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Knowledge Transfer via Distillation of Activation Boundaries Formed by Hidden Neurons (1811.03233v2)

Published 8 Nov 2018 in cs.LG, cs.CV, and stat.ML

Abstract: An activation boundary for a neuron refers to a separating hyperplane that determines whether the neuron is activated or deactivated. It has been long considered in neural networks that the activations of neurons, rather than their exact output values, play the most important role in forming classification friendly partitions of the hidden feature space. However, as far as we know, this aspect of neural networks has not been considered in the literature of knowledge transfer. In this paper, we propose a knowledge transfer method via distillation of activation boundaries formed by hidden neurons. For the distillation, we propose an activation transfer loss that has the minimum value when the boundaries generated by the student coincide with those by the teacher. Since the activation transfer loss is not differentiable, we design a piecewise differentiable loss approximating the activation transfer loss. By the proposed method, the student learns a separating boundary between activation region and deactivation region formed by each neuron in the teacher. Through the experiments in various aspects of knowledge transfer, it is verified that the proposed method outperforms the current state-of-the-art.

Citations (484)

Summary

  • The paper introduces an activation transfer loss that aligns activation boundaries between teacher and student networks to enhance classification performance.
  • It leverages a piecewise differentiable loss inspired by hinge loss, enabling efficient gradient-based optimization across varied neural architectures.
  • Experimental results demonstrate improvements in learning speed, data efficiency, and network compression, paving the way for robust transfer learning.

Analysis of Knowledge Transfer via Distillation of Activation Boundaries Formed by Hidden Neurons

The paper presents a novel approach to knowledge transfer in neural networks, focusing specifically on the distillation of activation boundaries formed by hidden neurons. This innovative method addresses a notable gap in current literature, which predominantly emphasizes the magnitude of neuron responses rather than their activation status.

Key Contributions

The primary contribution of this work is the introduction of an activation transfer loss specifically designed to minimize the disparity between the activation boundaries of teacher and student networks. The activation boundary, defined as the separating hyperplane that determines neuron activation, is a critical determinant in the formation of decision boundaries within neural networks. The proposed method underscores the significance of transferring these boundaries accurately to enhance classification performance in student models.

Given the non-differentiable nature of the original activation transfer loss, the authors propose a piecewise differentiable alternative loss function inspired by the hinge loss used in support vector machines. This alternative allows for gradient-based optimization, facilitating the practical implementation of the method in various neural architectures.

Experimental Results

The experiments validate the method across different dimensions of knowledge transfer:

  • Learning Efficiency: By enhancing the learning speed, the proposed method outstrips state-of-the-art alternatives, particularly as training epochs are reduced.
  • Data Efficiency: It exhibits superior generalization capabilities, especially when training data is scarce.
  • Network Compression: In scenarios requiring varying network sizes, the method shows robust performance, effectively handling both depth and channel reductions.
  • Transfer Learning: When applied to transfer learning tasks, such as using an ImageNet pre-trained ResNet50 to initialize a MobileNet on different targets, the method achieves results comparable to, or even surpassing, direct pre-training approaches.

Implications and Future Directions

From a theoretical standpoint, the results support the critical role of activation boundaries in neural networks’ decision-making capabilities. This insight could transform approaches to network understanding and development, prompting a shift from traditional magnitude-centric methods to those focusing on qualitative neuron states.

Practically, the proposed approach offers a promising path for improving student network efficiency without exhaustive resource needs. It provides a viable alternative to conventional pre-training methods, particularly for resource-constrained or time-sensitive applications.

The paper lays groundwork for future exploration of activation-boundary transfer in broader contexts, including but not limited to unsupervised or semi-supervised learning environments, and more complex network architectures beyond ReLU-based designs.

In conclusion, the distillation of activation boundaries put forth in this paper offers a compelling enhancement to knowledge transfer techniques. It opens new avenues for efficient model training and optimization, aligning with the growing demand for cost-effective yet powerful neural network solutions.