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Random feedback weights support learning in deep neural networks (1411.0247v1)

Published 2 Nov 2014 in q-bio.NC and cs.NE

Abstract: The brain processes information through many layers of neurons. This deep architecture is representationally powerful, but it complicates learning by making it hard to identify the responsible neurons when a mistake is made. In machine learning, the backpropagation algorithm assigns blame to a neuron by computing exactly how it contributed to an error. To do this, it multiplies error signals by matrices consisting of all the synaptic weights on the neuron's axon and farther downstream. This operation requires a precisely choreographed transport of synaptic weight information, which is thought to be impossible in the brain. Here we present a surprisingly simple algorithm for deep learning, which assigns blame by multiplying error signals by random synaptic weights. We show that a network can learn to extract useful information from signals sent through these random feedback connections. In essence, the network learns to learn. We demonstrate that this new mechanism performs as quickly and accurately as backpropagation on a variety of problems and describe the principles which underlie its function. Our demonstration provides a plausible basis for how a neuron can be adapted using error signals generated at distal locations in the brain, and thus dispels long-held assumptions about the algorithmic constraints on learning in neural circuits.

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Authors (4)
  1. Timothy P. Lillicrap (19 papers)
  2. Daniel Cownden (1 paper)
  3. Douglas B. Tweed (1 paper)
  4. Colin J. Akerman (1 paper)
Citations (167)

Summary

  • The paper demonstrates that random feedback weights can effectively guide the learning process in deep neural networks without precise synaptic alignment.
  • The authors use a feedback alignment mechanism that replaces backpropagation while maintaining comparable learning accuracy on benchmark tasks.
  • This approach offers a promising framework for developing biologically plausible, efficient deep learning models that simplify error signal transmission.

Analysis of Efficient Learning with Random Feedback Weights in Deep Neural Networks

The paper "Random feedback weights support learning in deep neural networks" introduces a novel approach to learning within deep neural networks using random feedback weights. The authors propose a mechanism by which neurons can be adapted using error signals transferred through random synaptic weights, challenging traditional concepts in neural learning algorithms.

Key Methodology and Findings

The research posits an alternative to the conventional backpropagation of error, which has been shown to be biologically implausible due to the requirement of precise synaptic weight transport. Instead, the proposed method employs a feedback mechanism using random matrices, referred to as feedback alignment. This mechanism maintains the efficiency and accuracy comparable to backpropagation across a range of tasks while avoiding the logistical complexities associated with weight transport.

The paper demonstrates that utilizing random feedback weights can effectively transmit teaching signals throughout neural networks. To substantiate their claims, the authors provide empirical evidence showing that feedback alignment achieves equivalent learning rates as backpropagation in several benchmark tasks, including the classification of handwritten digits and function approximation. Interestingly, their findings indicate that despite the random nature of the feedback weights, adjustments in the network's forward synaptic weights enable the feedback matrix to provide effective teaching signals, aligning the update directions with those prescribed by backpropagation.

Theoretical Implications

The introduction of random feedback weights in learning algorithms carries notable implications for artificial intelligence and theoretical neuroscience. From a computational standpoint, the simplification of learning mechanisms by omitting the necessity for precise feedback alignment provides a promising avenue for creating more efficient and adaptable learning models. This approach also suggests new paradigms for biologically plausible learning, where reciprocal random feedback can facilitate effective information transfer between neural layers without necessitating detailed synaptic communication.

Practical Impact and Future Directions

This feedback alignment strategy can lead to developments in designing biologically inspired neural networks that mimic brain processes more closely than traditional methods. It opens potential pathways for bridging neuroscientific insights with advanced AI architectures, providing a framework for integrating neural learning principles with deep learning applications.

Moving forward, it will be essential to explore the scalability and versatility of feedback alignment in increasingly complex and dynamic environments. This could involve assessing its efficacy within reinforcement learning paradigms and identifying potential real-world applications where random feedback mechanisms could enhance system robustness and adaptability.

Conclusion

The paper challenges longstanding assumptions about the constraints on learning in neural networks and posits a simpler yet effective alternative through random feedback alignment. By demonstrating that random weights can support the learning process, the authors contribute to a broader understanding of how deep neural networks can be optimized for both biological plausibility and practical application, fostering advances in AI that leverage the powerful representational capacity inherent in deep architectures.