588 research outputs found
Adversarial Training for Probabilistic Spiking Neural Networks
Classifiers trained using conventional empirical risk minimization or maximum
likelihood methods are known to suffer dramatic performance degradations when
tested over examples adversarially selected based on knowledge of the
classifier's decision rule. Due to the prominence of Artificial Neural Networks
(ANNs) as classifiers, their sensitivity to adversarial examples, as well as
robust training schemes, have been recently the subject of intense
investigation. In this paper, for the first time, the sensitivity of spiking
neural networks (SNNs), or third-generation neural networks, to adversarial
examples is studied. The study considers rate and time encoding, as well as
rate and first-to-spike decoding. Furthermore, a robust training mechanism is
proposed that is demonstrated to enhance the performance of SNNs under
white-box attacks.Comment: Submitted for possible publication. arXiv admin note: text overlap
with arXiv:1710.1070
Probabilistic spiking neural networks : Supervised, unsupervised and adversarial trainings
Spiking Neural Networks (SNNs), or third-generation neural networks, are networks of computation units, called neurons, in which each neuron with internal analogue dynamics receives as input and produces as output spiking, that is, binary sparse, signals. In contrast, second-generation neural networks, termed as Artificial Neural Networks (ANNs), rely on simple static non-linear neurons that are known to be energy-intensive, hindering their implementations on energy-limited processors such as mobile devices. The sparse event-based characteristics of SNNs for information transmission and encoding have made them more feasible for highly energy-efficient neuromorphic computing architectures. The most existing training algorithms for SNNs are based on deterministic spiking neurons that limit their flexibility and expressive power. Moreover, the SNNs are typically trained based on the back-propagation method, which unlike ANNs, it becomes challenging due to the non-differentiability nature of the spike dynamics. Considering these two key issues, this dissertation is devoted to develop probabilistic frameworks for SNNs that are tailored to the solution of supervised and unsupervised cognitive tasks. The SNNs utilize rich model, flexible and computationally tractable properties of Generalized Linear Model (GLM) neuron. The GLM is a probabilistic neural model that was previously considered within the computational neuroscience literature. A novel training method is proposed for the purpose of classification with a first-to-spike decoding rule, whereby the SNN can perform an early classification decision once spike firing is detected at an output neuron. This method is in contrast with conventional classification rules for SNNs that operate offline based on the number of output spikes at each output neuron. As a result, the proposed method improves the accuracy-inference complexity trade-off with respect to conventional decoding. For the first time in the field, the sensitivity of SNNs trained via Maximum Likelihood (ML) is studied under white-box adversarial attacks. Rate and time encoding, as well as rate and first-to-spike decoding, are considered. Furthermore, a robust training mechanism is proposed that is demonstrated to enhance the resilience of SNNs under adversarial examples. Finally, unsupervised training task for probabilistic SNNs is studied. Under generative model framework, multi-layers SNNs are designed for both encoding and generative parts. In order to train the Variational Autoencoders (VAEs), the standard ML approach is considered. To tackle the intractable inference part, variational learning approaches including doubly stochastic gradient learning, Maximum A Posterior (MAP)-based, and Rao-Blackwellization (RB)-based are considered. The latter is referred as the Hybrid Stochastic-MAP Variational Learning (HSM-VL) scheme. The numerical results show performance improvements using the HSM-VL method compared to the other two training schemes
Exploring Adversarial Attack in Spiking Neural Networks with Spike-Compatible Gradient
Recently, backpropagation through time inspired learning algorithms are
widely introduced into SNNs to improve the performance, which brings the
possibility to attack the models accurately given Spatio-temporal gradient
maps. We propose two approaches to address the challenges of gradient input
incompatibility and gradient vanishing. Specifically, we design a gradient to
spike converter to convert continuous gradients to ternary ones compatible with
spike inputs. Then, we design a gradient trigger to construct ternary gradients
that can randomly flip the spike inputs with a controllable turnover rate, when
meeting all zero gradients. Putting these methods together, we build an
adversarial attack methodology for SNNs trained by supervised algorithms.
