25 research outputs found
Learning First-to-Spike Policies for Neuromorphic Control Using Policy Gradients
Artificial Neural Networks (ANNs) are currently being used as function
approximators in many state-of-the-art Reinforcement Learning (RL) algorithms.
Spiking Neural Networks (SNNs) have been shown to drastically reduce the energy
consumption of ANNs by encoding information in sparse temporal binary spike
streams, hence emulating the communication mechanism of biological neurons. Due
to their low energy consumption, SNNs are considered to be important candidates
as co-processors to be implemented in mobile devices. In this work, the use of
SNNs as stochastic policies is explored under an energy-efficient
first-to-spike action rule, whereby the action taken by the RL agent is
determined by the occurrence of the first spike among the output neurons. A
policy gradient-based algorithm is derived considering a Generalized Linear
Model (GLM) for spiking neurons. Experimental results demonstrate the
capability of online trained SNNs as stochastic policies to gracefully trade
energy consumption, as measured by the number of spikes, and control
performance. Significant gains are shown as compared to the standard approach
of converting an offline trained ANN into an SNN.Comment: Submitted for conference publicatio
CDNA-SNN: A New Spiking Neural Network for Pattern Classification using Neuronal Assemblies
Spiking neural networks (SNNs) mimic their biological counterparts more closely than their predecessors and are considered the third generation of artificial neural networks. It has been proven that networks of spiking neurons have a higher computational capacity and lower power requirements than sigmoidal neural networks. This paper introduces a new type of spiking neural network that draws inspiration and incorporates concepts from neuronal assemblies in the human brain. The proposed network, termed as CDNA-SNN, assigns each neuron learnable values known as Class-Dependent Neuronal Activations (CDNAs) which indicate the neuron’s average relative spiking activity in response to samples from different classes. A new learning algorithm that categorizes the neurons into different class assemblies based on their CDNAs is also presented. These neuronal assemblies are trained via a novel training method based on Spike-Timing Dependent Plasticity (STDP) to have high activity for their associated class and low firing rate for other classes. Also, using CDNAs, a new type of STDP that controls the amount of plasticity based on the assemblies of pre- and post-synaptic neurons is proposed. The performance of CDNA-SNN is evaluated on five datasets from the UCI machine learning repository, as well as MNIST and Fashion MNIST, using nested cross-validation for hyperparameter optimization. Our results show that CDNA-SNN significantly outperforms SWAT (p<0.0005) and SpikeProp (p<0.05) on 3/5 and SRESN (p<0.05) on 2/5 UCI datasets while using the significantly lower number of trainable parameters. Furthermore, compared to other supervised, fully connected SNNs, the proposed SNN reaches the best performance for Fashion MNIST and comparable performance for MNIST and N-MNIST, also utilizing much less (1-35%) parameters
Spiking-YOLO: Spiking Neural Network for Energy-Efficient Object Detection
Over the past decade, deep neural networks (DNNs) have demonstrated
remarkable performance in a variety of applications. As we try to solve more
advanced problems, increasing demands for computing and power resources has
become inevitable. Spiking neural networks (SNNs) have attracted widespread
interest as the third-generation of neural networks due to their event-driven
and low-powered nature. SNNs, however, are difficult to train, mainly owing to
their complex dynamics of neurons and non-differentiable spike operations.
Furthermore, their applications have been limited to relatively simple tasks
such as image classification. In this study, we investigate the performance
degradation of SNNs in a more challenging regression problem (i.e., object
detection). Through our in-depth analysis, we introduce two novel methods:
channel-wise normalization and signed neuron with imbalanced threshold, both of
which provide fast and accurate information transmission for deep SNNs.
Consequently, we present a first spiked-based object detection model, called
Spiking-YOLO. Our experiments show that Spiking-YOLO achieves remarkable
results that are comparable (up to 98%) to those of Tiny YOLO on non-trivial
datasets, PASCAL VOC and MS COCO. Furthermore, Spiking-YOLO on a neuromorphic
chip consumes approximately 280 times less energy than Tiny YOLO and converges
2.3 to 4 times faster than previous SNN conversion methods.Comment: Accepted to AAAI 202
SpikeGrad: An ANN-equivalent Computation Model for Implementing Backpropagation with Spikes
Event-based neuromorphic systems promise to reduce the energy consumption of
deep learning tasks by replacing expensive floating point operations on dense
matrices by low power sparse and asynchronous operations on spike events. While
these systems can be trained increasingly well using approximations of the
back-propagation algorithm, these implementations usually require high
precision errors for training and are therefore incompatible with the typical
communication infrastructure of neuromorphic circuits. In this work, we analyze
how the gradient can be discretized into spike events when training a spiking
neural network. To accelerate our simulation, we show that using a special
implementation of the integrate-and-fire neuron allows us to describe the
accumulated activations and errors of the spiking neural network in terms of an
equivalent artificial neural network, allowing us to largely speed up training
compared to an explicit simulation of all spike events. This way we are able to
demonstrate that even for deep networks, the gradients can be discretized
sufficiently well with spikes if the gradient is properly rescaled. This form
of spike-based backpropagation enables us to achieve equivalent or better
accuracies on the MNIST and CIFAR10 dataset than comparable state-of-the-art
spiking neural networks trained with full precision gradients. The algorithm,
which we call SpikeGrad, is based on accumulation and comparison operations and
can naturally exploit sparsity in the gradient computation, which makes it an
interesting choice for a spiking neuromorphic systems with on-chip learning
capacities