arXiv:2608.14712cs.CLcs.AI2026-08

Attention分析中忽略主锚点会颠倒结论,该研究提出用组分数据方法分离主锚与内容注意力。

Which Question Is Your Attention Metric Answering? Attention Rows as Compositional Data

论文配图:Which Question Is Your Attention Metric Answering? Attention Rows as Compositional Data
图 1 · 摘自论文原文
  • 将注意力行视为组分数据,用Aitchison距离分离主锚与内容注意力
  • 发现训练中熵下降主要来自主锚变强,而非注意力聚焦(1.4B模型中占79%)
  • 揭示现有比较方法因是否剔除主锚导致结论反转,适合关注注意力机制的读者

Transformer注意力矩阵的每一行都是对词元的概率分布,训练后大部分概率集中于单一‘主锚’词元(通常是首词)。标准注意力比较方法(余弦相似度、JS散度、香农熵)依赖一个极少报告的选择:保留主锚或剔除后重归一化。这一选择可导致结论反转——在五个模型家族的十个预训练模型中,17%至47%的头间相似性判断会因此改变;标准BERT头聚类中的显著结构实为该选择所致。根本原因在于单值统计量混淆了两个问题:主锚吸收多少注意力,以及其余注意力如何分配给内容词元。本研究通过组分数据分析框架,将注意力行分解为独立的主锚项和内容项:Aitchison距离正交分解,熵具精确分解恒等式,内容距离满足Transformer自身不变性。实际意义显著:多数观测到的熵衰减源于主锚增长(70M参数时占30%,1B时达95%,1.4B时为79%),错误通道剪枝可使困惑度提升百倍以上。研究明确了各约定的安全边界,验证了一个冻结的外样本预测器(一次确认、一次弃权、一次失败),并公开所有代码以复现结果。

原文摘要 · Abstract (English)

Each row of a transformer's attention matrix is a probability distribution over tokens, and in trained models most of that probability lands on a single \emph{sink} token, usually the first. Standard tools for comparing attention rows (cosine similarity, Jensen--Shannon divergence, Shannon entropy) therefore hinge on a choice papers rarely report: keep the sink, or drop it and renormalize. This choice can reverse conclusions. On ten pretrained models from five families, 17--47% of verdicts about which of two heads is more similar flip with the convention, and the most prominent structure in a standard BERT head-clustering pipeline is an artifact of it. The reason is that one-number summaries mix two questions: how much attention the sink takes, and how the rest is divided among the content tokens. Treating rows as compositional data separates them exactly: the Aitchison distance splits orthogonally into a sink term and a content term, entropy splits by an exact identity, and the content distance is characterized by invariances the transformer itself possesses. The separation matters in practice: most measured entropy collapse during training is the sink growing, not attention sharpening (30% of the drop at 70M parameters, 95% at 1B, 79% at 1.4B), and pruning heads with the wrong channel can inflate perplexity more than a hundredfold. We map where each convention is safe, test a frozen out-of-sample predictor (one confirmation, one abstention, one failure), and release code regenerating every number.

注意力分析组分数据变压器熵衰减

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