Moreover, we analyze the influence of the training loss function and the firing
threshold of the penultimate layer, which indicates a "trap" region under the
cross-entropy loss that can be escaped by threshold tuning. Extensive
experiments are conducted to validate the effectiveness of our solution.
Besides the quantitative analysis of the influence factors, we evidence that
SNNs are more robust against adversarial attack than ANNs. This work can help
reveal what happens in SNN attack and might stimulate more research on the
security of SNN models and neuromorphic devices
Local learning algorithms for stochastic spiking neural networks
This dissertation focuses on the development of machine learning algorithms for spiking neural networks, with an emphasis on local three-factor learning rules that are in keeping with the constraints imposed by current neuromorphic hardware. Spiking neural networks (SNNs) are an alternative to artificial neural networks (ANNs) that follow a similar graphical structure but use a processing paradigm more closely modeled after the biological brain in an effort to harness its low power processing capability. SNNs use an event based processing scheme which leads to significant power savings when implemented in dedicated neuromorphic hardware such as Intel’s Loihi chip.
This work is distinguished by the consideration of stochastic SNNs based on spiking neurons that employ a stochastic spiking process, implementing generalized linear models (GLM) rather than deterministic thresholded spiking. In this framework, the spiking signals are random variables which may be sampled from a distribution defined by the neurons. The spiking signals may be observed or latent variables, with neurons whose outputs are observed termed visible neurons and otherwise termed hidden neurons. This choice provides a strong mathematical basis for maximum likelihood optimization of the network parameters via stochastic gradient descent, avoiding the issue of gradient backpropagation through the discontinuity created by the spiking process.
Three machine learning algorithms are developed for stochastic SNNs with a focus on power efficiency, learning efficiency and model adaptability; characteristics that are valuable in resource constrained settings. They are studied in the context of applications where low power learning on the edge is key. All of the learning rules that are derived include only local variables along with a global learning signal, making these algorithms tractable to implementation in current neuromorphic hardware.
First, a stochastic SNN that includes only visible neurons, the simplest case for probabilistic optimization, is considered. A policy gradient reinforcement learning (RL) algorithm is developed in which the stochastic SNN defines the policy, or state-action distribution, of an RL agent. Action choices are sampled directly from the policy by interpreting the outputs of the read-out neurons using a first to spike decision rule. This study highlights the power efficiency of the SNN in terms of spike frequency.
Next, an online meta-learning framework is proposed with the goal of progressively improving the learning efficiency of an SNN over a stream of tasks. In this setting, SNNs including both hidden and visible neurons are considered, posing a more complex maximum likelihood learning problem that is solved using a variational learning method. The meta-learning rule yields a hyperparameter initialization for SNN models that supports fast adaptation of the model to individualized data on edge devices.
Finally, moving away from the supervised learning paradigm, a hybrid adver-sarial training framework for SNNs, termed SpikeGAN, is developed. Rather than optimize for the likelihood of target spike patterns at the SNN outputs, the training is mediated by an auxiliary discriminator that provides a measure of how similar the spiking data is to a target distribution. Because no direct spiking patterns are given, the SNNs considered in adversarial learning include only hidden neurons. A Bayesian adaptation of the SpikeGAN learning rule is developed to broaden the range of temporal data that a single SpikeGAN can estimate. Additionally, the online meta-learning rule is extended to include meta-learning for SpikeGAN, to enable efficient generation of data from sequential data distributions
Spiking Generative Adversarial Networks With a Neural Network Discriminator: Local Training, Bayesian Models, and Continual Meta-Learning
Neuromorphic data carries information in spatio-temporal patterns encoded by
spikes. Accordingly, a central problem in neuromorphic computing is training
spiking neural networks (SNNs) to reproduce spatio-temporal spiking patterns in
response to given spiking stimuli. Most existing approaches model the
input-output behavior of an SNN in a deterministic fashion by assigning each
input to a specific desired output spiking sequence. In contrast, in order to
fully leverage the time-encoding capacity of spikes, this work proposes to
train SNNs so as to match distributions of spiking signals rather than
individual spiking signals. To this end, the paper introduces a novel hybrid
architecture comprising a conditional generator, implemented via an SNN, and a
discriminator, implemented by a conventional artificial neural network (ANN).
