Design and Analysis of Temporal Representations in Neural Networks

원문 초록

Neural networks, spiking or not, compute with amplitudes: activation values, spike counts, firing rates, never event times. No measure exists of how much a network uses time. We propose one, the degree of temporal representation: the fraction of a network's four functions (encoding, activation, decoding, learning) whose variables or parameters are temporal, and hypothesise that it predicts performance on temporal tasks. At fixed architecture, accuracy and energy efficiency increase with the degree: a delay network of maximal degree reaches 98.94\% on Google Speech Commands with 175k parameters, above transformers. To test whether networks of different degree really differ, we convert the delay network into artificial and spiking networks with the same inputs and outputs. From this common start, the artificial one learns differently and temporal gradients depend on event times. Hence we obtain a design rule: for temporal data, make event times variables of a network's functions. Spiking networks, converted after training, keep the delay network's accuracy, unreachable by spiking networks trained from scratch.