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arXiv 2601.04098cs.CLcs.AI
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分层位置偏倚在短上下文语言建模中的表现

Layer-wise Positional Bias in Short-Context Language Modeling

Tehran Institute for Advanced Studies, Khatam University, Iran(德黑兰高级研究院,卡坦大学,伊朗);School of Electrical and Computer Engineering, University of Tehran, Iran(德黑兰理工大学电气与计算机工程学院,伊朗)

Maryam Rahimi, Mahdi Nouri, Yadollah Yaghoobzadeh

AI总结:

本研究提出一种基于归因的框架,分析短上下文语言建模中各层的位置偏倚,发现深度增加时近期偏倚增强,首次偏倚减弱,且早期层更倾向内容词。

摘要:

语言模型常常表现出对输入中特定位置信息的偏好,无论语义相关性如何。尽管位置偏倚已在各种上下文中被研究,从注意力sink到长上下文设置中的任务性能退化,但先前的工作尚未建立这些偏倚如何在单个层和输入位置上演变,或如何独立于任务复杂性变化。我们引入了一个基于归因的框架来分析短上下文语言建模中的位置效应。使用层传导与滑动窗口方法,我们量化了每一层如何在输入位置上分配重要性,从而得到分层位置重要性轮廓。我们发现这些轮廓是架构特定的,在输入上保持稳定,并且对词汇 scrambling 不变。通过刻画这些轮廓,我们发现存在显著的近期偏倚,随着深度增加而增强,以及微妙的首次偏倚,随着模型深度增加而减弱。除了位置结构外,我们还显示早期层在所有位置上更倾向于加权内容词而非功能词,而后期层则失去这种词型区分。

英文摘要:

Transformer language models systematically prefer tokens at specific input positions regardless of semantic relevance---a phenomenon known as positional bias. Prior work characterizes this bias in model behavior through performance drops in long-context tasks or in model architecture through attention-based analyses. However, it remains unmeasured how input positions actually drive predictions layer by layer. We introduce a layer conductance framework within a sliding-window design, applied to short-context next-word prediction to isolate model-internal behavior from task and context-window pressure. The resulting layer-wise positional importance profiles are stable across diverse texts and lexical scrambling, confirming they reflect model-internal structure. Characterizing how these profiles evolve across depth, we find recency bias increases monotonically while primacy bias is subtle and diminishes. We also find that this positional bias is not uniform across word types: function words exhibit higher recency bias while content words show higher primacy bias.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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