Title: Accelerated Predictive Coding Networks via Direct Kolen–Pollack Feedback Alignment
Primary area: probabilistic methods (Bayesian methods, variational inference, sampling, UQ, etc.)
Keywords: Predictive Coding, Artificial Intelligence, Local Learning, Backpropagation, Feedback Alignment, Neural Networks

Abstract: Backpropagation (BP) is the cornerstone algorithm for training artificial neural networks, yet its reliance on update-locked global error propagation limits biological plausibility and hardware efficiency. Predictive coding (PC), originally proposed as a model of the visual cortex, relies on local updates that allow parallel learning across layers. However, practical implementations face two key limitations: error signals must still propagate from the output to early layers through multiple inference-phase steps, and feedback decays exponentially during this process, leading to vanishing updates in early layers. These issues restrict the efficiency and scalability of PC, undermining its theoretical advantage in parallelization over BP. We propose direct Kolen–Pollack predictive coding (DKP-PC), which simultaneously addresses both feedback delay and exponential decay, yielding a more efficient and scalable variant of PC while preserving update locality. Leveraging the direct feedback alignment and direct Kolen–Pollack algorithms, DKP-PC introduces learnable feedback connections from the output layer to all hidden layers, establishing a direct pathway for error transmission. This yields an algorithm that reduces the theoretical error propagation time complexity from $\mathcal{O}(L)$, with $L$ being the network depth, to $\mathcal{O}(1)$, enabling parallel updates of the parameters. Moreover, empirical results demonstrate that DKP-PC achieves performance at least comparable to, and often exceeding, that of standard PC, while offering improved latency and computational performance. By enhancing both scalability and efficiency of PC, DKP-PC narrows the gap between biologically-plausible learning algorithms and BP, and unlocks the potential of local learning rules for hardware-efficient implementations.