REVIEW 5 major objections 5 minor 16 references
Drawing the Line: Enhancing Trustworthiness of MLLMs Through the Power of Refusal
T0 review · 5 major / 5 minor · reviewed 2026-08-11 · deepseek-v4-flash
Pith's one-line read The paper claims that teaching MLLMs to refuse questions outside their information boundaries sharply improves trustworthiness without sacrificing helpfulness.
desk verdict Table 2 contradicts Eq. (5), so the headline trustworthiness gain is unverified; the framework and OOD results are promising enough to send to review with major-revision demands. read the letter →
The pith
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
The reading
What carries the argument
The central object is a pair of information boundaries: the extrinsic boundary, which asks whether the needed information is present in the visual input, and the intrinsic boundary, which asks whether this particular model's knowledge and perceptual capacity can supply the answer. Confidence estimation locates the intrinsic boundary by sampling multiple responses from the base model and measuring the accuracy rate with a hybrid evaluator (string matching plus an LLM semantic check), then splitting questions into Known, Mixed, and Unknown using thresholds $\delta_k$ and $\delta_{uk}$. The training machinery is Confidence-aware DPO, a loss that weights two preference pairs - 'correct over incorrect' and 'refusal over incorrect' - by the estimated confidence $conf_x$, so high-confidence questions push toward answering and low-confidence ones push toward refusal. The evaluation machinery is a user-centric trustworthiness score $s_{trust} = 2\cdot Acc + RefR - 1$, which rewards correct answers, rewards refusals over wrong ones, and lets different models be compared without knowing each model's boundary.
What would settle it
Give the pipeline a model whose confidence is demonstrably miscalibrated on a controlled topic (for example, images modified so that answerability changes while the question text stays identical), and check where IDK-IT and CA-DPO draw the refusal boundary; if refusals track the biased confidence rather than true answerability, the learned boundary is an artifact of the estimate. A cheaper check on the quantitative claim: recompute the in-domain trustworthiness scores from the reported Acc and RefR values with the paper's own formula $s_{trust} = 2\cdot Acc + RefR - 1$, since the published in-domain numbers do not reproduce and the magnitude of the gain should be re-verified with the released evaluation code or per-sample scores.
Extended reading notes
Core claim
The paper's central claim is that an MLLM should refuse exactly when a question crosses either of two information boundaries, and that this refusal behavior is learnable from the model's own signals. The extrinsic boundary separates questions answerable from the image from those that are not, such as questions about absent objects or false premises; the intrinsic boundary separates what the model's own knowledge and perception can supply from what they cannot. The paper claims that both boundaries can be taught with data generated from any VQA set: confidence estimation for the intrinsic side and GPT-4o-generated unanswerable questions for the extrinsic side. The reported evidence is that IDK-IT and especially the confidence-aware DPO variant (CA-DPO) raise the trustworthiness score above baselines on every benchmark tested, with CA-DPO preserving accuracy while boosting refusal, for example lifting LLaVA1.5-7B's in-domain trustworthiness from -6.50 to 28.50 at a 49.1% refusal rate.
Load-bearing premise
The framework rests on the assumption that the accuracy of the base model's sampled outputs, judged by a hybrid string-matching-plus-LLM checker, truthfully measures whether the model can answer the question; if that estimate is biased, the learned refusal boundary is trained at the wrong place.
Editorial extensions
If this is right
- Training with IDK-IT and CA-DPO raises the trustworthiness score on all out-of-domain benchmarks tested (general VQA, knowledge-intensive VQA, and unanswerable VQA) for both LLaVA1.5-7B and 13B, so the effect is not confined to the training distribution.
- Trained models refuse more on low-confidence questions and answer more on high-confidence ones, and their accuracy on the questions they do answer exceeds the original model's, indicating that boundary awareness improves both caution and usefulness.
- On unanswerable out-of-domain sets (VizWiz-unanswerable, filtered VQAv2-IDK, BeyondVisQA), refusal rates jump from single digits to roughly 70-81%, showing the model can recognize the extrinsic boundary.
- CA-DPO outperforms plain DPO trained on the same preference data, implying that the confidence-weighted balancing is what drives the improvement rather than the preference data alone.
- The data-generation pipeline works with an open-source generator (Qwen2-VL-72B) as well as GPT-4o, so the framework does not depend on a closed API.
