Entropy Is Not Enough: Unlocking Effective Reinforcement Learning for Visual Reasoning via Vision-Anchored Token Selection
Senjie Jin, Peixin Wang, Boyang Liu, Xiaoran Fan, Shuo Li, Zhiheng Xi, Jiazheng Zhang, Yuhao Zhou
Abstract
While token-level entropy is commonly recognized as effective for credit assignment in text-only reinforcement learning with verifiable rewards (RLVR), it remains unclear whether this mechanism still holds in visual reasoning. Our controlled study shows that this mechanism collapses in visual reasoning due to the omission of vision-sensitive tokens with naturally low entropy. Although existing multimodal RL methods increasingly acknowledge the importance of visual perception, they struggle to satisfy the inherent demand for interleaving precise perceptual grounding with semantic reasoning, either lacking systematic visual measurements or overlooking that token entropy primarily drives semantic exploration. To address this, we introduce VEPO (Vision-Entropy token-selection for Policy Optimization), an effective RL framework explicitly integrating visual sensitivity with token entropy via a principled multiplicative coupling, where VEPO redirects gradient credit toward tokens which are simultaneously visually grounded and highly informative. Extensive experiments demonstrate VEPO's leading performance, significantly outperforming the entropy-only baseline by 2.28 points at 7B-scale and 3.15 points at 3B-scale. Ablations further substantiate the soundness of our method.
AI Impact Assessments
(1 models)Scientific Impact Assessment: "Entropy Is Not Enough: Unlocking Effective Reinforcement Learning for Visual Reasoning via Vision-Anchored Token Selection"
1. Core Contribution
This paper identifies and diagnoses a specific failure mode: the entropy-based token selection mechanism that works well for text-only RLVR (reinforcement learning with verifiable rewards) collapses in visual reasoning tasks. The key insight is that vision-sensitive tokens naturally exhibit low entropy (because visual evidence disambiguates predictions), causing them to be systematically excluded by entropy-only selection. The proposed solution, VEPO, introduces a multiplicative coupling of visual sensitivity signals (Jensen-Shannon divergence and absolute entropy gap from counterfactual image perturbation) with token entropy, creating a joint scoring function that identifies "visual forking tokens"—tokens that are simultaneously visually grounded and informationally rich.
The problem formulation is clean: a counterfactual forward pass with a noise-perturbed image produces paired distributions, from which JSD captures distributional disagreement and |ΔH_t| captures uncertainty shift magnitude. These are combined via a noisy-OR-style aggregation and then modulated by entropy, selecting the top-k fraction for policy gradient updates.
2. Methodological Rigor
Strengths in experimental design:
Concerns:
3. Potential Impact
Direct applications: The method is immediately applicable to any VLM training pipeline using RLVR, particularly for visual math reasoning, diagram interpretation, and visual grounding tasks. The framework is modular—the token selection mechanism can be integrated into existing RL frameworks with minimal modification.
Broader influence: The paper contributes a conceptual insight that may influence how the community thinks about credit assignment in multimodal settings. The observation that different modalities contribute tokens with fundamentally different entropy characteristics could extend to audio-language, video-language, or other multimodal reasoning contexts. The counterfactual perturbation approach for measuring token-level visual dependency is a reusable measurement tool.
Limitations on impact: The method is specific to the training phase and requires an additional forward pass per batch, which may limit adoption in resource-constrained settings. The reliance on Gaussian noise as the perturbation method is somewhat ad hoc, and the paper acknowledges limited exploration of alternatives.
4. Timeliness & Relevance
This paper addresses a timely bottleneck. The community has been rapidly scaling RLVR from text-only to multimodal settings, with multiple concurrent works (VPPO, PAPO, NoisyRollout) tackling visual perception in RL. The "80/20 rule" for entropy-based token selection has become a widely referenced finding, and demonstrating its failure in the visual domain is a valuable corrective. The paper positions itself well within a very active research front (multiple 2025-2026 citations), making it highly relevant.
5. Strengths & Limitations
Key Strengths:
Notable Weaknesses:
Additional Observations
The qualitative cases (Figures 7-8) effectively illustrate the difference: VEPO selects content tokens tied to visual elements ("a", "c+b", "greater", "when") while entropy-only selects LaTeX formatting and discourse markers. This provides compelling evidence for the mechanism's face validity. The training dynamics comparison (Figure 5a-b) showing VEPO's stability versus competitors' premature convergence is also notable.
Generated Jun 3, 2026
Comparison History (21)
Paper 2 addresses a fundamental limitation in reinforcement learning for visual reasoning—a rapidly growing area at the intersection of multimodal AI and RL. Its principled insight that token entropy alone fails for vision-language models, and the proposed multiplicative coupling of visual sensitivity with entropy, offers a novel and broadly applicable contribution to the foundations of multimodal RL training. Paper 1, while practical and useful, is more of an engineering integration of existing LLM capabilities with established FEA software, offering incremental rather than foundational advances. Paper 2's impact spans broader ML/AI research communities.
