通过组合多个简单因果模型,提升对神经网络推理过程的准确抽象。
Combining Causal Models for More Accurate Abstractions of Neural Networks
- 用多个高阶因果模型组合建模网络不同输入下的计算状态。
- 在两个小任务上,新方法比单一模型更贴近GPT-2-small的实际行为。
- 可调节解释强度与忠实度平衡,适合追求高精度解释的研究者。
机制可解释性旨在通过揭示神经网络实现的高层算法来逆向工程模型。因果抽象提供了一个精确的标准:当网络的因果模型包含能实现算法因果模型中高层变量的低层特征时,即认为网络实现了该算法。实际应用中常面临的问题是,算法并非对网络的完全忠实抽象,仅部分捕捉模型的真实推理过程。本文提出一种解决方案:将多个简单高层模型进行组合,以生成更忠实的网络表征。通过学习该组合,可将神经网络建模为随输入变化的不同计算状态,实验表明该方法在两个小任务上对微调后的GPT-2-small更具准确性。我们观察到解释力(由高阶模型解释的输入数量衡量)与忠实度(交换干预准确率)之间的权衡。本方法允许在给定忠实度水平下,选择最优的模型组合,从而最准确地描述神经网络行为。
原文摘要 · Abstract (English)
Mechanistic interpretability aims to reverse engineer neural networks by uncovering which high-level algorithms they implement. Causal abstraction provides a precise notion of when a network implements an algorithm, i.e., a causal model of the network contains low-level features that realize the high-level variables in a causal model of the algorithm. A typical problem in practical settings is that the algorithm is not an entirely faithful abstraction of the network, meaning it only partially captures the true reasoning process of a model. We propose a solution where we combine different simple high-level models to produce a more faithful representation of the network. Through learning this combination, we can model neural networks as being in different computational states depending on the input provided, which we show is more accurate to GPT 2-small fine-tuned on two toy tasks. We observe a trade-off between the strength of an interpretability hypothesis, which we define in terms of the number of inputs explained by the high-level models, and its faithfulness, which we define as the interchange intervention accuracy. Our method allows us to modulate between the two, providing the most accurate combination of models that describe the behavior of a neural network given a faithfulness level.
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