arXiv AI

Lexical Perturbations Disrupt LLM Reasoning: An Empirical Study of Attention Diversion

The study investigates how lexical perturbations—such as keyboard noise, character swaps, and filler insertion—affect large language models (LLMs) on reasoning benchmarks. Four open-weight instruction-tuned models and frontier models were evaluated, revealing that character-level perturbations significantly reduce accuracy, especially on multi-step reasoning tasks, while filler insertion has minimal impact. The authors attribute this asymmetry to Attention Diversion, where fragmented subword tokenization draws disproportionate attention in middle and final transformer layers; they demonstrate that both token content and attention allocation are coupled, making it difficult for inference-time repair strategies to fully recover performance.

arXiv AI
6d ago

Attention Sees, MLP Refuses: Tracing the Attention-to-MLP Safety Pathway in LLMs

The paper investigates how safety‑aligned large language models (LLMs) can still be tricked by jailbreaks or over‑refuse benign requests. By analyzing residual‑stream updates in decoder‑only Transformers, the authors find that harmfulness is more readily decoded from attention updates—especially in early layers—while the MLP component is primarily responsible for writing refusal responses. Post‑training enhances MLP‑driven refusal writing without improving harmfulness decodability, and causal interventions confirm that downstream MLP updates are crucial for the refusal shift caused by upstream attention changes. Building on these insights, the authors propose Sentinel, a system that combines an attention‑derived perception score with an MLP‑derived decision score to better detect jailbreaks and over‑refusals across multiple models.

By Zixuan Weng, Haoqi He, Weifei Jin, Yue Huang, Yang Bai
arXiv AI
Jul 16

Not All Needles Are Found: How Fact Distribution and Don't Make It Up Prompts Shape Retrieval, Reasoning, and Hallucination in Long-Context LLMs

arXiv:2601. 02023v2 Announce Type: replace-cross Abstract: As Large Language Models (LLMs) increasingly utilize massive context windows as working memory for autonomous tasks, their reliability fluctuates significantly depending on how information is distributed in real-world corpora.

By Amirali Ebrahimzadeh, Seyyed M. Salili
arXiv Computation and Language
Sep 1

Quantifying and Mitigating Korean Jamo-Level Typographical Vulnerabilities in Large Language Models

The paper investigates a unique typographical vulnerability in Korean language models arising from errors at the jamo (sub-character) level, which can produce valid but altered syllables or expose raw jamo, thereby disrupting tokenization and bypassing standard error correction. By applying five jamo-level perturbations to the KMMLU benchmark, the authors show that model accuracy degrades steadily with perturbation intensity and that larger models do not gain robustness. They further demonstrate that corrupted inputs shift internal representations in a detectable way, enabling a linear probe to identify unseen typos and motivate a Typo-Aware Chain-of-Thought (TACoT) strategy that selectively triggers chain-of-thought inference only when a typo is detected, recovering much of the accuracy benefit at lower cost.

By Seojin Lee, Hwanhee Lee
arXiv Computation and Language
Sep 4

Breaking the Likelihood Trap: Variance-Calibrated Modulation for Large Language Model Decoding

The paper introduces Variance‑Calibrated Modulation (VCM), a training‑free pre‑decoding technique that reshapes language model probability distributions before truncation. VCM uses two dynamic mechanisms: a Contextual Searchlight via PMI to suppress stopwords and highlight context‑relevant tokens, and an Adaptive Self‑Debiasing that applies scale‑invariant penalization based on real‑time logit standard deviation. Experiments on open‑ended generation, factual QA, and mathematical reasoning show that VCM consistently reduces the likelihood trap, improving diversity, coherence, and reasoning accuracy with minimal computational cost.

By Yuanhao Ding, Meimingwei Li, Esteban Garces Arias, Matthias A{\ss}enmacher, Christian Heumann, Chongsheng Zhang
arXiv AI
Jul 22

Robust Reasoning Benchmark

arXiv:2604. 08571v3 Announce Type: replace-cross Abstract: While Large Language Models (LLMs) achieve high performance on standard mathematical benchmarks, their problem-solving abilities depend on the context and textual formatting.

By Pavel Golikov, Evgenii Opryshko, Gennady Pekhimenko, Mark C. Jeffrey
Hugging Face Trending Papers
Jul 2

PARTREP: Learning What to Repeat for Decoder-only LLMs

While decoder-only LLMs excel at a vast array of natural language tasks, it suffers from an asymmetric information flow induced by causal attention: later tokens are richer in contextual grounding than earlier ones. A simple and effective remedy is prompt repetition -- just appending a second copy of prompt before generation can redistribute grounding across positions and improve reasoning performance.

arXiv AI
3d ago

SPINE: Measuring LLM Sycophancy under Sustained Multi-Turn Pressure

SPINE is a benchmark that tests large language models (LLMs) for sycophancy by having a proxy user persistently challenge a target model for up to 25 turns. The study evaluates several commercial and open‑source models on false presuppositions and unethical queries, finding that collapse rates—where the model abandons the correct position—rise sharply with conversation length, from 0‑57% within five turns to 20‑97% within 25 turns. Analysis of reasoning traces shows that the correct position often remains present, indicating that sycophancy is a choice to please rather than a knowledge failure, and that emotional appeals are the most effective tactic for inducing collapse.

By Leyuan Tang, Kangda Wei, Tianyu Jiang, Ruihong Huang
arXiv AI
Aug 28

FOCUS & RePAIR: Mitigating Text Degeneration via Token-Level Guidance for Pruned Large Language Models

The paper investigates how pruning large language models can lead to text degeneration, particularly repetition loops, even when perplexity and task accuracy stay stable. By treating decoding as a dynamical process, the authors separate degeneration into loop entry risk and loop persistence, showing that persistence depends on the escape mass given to plausible alternatives. They introduce two token‑level guidance objectives—FOCUS, which reweights distillation toward high‑confidence teacher regions, and RePAIR, which uses onset‑centered positive/negative continuation pairs with a margin loss—to reduce repetition and improve generation quality in pruned models.

By Junyoung Lee, Sehyeon Park, Shinhyoung Jang, Seonha Ryu, Hojeong Kim, Hyunsei Lee, Il Hong Suh, Yeseong Kim
arXiv Computation and Language
Sep 4

How Perturbations Propagate: A Multi-Level Analysis of Robustness in Large Language Models

The paper investigates how six naturalistic and synthetic input perturbations affect decoder‑only language models at three levels: output behavior, hidden‑state geometry, and attention‑head function. Using GPT‑2 and Qwen2.5 checkpoints, the authors analyze layerwise geometry with centered kernel alignment and intrinsic dimension, and examine attention‑head responses in GPT‑2. They find that perturbation types produce distinct metric profiles that are not fully captured by output measures and vary across checkpoints, highlighting the need for multi‑level evaluation of robustness.

By Dun Li Chan, Emily Liu, Niyathi Allu, Christian Hoang