Recognition: no theorem link
Do Vision Language Models Need to Process Image Tokens?
Pith reviewed 2026-05-10 18:20 UTC · model grok-4.3
The pith
Visual representations in VLMs converge to a stable low-complexity regime after early layers, unlike text, so deeper image-token processing adds little value for many tasks.
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
Core claim
Visual token representations in VLMs rapidly converge to a bounded-complexity regime in which entropy stabilizes, intrinsic dimensionality compresses, and trajectory curvature flattens to a near-constant profile, while textual representations continue substantial restructuring across depth. After stabilization, visual representations from different layers become largely interchangeable. Depth-wise truncation shows that single-token predictions remain robust to reduced visual depth, whereas multi-token generation requires sustained visual access; under deterministic decoding, truncation perturbs reasoning trajectories more than final outputs.
What carries the argument
Depth-wise measurement of representation complexity (entropy, intrinsic dimensionality, curvature) together with interchangeability tests and visual-depth truncation experiments.
If this is right
- Single-token predictions tolerate early truncation of visual depth with little loss.
- Multi-token generation requires continued access to visual representations across more layers.
- Truncation affects intermediate reasoning trajectories more than final outputs under deterministic decoding.
- Visual and textual streams evolve on different depth scales, so uniform deep multimodal stacks may be over-engineered for vision.
Where Pith is reading between the lines
- Architectures could process images only in early layers and reuse the stabilized features, lowering compute.
- The same convergence pattern may appear in other multimodal setups, allowing layer pruning or sharing.
- Task-specific visual depth could be chosen at inference time rather than fixed at training time.
Load-bearing premise
Stabilization of entropy, dimensionality, and curvature plus layer interchangeability directly means deeper visual layers contribute little additional functional value.
What would settle it
Measure accuracy and reasoning-path divergence on single-token and multi-token VLM tasks when visual processing is truncated exactly after the observed convergence point.
Figures
read the original abstract
Vision Language Models (VLMs) have achieved remarkable success by integrating visual encoders with large language models (LLMs). While VLMs process dense image tokens across deep transformer stacks (incurring substantial computational overhead), it remains fundamentally unclear whether sustained image-token processing is necessary for their performance or visual representations meaningfully evolve from early to later layers. In this work, we systematically investigate the functional role of image tokens in VLMs and show that visual representations rapidly converge to a bounded-complexity regime, \ie their entropy stabilizes, intrinsic dimensionality compresses, and trajectory curvature approaches a near-constant profile. In contrast, textual representations continue to undergo substantial restructuring across depth. Once stabilized, visual representations become largely interchangeable between layers, indicating limited additional transformation in deeper stages. Further, depth-wise visual truncation reveals that the necessity of visual processing is task-dependent, where single-token predictions remain comparatively robust to truncated visual depth, but multi-token generation require sustained access to visual representations. Under deterministic decoding, reducing visual depth perturbs intermediate reasoning trajectories more strongly than final outputs, suggesting that image tokens influence the structure of reasoning more than the ultimate conclusions. Collectively, these findings \textbf{question the assumption} that deeper visual processing is uniformly essential in VLMs, challenging the current paradigm of multimodal LLM architectures.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The paper investigates whether sustained processing of image tokens across deep layers is necessary in Vision Language Models. It reports that visual representations rapidly stabilize according to entropy, intrinsic dimensionality, and trajectory curvature metrics, in contrast to ongoing changes in textual representations; stabilized visual features are largely interchangeable across layers. Depth-wise truncation experiments indicate task-dependent effects, with single-token predictions remaining robust to reduced visual depth while multi-token generation suffers, and that truncation perturbs reasoning trajectories more than final outputs under deterministic decoding. The work concludes that deeper visual processing is not uniformly essential.
Significance. If substantiated, the results could support more efficient VLM designs by allowing shallower visual stacks for many tasks, reducing compute without proportional performance loss. The combination of descriptive representation metrics with direct functional truncation tests is a strength, as is the explicit comparison of visual versus textual dynamics and the attention to reasoning trajectories. These elements provide empirical grounding for questioning uniform deep multimodal fusion.
major comments (2)
- [§4] §4 (Experimental Setup and Truncation): the manuscript supplies no details on the specific VLMs tested, datasets used, number of runs, statistical controls, or the precise implementation of depth-wise visual truncation (e.g., token removal vs. masking, handling of positional encodings, or layer selection). This absence prevents verification of the reported stabilization thresholds and task-dependent performance differences.