Paper 2 likely has higher impact: it proposes a concrete, generalizable method (VEPO) addressing a timely bottleneck in multimodal RL for visual reasoning, with clear empirical gains and ablations suggesting methodological rigor. The approach can transfer across many vision-language RLVR settings and model scales, enabling real-world improvements in training multimodal agents. Paper 1 identifies an important evaluation failure mode and introduces a metric, but its primary impact is narrower (evaluation protocol design) and may be more quickly subsumed by evolving judge/benchmark practices.
Paper 1 explores a fundamental question regarding the capacity of LLMs for inductive scientific reasoning and hypothesis falsification. By bridging cognitive psychology (the Wason task) with LLM evaluation, it provides critical insights into the limitations of current AI agents in scientific discovery. While Paper 2 offers a strong technical algorithmic improvement for multimodal reinforcement learning, Paper 1 has broader interdisciplinary implications for AI, cognitive science, and the deployment of autonomous systems in real-world scientific research, giving it higher potential impact.
Paper 2 has higher potential impact because it provides a general theoretical foundation for a widely used family of methods (success conditioning / goal-conditioned RL / Decision Transformers), identifying the exact constrained optimization problem they solve and deriving interpretable identities with safety-relevant implications (conservative improvement, bounded distribution shift, observable failure modes). This breadth and timeliness (relevant to modern RL/LLM fine-tuning pipelines) make it broadly applicable across domains. Paper 1 is a solid, novel multimodal RL technique with empirical gains, but its impact is narrower and more contingent on a specific training setting.
Paper 2 likely has higher scientific impact due to broad, immediate applicability: reliability in tool-augmented LLM agent systems affects many domains (software, search, data analysis, automation). Its framing of orchestration as a budgeted runtime control problem with failure classification, targeted recovery, verification, and tracing is a broadly reusable systems contribution. The methodology includes controlled fault injection, multiple strong baselines, budget sweeps, and silent-failure analysis, supporting rigor and reproducibility. Paper 1 is novel and useful for multimodal RL, but its impact is narrower to RLVR/token-credit assignment research.
Paper 1 addresses a fundamental algorithmic challenge in multimodal reinforcement learning by identifying the limitations of entropy-based credit assignment in visual reasoning. Its novel VEPO framework offers a principled solution that advances the foundational capabilities of vision-language models, a highly active and impactful research area. While Paper 2 presents a valuable application of multi-agent LLMs for safety analysis, Paper 1's methodological contributions are likely to have a broader and more transformative impact across the rapidly growing field of multimodal AI and RL.
Paper 1 addresses a fundamental challenge in multimodal reinforcement learning by uncovering the failure of entropy-based credit assignment in visual reasoning and providing a principled solution (VEPO). This advances core training methodologies for vision-language models, a highly impactful field. Paper 2, while practically useful, offers a more application-focused agent framework for time-series data quality, which relies on assembling existing LLM capabilities rather than advancing fundamental model optimization paradigms.
Paper 2 likely has higher impact due to broader applicability and timeliness: programmatic LLM-on-KG reasoning addresses widely relevant issues (hallucination, scalability, compositional querying) across QA, information retrieval, databases, and agentic coding. The code-as-interface to KG schemas is a notable integration pattern that can generalize beyond QA tasks. It also reports a large empirical gain (up to 10.5%) on multiple established benchmarks. Paper 1 is innovative for multimodal RL credit assignment, but its impact may be narrower to RLVR/vision-language training regimes.
Paper 2 introduces a novel theoretical framework (Mean-Field Entropy Dynamics) to analyze LLM Multi-Agent Systems, addressing fundamental bottlenecks in orchestration. By uncovering the counterintuitive 'Reasoning Trap' and providing physically interpretable parameters for system stability, it offers broad architectural insights that could significantly influence the rapidly expanding field of autonomous agent design. While Paper 1 presents a strong, targeted algorithmic improvement for multimodal RL, Paper 2's theoretical and systems-level contributions suggest a broader and more foundational scientific impact.
Paper 1 likely has higher impact: it proposes a standards-like protocol filling a clear infrastructure gap (agent-to-instrument) with concrete primitives (capabilities, locking, safety gating, physically typed/uncertainty-aware measurements) that could be broadly adopted across autonomous labs, vendors, and domains. Its real-world applicability and cross-field breadth (automation, robotics, lab ops, metrology, safety, AI agents) are high and timely as autonomous science scales. Paper 2 is a solid algorithmic advance for multimodal RL, but appears more incremental and narrower in downstream adoption compared to a unifying protocol layer.