Reading between the lines
- The paper does not spell out that the refusal boundary is per-model: applying InBoL to a different base model requires regenerating the IDK data with that model's own confidence estimates, so the framework transfers as a procedure, not as a fixed refusal line.
- A natural extension of the linear-probing result is to condition generated refusals on whether the missing information is visual or knowledge-based, and to score the resulting explanations with the same user-centric metric; the paper lists such explanatory refusals as future work.
- Because the CA-DPO loss weights the answer-versus-refusal trade-off through a single confidence factor, varying that factor should produce a predictable monotone sweep of helpfulness against caution, which would let deployers set the refusal threshold to the cost of error in their application.
- The framework's ceiling is set by the calibration of the sampling-based confidence estimate; replacing it with a calibrated uncertainty measure (ensembles, logit-based tests) would be a direct upgrade path that the paper does not explore.
Signed reviews
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The paper proposes InBoL, an information-boundary-aware learning framework for multimodal large language models (MLLMs) that trains models to refuse answering when information is insufficient. The framework introduces a data construction pipeline that labels training questions as known, mixed, or unknown based on a confidence estimate derived from the base model's sampled-response accuracy, and then applies IDK instruction tuning (IDK-IT) and confidence-aware direct preference optimization (CA-DPO). The paper also proposes a user-centric trustworthiness score, strust = 2*Acc + RefR - 1, and evaluates it on in-domain and out-of-domain datasets with LLaVA1.5-7B/13B, claiming significant trustworthiness improvements while preserving helpfulness.
Significance. If the reported gains are reliable, the paper addresses an important problem in MLLM trustworthiness by systematically combining refusal behavior with confidence-aware training. The proposed hybrid evaluator (string matching plus LLM judgment) is validated against human annotations with Cohen's Kappa 0.885, which is a useful practical contribution. The data-generation pipeline is shown to work with an open-source model (Qwen2-VL) as well as GPT-4o, enhancing reproducibility. However, the central experimental claim is undermined by an internal inconsistency in the main in-domain results table, which prevents the reader from verifying the reported trustworthiness scores.
major comments (5)
- [Table 2 and Eq. (5)]
- [Table 4 vs Table 2]
- [Section 3.2 and Figure 4]
- [Section 5.5]
- [Appendix E and Section 4.2]
minor comments (5)
- [Section 3.1]
- [Throughout]
- [Section 3.2]
- [Tables 5 and 6]
- [Section 2.2]
Circularity Check
Evaluation-loop reductions: the self-awareness curve reuses the confidence signal that built the training labels, and the headline configuration was selected by maximizing the reported trustworthiness metric; the central OOD results remain independent.
-
fitted input called prediction
[Section 3.2 (Estimating the Model's Confidence), Eq. (7) (CA-DPO loss), Section 5.3 (Awareness of the Intrinsic Information Boundary), Figure 4(a)]
"we sample multiple responses from the original model and calculate the accuracy rate to estimate its confidence. ... we analyze changes in the refusal rates of both IDK-IT and CA-DPO models relative to the confidence levels of LLaVA1.5-7B ... The results indicate that the model exhibits an awareness of its own confidence, effectively refusing to answer when appropriate."
Section 3.2 uses the base model's sampled-response accuracy as the confidence signal, then thresholds δk/δuk convert that signal into Known/Mixed/Unknown training labels; Eq. (7) then trains with weight conf on the 'answer' preference and (1−conf) on the 'refuse' preference. Section 5.3 bins the same base-model confidence scores and reports that trained models refuse more at low confidence, calling this 'awareness of its own confidence.' The correlation is the training objective itself, not an independent observation: the model was explicitly trained to map low-confidence inputs to refusal. The analysis therefore does not provide separate evidence for intrinsic self-awareness; it restates the construction of the data and loss.
-
fitted input called prediction
[Appendix F.1 (Confidence threshold), Appendix F.2 (Data Composition), Tables 1–2]
"We conducted experiments to analyze the impact of the confidence thresholds δk and δuk. Both thresholds were varied within the range δk, δuk ∈ {2, 3, 4, 5, 6, 7, 8}, ensuring that δk > δuk. ... the combination of δk = 8 and δuk = 2 yields the best performance. ... As shown in Figure 11(b), the optimal trustworthiness score is achieved when the data ratio is 1:1:2."
