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arXiv 2603.03469cs.LGcond-mat.dis-nncond-mat.stat-mech
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扩散模型中的偏见泛化

Biased Generalization in Diffusion Models

Department of Computing Sciences, Bocconi University, Milan, Italy(计算科学系,博科尼大学,米兰,意大利)

Jerome Garnier-Brun, Luca Biggio, Davide Beltrame, Marc Mézard, Luca Saglietti

AI总结:

本文研究了扩散模型中偏见泛化的现象,揭示了模型在训练过程中持续降低测试损失的同时,倾向于生成与训练数据异常接近的样本,指出早期停止策略在隐私敏感应用中的局限性。

摘要:

生成模型中的泛化能力是指从有限数据集中学习底层分布并生成新样本的能力,其评估主要由留出性能和感知样本质量驱动。在实践中,训练通常在测试损失最小值处停止,被视为泛化能力的操作指标。我们通过识别训练过程中一个偏见泛化阶段来挑战这一观点,该阶段中模型继续降低测试损失,同时倾向于生成与训练数据异常接近的样本。通过在两个不相交的数据集上训练相同网络,并比较生成样本与训练数据的相互距离及其相似性,我们引入了一个偏见的量化度量,并在真实图像上展示了其存在。随后,我们研究了偏见的机制,使用一个受控的分层数据模型,其中可以精确获取分数和地面真实统计信息,从而精确表征其出现。我们将这一现象归因于深度网络中特征学习的序列性,其中粗结构以数据无关的方式在早期学习,而更细的特征则在后期以越来越依赖于个别训练样本的方式被解决。我们的结果表明,早期在测试损失最小值处停止,虽然在标准泛化标准下是最优的,但在隐私关键应用中可能不足。

英文摘要:

Generalization in generative modeling is defined as the ability to learn an underlying distribution from a finite dataset and produce novel samples, with evaluation largely driven by held-out performance and perceived sample quality. In practice, training is often stopped at the minimum of the test loss, taken as an operational indicator of generalization. We challenge this viewpoint by identifying a phase of biased generalization during training, in which the model continues to decrease the test loss while favoring samples with anomalously high proximity to training data. By training the same network on two disjoint datasets and comparing the mutual distances of generated samples and their similarity to training data, we introduce a quantitative measure of bias and demonstrate its presence on real images. We then study the mechanism of bias, using a controlled hierarchical data model where access to exact scores and ground-truth statistics allows us to precisely characterize its onset. We attribute this phenomenon to the sequential nature of feature learning in deep networks, where coarse structure is learned early in a data-independent manner, while finer features are resolved later in a way that increasingly depends on individual training samples. Our results show that early stopping at the test loss minimum, while optimal under standard generalization criteria, may be insufficient for privacy-critical applications.

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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