Paper 2 likely has higher scientific impact due to stronger novelty (identifying and fixing entropy-based credit assignment failure in visual RL), broader applicability across multimodal RL, vision-language models, and token-level optimization, and higher timeliness given rapid growth in VLM reasoning and RLVR. The proposed VEPO mechanism is conceptually general (coupling visual sensitivity with entropy) and could influence multiple training paradigms. Paper 1 is practically useful for relational ML/autocomplete, but is more incremental (masking, unified head, TF-IDF) and narrower in cross-field reach.
Paper 2 is likely to have higher scientific impact: it proposes a concrete, generalizable method (VEPO) addressing an active, timely bottleneck in multimodal RL (credit assignment for visual reasoning), with demonstrated gains at multi-billion-parameter scale and supporting ablations—suggesting strong real-world applicability in training vision-language agents. Paper 1 is novel and conceptually valuable for mechanistic understanding and cognitive-science links, but its impact may be narrower (synthetic task, smaller models) and more explanatory than enabling for broad downstream systems.
Paper 2 addresses a fundamental limitation in RLVR for visual reasoning—a rapidly growing area at the intersection of LLMs and multimodal AI. The insight that token-level entropy alone is insufficient for visual reasoning, and the principled multiplicative coupling of visual sensitivity with entropy, offers a broadly applicable contribution. It impacts the large community working on multimodal LLMs and RL-based training. Paper 1, while technically solid, addresses a more niche problem (skill library management for LLM agents) with narrower applicability. Paper 2's findings are more likely to influence future training paradigms for vision-language models.
Paper 1 presents a novel, methodologically rigorous technical advancement in the highly active field of multimodal reinforcement learning. By identifying a specific failure mode in existing RL methods and proposing a validated solution (VEPO) with strong empirical results, it is likely to directly influence future algorithmic development and generate significant citations in AI research. While Paper 2 offers a valuable conceptual framework for AI insurance and liability with high societal relevance, Paper 1's concrete technical contributions and experimental validation promise a deeper and more measurable scientific impact.
Paper 1 addresses a critical and universal vulnerability in the rapidly growing field of RLVR (verifiable rewards for reasoning models): reward hacking due to buggy verifiers. By introducing a fuzzing framework to identify these flaws before optimization, it provides a highly practical, broadly applicable solution to a fundamental alignment problem. While Paper 2 offers strong methodological improvements for multimodal RL, Paper 1's focus on the robustness and safety of reward signals has broader implications across all domains relying on RLVR, including math, coding, and tool use.
Paper 2 has higher estimated impact: it proposes a novel, generalizable RL method (VEPO) addressing a clear failure mode in multimodal RL (entropy-based credit assignment missing vision-sensitive low-entropy tokens), with demonstrated gains across model scales and supporting ablations—suggesting methodological rigor and broad applicability to vision-language reasoning and training pipelines. Paper 1 is valuable as a curriculum-grounded benchmark in graph theory, but its impact is narrower (evaluation-focused, domain-specific) and less likely to reshape methods across fields compared to a training framework that could affect many multimodal systems.
Paper 2 likely has higher impact: it targets a general RL mechanism failure in multimodal/visual reasoning, proposes a principled fix (vision-anchored token selection) and validates it across model scales with controlled studies and ablations. The contribution is broadly applicable to multimodal RL/LLMs and timely given rapid growth of vision-language RL. Paper 1 is innovative and clinically relevant, but its scope is narrower (lung cancer EHR trajectories) and real-world deployment faces domain/data/regulatory barriers, limiting near-term breadth despite strong application value.
Paper 2 addresses a critical bottleneck in healthcare AI by bridging structured EHR data and LLMs for interpretable clinical reasoning. Its potential real-world impact in clinical decision support and the broad applicability of multimodal alignment in medical informatics give it a higher overall scientific and societal impact compared to the specific algorithmic improvements in reinforcement learning for visual reasoning presented in Paper 1.
Paper 2 introduces a novel methodological contribution (VEPO) that addresses a fundamental gap in how reinforcement learning handles visual reasoning—specifically the failure of entropy-based credit assignment for vision-sensitive tokens. This has broad implications across multimodal AI, a rapidly growing field. Paper 1, while valuable as a benchmark for financial AI agents, is more domain-specific and incremental in nature (benchmark construction). Paper 2's principled multiplicative coupling mechanism is more likely to inspire follow-up research and influence training methodologies across diverse multimodal tasks.
Paper 1 introduces a more novel conceptual framework (Imaginative Perception Tokens) that addresses a fundamental limitation of VLMs—spatial reasoning about unobserved viewpoints—with a new paradigm of intermediate perceptual representations. It contributes new tasks, datasets (~20K examples), and reveals important insights about modality mismatch when forcing spatial reasoning through language. Paper 2 makes a solid but more incremental contribution by improving token-level credit assignment in multimodal RL. While both are rigorous, Paper 1's broader conceptual innovation (externalizing imagined perceptions) and its potential to reshape how spatial reasoning is approached in VLMs gives it higher long-term impact.