- [§5] §5 (Results on Interchangeability): the claim that stabilized visual representations are 'largely interchangeable' between layers requires quantitative support (e.g., similarity scores or performance deltas when swapping layers); without reported effect sizes or controls for prompt length, it is unclear whether the interchangeability is functionally meaningful or merely statistical.
minor comments (2)
- [Abstract] Abstract: the notation 'i.e.' appears as LaTeX command 'ie' without proper rendering; minor typographical consistency issues appear in the description of curvature profiles.
- [§5] Figure captions (assumed in §5): ensure all plots include error bars or confidence intervals for the entropy and dimensionality curves to allow assessment of stabilization significance.
Simulated Author's Rebuttal
We thank the referee for their constructive and detailed feedback, which highlights important areas for improving the clarity and reproducibility of our work. We address each major comment below and will make the necessary revisions to the manuscript.
read point-by-point responses
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Referee: [§4] §4 (Experimental Setup and Truncation): the manuscript supplies no details on the specific VLMs tested, datasets used, number of runs, statistical controls, or the precise implementation of depth-wise visual truncation (e.g., token removal vs. masking, handling of positional encodings, or layer selection). This absence prevents verification of the reported stabilization thresholds and task-dependent performance differences.
Authors: We agree that §4 would benefit from substantially expanded implementation details to support verification and reproducibility. The original manuscript prioritized the core findings on representation dynamics and truncation effects but did not provide sufficient granularity on the experimental protocol. In the revised version, we will add a dedicated subsection in §4 that specifies the VLMs evaluated, the datasets and tasks employed, the number of runs performed along with statistical controls (means and standard deviations), and the exact mechanics of depth-wise truncation, including the choice between token removal and masking, preservation of positional encodings, and the criteria for layer selection based on the stabilization metrics introduced in §3. These additions will directly address the referee's concerns and enable independent verification of the stabilization thresholds and task-dependent results. revision: yes
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Referee: [§5] §5 (Results on Interchangeability): the claim that stabilized visual representations are 'largely interchangeable' between layers requires quantitative support (e.g., similarity scores or performance deltas when swapping layers); without reported effect sizes or controls for prompt length, it is unclear whether the interchangeability is functionally meaningful or merely statistical.
Authors: We acknowledge that the interchangeability claim in §5 would be strengthened by explicit quantitative metrics and controls. While the manuscript already demonstrates functional interchangeability through the truncation experiments (showing that performance remains largely intact when deeper visual layers are bypassed after stabilization), we did not include direct similarity measures or effect sizes. In the revision, we will augment §5 with cosine similarity scores between visual representations across layers, performance deltas from explicit layer-swapping experiments, and analyses that control for prompt length variations. These additions will quantify the degree of interchangeability and clarify that the observed stability is functionally meaningful rather than an artifact of statistical noise or prompt characteristics. revision: yes
Circularity Check
No significant circularity in empirical analysis
full rationale
The paper's central claims rest on direct empirical measurements of representation properties (entropy stabilization, intrinsic dimensionality compression, trajectory curvature) across layers and on controlled depth-wise truncation experiments that measure downstream task performance. These are observational and interventional results obtained from running the models, not derived quantities that reduce to the inputs by construction or via self-referential fitting. No equations, uniqueness theorems, or ansatzes are invoked that loop back to the paper's own definitions or prior self-citations in a load-bearing way. The work is therefore self-contained against external benchmarks and receives the default non-circularity finding.
Axiom & Free-Parameter Ledger
axioms (2)
- domain assumption Entropy, intrinsic dimensionality, and trajectory curvature are valid proxies for the functional complexity and necessity of visual representations.
- domain assumption Depth-wise truncation of visual tokens isolates the contribution of image processing without introducing confounding changes to the model's overall behavior.
Reference graph
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discussion (0)
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