The role of the ANN is to provide feedback during training to the SNN within an
adversarial iterative learning strategy that follows the principle of
generative adversarial network (GANs). In order to better capture multi-modal
spatio-temporal distribution, the proposed approach -- termed SpikeGAN -- is
further extended to support Bayesian learning of the generator's weight.
Finally, settings with time-varying statistics are addressed by proposing an
online meta-learning variant of SpikeGAN. Experiments bring insights into the
merits of the proposed approach as compared to existing solutions based on
(static) belief networks and maximum likelihood (or empirical risk
minimization)
Exploiting Noise as a Resource for Computation and Learning in Spiking Neural Networks
Networks of spiking neurons underpin the extraordinary information-processing
capabilities of the brain and have emerged as pillar models in neuromorphic
intelligence. Despite extensive research on spiking neural networks (SNNs),
most are established on deterministic models. Integrating noise into SNNs leads
to biophysically more realistic neural dynamics and may benefit model
performance. This work presents the noisy spiking neural network (NSNN) and the
noise-driven learning rule (NDL) by introducing a spiking neuron model
incorporating noisy neuronal dynamics. Our approach shows how noise may act as
a resource for computation and learning and theoretically provides a framework
for general SNNs. Moreover, NDL provides an insightful biological rationale for
surrogate gradients. By incorporating various SNN architectures and algorithms,
we show that our approach exhibits competitive performance and improved
robustness against challenging perturbations than deterministic SNNs.
Additionally, we demonstrate the utility of the NSNN model for neural coding
studies. Overall, NSNN offers a powerful, flexible, and easy-to-use tool for
machine learning practitioners and computational neuroscience researchers.Comment: Fixed the bug in the BBL file generated with bibliography management
progra
Spiking neurons with short-term synaptic plasticity form superior generative networks
Spiking networks that perform probabilistic inference have been proposed both
as models of cortical computation and as candidates for solving problems in
machine learning. However, the evidence for spike-based computation being in
any way superior to non-spiking alternatives remains scarce. We propose that
short-term plasticity can provide spiking networks with distinct computational
advantages compared to their classical counterparts. In this work, we use
networks of leaky integrate-and-fire neurons that are trained to perform both
discriminative and generative tasks in their forward and backward information
processing paths, respectively. During training, the energy landscape
associated with their dynamics becomes highly diverse, with deep attractor
basins separated by high barriers. Classical algorithms solve this problem by
employing various tempering techniques, which are both computationally
demanding and require global state updates. We demonstrate how similar results
can be achieved in spiking networks endowed with local short-term synaptic
plasticity. Additionally, we discuss how these networks can even outperform
tempering-based approaches when the training data is imbalanced. We thereby
show how biologically inspired, local, spike-triggered synaptic dynamics based
simply on a limited pool of synaptic resources can allow spiking networks to
outperform their non-spiking relatives.Comment: corrected typo in abstrac
Spiking Denoising Diffusion Probabilistic Models
Spiking neural networks (SNNs) have ultra-low energy consumption and high
biological plausibility due to their binary and bio-driven nature compared with
artificial neural networks (ANNs). While previous research has primarily
focused on enhancing the performance of SNNs in classification tasks, the
generative potential of SNNs remains relatively unexplored. In our paper, we
put forward Spiking Denoising Diffusion Probabilistic Models (SDDPM), a new
class of SNN-based generative models that achieve high sample quality. To fully
exploit the energy efficiency of SNNs, we propose a purely Spiking U-Net
architecture, which achieves comparable performance to its ANN counterpart
using only 4 time steps, resulting in significantly reduced energy consumption.
Extensive experimental results reveal that our approach achieves
state-of-the-art on the generative tasks and substantially outperforms other
SNN-based generative models, achieving up to and
improvement on the CIFAR-10 and the CelebA datasets, respectively. Moreover, we
propose a threshold-guided strategy that can further improve the performances
by 16.7% in a training-free manner. The SDDPM symbolizes a significant
advancement in the field of SNN generation, injecting new perspectives and
potential avenues of exploration.Comment: Under Revie
- …