通过局部离散特征提升CNN可解释性,同时保持高性能。
Learning local discrete features in explainable-by-design convolutional neural networks
- 基于侧抑制机制设计可解释的CNN,用离散特征向量表示局部神经元交互。
- 在MNIST上仅用75万参数即达顶尖性能,且解释性更强。
- 适合关注模型决策过程的AI研发与安全应用者。
我们提出一种可解释性设计的卷积神经网络框架,旨在打破性能与可解释性的权衡。ExplaiNet模型包含高精度预测器(带残差或密集跳跃连接)和概率解释图,后者表达神经元的空间交互关系。图中每个节点值为局部离散特征(LDF)向量,即按激活强度排序的拮抗神经元索引,通过梯度下降学习。将LDF作为序列,复用分子生物学中的EXTREME方法挖掘序列基序,获得每层中间图像表示的离散特征基序矩阵。相比连续激活张量,该离散结构天然支持贝叶斯网络解释。通过观测收集与概率直接计算,可揭示相邻层级基序间的因果关系,并将模型输出归因于全局基序。在多个微型图像基准数据集上的实验表明,预测器在相同参数量或层数下表现与基线相当;本方法更有潜力超越基线。在已解决的MNIST分类任务中,使用标准训练设置和0.75百万参数,达到与当前最优单模型相当的性能。
原文摘要 · Abstract (English)
Our proposed framework attempts to break the trade-off between performance and explainability by introducing an explainable-by-design convolutional neural network (CNN) based on the lateral inhibition mechanism. The ExplaiNet model consists of the predictor, that is a high-accuracy CNN with residual or dense skip connections, and the explainer probabilistic graph that expresses the spatial interactions of the network neurons. The value on each graph node is a local discrete feature (LDF) vector, a patch descriptor that represents the indices of antagonistic neurons ordered by the strength of their activations, which are learned with gradient descent. Using LDFs as sequences we can increase the conciseness of explanations by repurposing EXTREME, an EM-based sequence motif discovery method that is typically used in molecular biology. Having a discrete feature motif matrix for each one of intermediate image representations, instead of a continuous activation tensor, allows us to leverage the inherent explainability of Bayesian networks. By collecting observations and directly calculating probabilities, we can explain causal relationships between motifs of adjacent levels and attribute the model's output to global motifs. Moreover, experiments on various tiny image benchmark datasets confirm that our predictor ensures the same level of performance as the baseline architecture for a given count of parameters and/or layers. Our novel method shows promise to exceed this performance while providing an additional stream of explanations. In the solved MNIST classification task, it reaches a comparable to the state-of-the-art performance for single models, using standard training setup and 0.75 million parameters.
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