Appendices F.1 and F.2 select δk=8, δuk=2 and a 1:1:2 data ratio by maximizing 'average trustworthiness scores across in-domain and OOD datasets' on the same evaluation sets reported in Tables 1–2. The headline scores are thus the best point of a hyperparameter sweep over the reported metric, not independent predictions. The improvement of CA-DPO over baselines is partly forced by choosing the configuration that maximizes that exact strust measure on those exact datasets. Without a held-out model-selection set, the main quantitative claim over-reports the method's expected benefit; the numbers are optimized, not predicted.
full rationale
The paper's core training pipeline is not circular in the self-citation sense: it does not lean on prior work by the same authors to justify refusal boundaries, and the OOD evaluations on AOKVQA, GQA, MMMU, MMBench, BeyondVisQA, VizWiz, and VQAv2-IDK provide external measurements of refusal behavior that are independent of the training labels. Two loops, however, compromise the strength of the reported evidence. First, the Section 5.3 self-awareness analysis reuses the exact confidence estimator that generated the training labels and the CA-DPO loss, so the observed refusal-vs-confidence curve is the trained objective rather than an emergent discovery. Second, the main configuration (δk=8, δuk=2, ratio 1:1:2) was selected by maximizing the same trustworthiness metric on the same in-domain and OOD sets that later appear as the headline tables; the reported improvement is therefore a selected maximum rather than an unbiased estimate. Additionally, Table 2's Strust values are not reproducible from Eq. (5) (e.g., LLaVA1.5-7B: 2·12.00+46.10−100=−29.9, not −6.50), an internal inconsistency that further weakens the central quantitative claim. These are not self-citation or definitional circularities in the sense of importing an author's own theorem, but they are input-to-conclusion reductions in the evaluation loop.
Assumptions & free parameters
free parameters (4)
- Confidence thresholds δk and δuk =
Reported as δk=0.8, δuk=0.2 in Section 4.1 but as δk=8, δuk=2 in Appendix F.1; Figure 10 uses a 3-8 grid
- IDK-IT known-data ratio =
0.75 (about 25% IDK responses)
- CA-DPO data composition ratio (unknown:mixed:known) =
1:1:2
- Confidence estimation sampling configuration =
Unspecified
assumptions (5)
- domain assumption A model's confidence can be estimated by sampling multiple responses and computing accuracy against a hybrid evaluator.
- domain assumption All questions in the base VQA datasets are answerable from the provided visual information.
- domain assumption User preferences are captured by v(correct)=1, v(refusal)=0, v(incorrect)=-1, equivalently maximizing 2*Acc+RefR-1.
- domain assumption GPT-4o-generated unanswerable questions and the three-criteria filter correctly identify true extrinsic-boundary violations.
- domain assumption The hybrid evaluator (string matching plus Llama2-13B judgments) is a reliable proxy for human correctness judgment.
Cite this review
Pith. "Pith review of Drawing the Line: Enhancing Trustworthiness of MLLMs Through the Power of Refusal." pith.science (2026). https://pith.science/paper/FH2KGVYP
@misc{pith2026241211196,
author = {Pith},
title = {Pith review of: Drawing the Line: Enhancing Trustworthiness of MLLMs Through the Power of Refusal},
year = {2026},
howpublished = {\url{https://pith.science/paper/FH2KGVYP}},
note = {Machine review of arXiv:2412.11196}
}
read the original abstract
Multimodal large language models (MLLMs) excel at multimodal perception and understanding, yet their tendency to generate hallucinated or inaccurate responses undermines their trustworthiness. Existing methods have largely overlooked the importance of refusal responses as a means of enhancing MLLMs reliability. To bridge this gap, we present the Information Boundary-aware Learning Framework (InBoL), a novel approach that empowers MLLMs to refuse to answer user queries when encountering insufficient information. To the best of our knowledge, InBoL is the first framework that systematically defines the conditions under which refusal is appropriate for MLLMs using the concept of information boundaries proposed in our paper. This framework introduces a comprehensive data generation pipeline and tailored training strategies to improve the model's ability to deliver appropriate refusal responses. To evaluate the trustworthiness of MLLMs, we further propose a user-centric alignment goal along with corresponding metrics. Experimental results demonstrate a significant improvement in refusal accuracy without noticeably compromising the model's helpfulness, establishing InBoL as a pivotal advancement in building more trustworthy MLLMs.
Figures
Figures from the paper (9 more)
Reference graph
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