# Mental Simulation Collapse (MSC)

Interleaved multimodal reasoning inserts continuous visual latent blocks between text spans, but direct perturbation shows that dropping, replacing or shuffling these blocks barely changes the model's own answer probability, while the same perturbations to the textual reasoning trace hurt far more. The authors call this mental simulation collapse and introduce AnchorSim, which during training contrasts predictions with the visual pathway against predictions with it masked, forcing the latents to carry answer-relevant information. Built on Qwen2.5-VL-7B, AnchorSim-7B averages 62.4 across nine visual reasoning benchmarks, 13.5 points above the base model, and visual perturbations become consequential again.

Interleaved multimodal reasoning inserts continuous visual latent blocks between text spans, but direct perturbation shows that dropping, replacing or shuffling these blocks barely changes the model's own answer probability, while the same perturbations to the textual reasoning trace hurt far more. The authors call this mental simulation collapse and introduce AnchorSim, which during training contrasts predictions with the visual pathway against predictions with it masked, forcing the latents to carry answer-relevant information. Built on Qwen2.5-VL-7B, AnchorSim-7B averages 62.4 across nine visual reasoning benchmarks, 13.5 points above the base model, and visual perturbations become consequential again.