IIEU: Rethinking Neural Feature Activation from Decision-Making

Nonlinear Activation (Act) models which help fit the underlying mappings are critical for neural representation learning. Neuronal behaviors inspire basic Act functions, e.g., Softplus and ReLU. We instead seek improved explainable Act models by re-interpreting neural feature Act from a new philosophical perspective of Multi-Criteria Decision-Making (MCDM). By treating activation models as selective feature re-calibrators that suppress/emphasize features according to their importance scores measured by feature-filter similarities, we propose a set of specific properties of effective Act models with new intuitions. This helps us identify the unexcavated yet critical problem of mismatched feature scoring led by the differentiated norms of the features and filters. We present the Instantaneous Importance Estimation Units (IIEUs), a novel class of interpretable Act models that address the problem by re-calibrating the feature with the Instantaneous Importance (II) score (which we refer to as) estimated with the adaptive norm-decoupled feature-filter similarities, capable of modeling the cross-layer and -channel cues at a low cost. The extensive experiments on various vision benchmarks demonstrate the significant improvements of our IIEUs over the SOTA Act models and validate our interpretation of feature Act. By replacing the popular/SOTA Act models with IIEUs, the small ResNet-26s outperform/match the large ResNet-101s on ImageNet with far fewer parameters and computations.