliability score with guarantees, and calibration against random-guess performance, evaluating 22 VLMs across 7 MC-VQA datasets.
Problem
VLMs are sensitive to prompt changes, but existing studies use only noisy corruptions, rely on multiple non-comparable scores, and cannot compare results across datasets or prompt variations with different random-guess baselines.
Approach
Mirror LLM prompt variation classes (reformulations and semantic changes) in both language and vision, combine accuracy and conformal-prediction certainty into one reliability score with explicit guarantees, and rescale all metrics relative to expected random performance so they are comparable across datasets and prompts.
Key results
- Across 22 VLMs, language negation with antonyms (LS-A) and image exchanges (VS-E) nearly reduce calibrated consistency to random (~0), while reformulations are tolerated better than semantic changes.
- InternVL2-40B is the most reliable and consistent model overall, with InternVL2 family models outperforming other families at matched LLM sizes.
- Reliability and calibrated consistency are positively correlated across models and datasets, and calibration reverses accuracy orderings on MMBench (e.g., LS-N vs. O).
Measured effects reported in the paper
| What was changed | Where | Measured | Effect |
|---|---|---|---|
| Use semantic prompt changes instead of reformulations, which alter the expected answer | VLMs evaluated with PARC · Comparative datasets and MMBench | calibrated consistency | Hurt |
| Use verbose language reformulations instead of the original prompt | 22 evaluated VLMs · 7-dataset average | calibrated reliability: 0.29 -> 0.21 | Hurt |
| Negate the language prompt | 22 evaluated VLMs · 7-dataset average | calibrated reliability: 0.29 -> 0.17 | Hurt |
| Substitute antonyms in the language prompt | 22 evaluated VLMs · 7-dataset average | calibrated reliability: 0.29 -> 0.10 | Hurt |
| Brighten the image | 22 evaluated VLMs · 7-dataset average | calibrated reliability: 0.29 -> 0.21 | Hurt |
| Exchange the correct image for an incorrect one | 22 evaluated VLMs · 6 comparative datasets | calibrated reliability: 0.29 -> 0.13 | Hurt |
| Swap the two images | 22 evaluated VLMs · 6 comparative datasets | calibrated reliability: 0.29 -> 0.29 | No clear effect |
| Use InternVL2 models rather than other evaluated model families | VLMs evaluated with PARC · 7-dataset average | calibrated reliability | Helped |
| Increase model size within a model family | VLMs evaluated with PARC · 7-dataset average | calibrated reliability | Helped |
| Train on more high-quality, curated data | VLMs evaluated with PARC · 7-dataset average | calibrated reliability | Helped |
Surprising findings
- Image swaps (VS-S) improved average accuracy and reliability, suggesting model confusion toward spatial arrangement.
- Model family is a better predictor of reliability than model size; InternVL2-2B is on par with LLaVA-1.5 13B.
Limitations
- Framework targets white-box VLMs because certainty requires softmax scores, so black-box models are not directly analyzed.
- Limited to multiple-choice VQA; generative tasks would need extra LLM judges.
- Only one semantic vision variation (exchange) fewer than other variations due to cost of photo-realistic edits.
Experimental setup
Datasets: MMBench MIT-States MIT-Attributes VAW-States VAW-Attributes NYU-Depth V2 Fashionpedia
Benchmarks: MMBench MIT-States MIT-Attributes VAW-States VAW-Attributes NYU-Depth V2 Fashionpedia
Metrics: accuracy certainty consistency reliability calibrated scores
Baselines: LLaVA-1.5 LLaVA-1.6 Qwen-VL CogVLM CogVLM2 InternVL2 Cambrian
Builds on: conformal prediction CompBench MMBench
Closest papers by meaning
- VHELM: A Holistic Evaluation of Vision Language Models (NeurIPS 2024 · similarity 0.91)
- SPA-VL: A Comprehensive Safety Preference Alignment Dataset for Vision Language Models (CVPR 2025 · similarity 0.90)
- VP-Bench: A Comprehensive Benchmark for Visual Prompting in Multimodal Large Language Models (AAAI 2026 · similarity 0.90)
- Prismatic VLMs: Investigating the Design Space of Visually-Conditioned Language Models (ICML 2024 · similarity 0.90)
- Language Models as Black-Box Optimizers for Vision-Language Models (CVPR 2024 · similarity 0.90)
- Amend to Alignment: Decoupled Prompt Tuning for Mitigating Spurious Correlation in Vision-Language Models (ICML 2024 · similarity 0.90)
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