6,321 research outputs found
Gradient-free activation maximization for identifying effective stimuli
A fundamental question for understanding brain function is what types of
stimuli drive neurons to fire. In visual neuroscience, this question has also
been posted as characterizing the receptive field of a neuron. The search for
effective stimuli has traditionally been based on a combination of insights
from previous studies, intuition, and luck. Recently, the same question has
emerged in the study of units in convolutional neural networks (ConvNets), and
together with this question a family of solutions were developed that are
generally referred to as "feature visualization by activation maximization."
We sought to bring in tools and techniques developed for studying ConvNets to
the study of biological neural networks. However, one key difference that
impedes direct translation of tools is that gradients can be obtained from
ConvNets using backpropagation, but such gradients are not available from the
brain. To circumvent this problem, we developed a method for gradient-free
activation maximization by combining a generative neural network with a genetic
algorithm. We termed this method XDream (EXtending DeepDream with real-time
evolution for activation maximization), and we have shown that this method can
reliably create strong stimuli for neurons in the macaque visual cortex (Ponce
et al., 2019). In this paper, we describe extensive experiments characterizing
the XDream method by using ConvNet units as in silico models of neurons. We
show that XDream is applicable across network layers, architectures, and
training sets; examine design choices in the algorithm; and provide practical
guides for choosing hyperparameters in the algorithm. XDream is an efficient
algorithm for uncovering neuronal tuning preferences in black-box networks
using a vast and diverse stimulus space.Comment: 16 pages, 8 figures, 3 table
Better Safe Than Sorry: An Adversarial Approach to Improve Social Bot Detection
The arm race between spambots and spambot-detectors is made of several cycles
(or generations): a new wave of spambots is created (and new spam is spread),
new spambot filters are derived and old spambots mutate (or evolve) to new
species. Recently, with the diffusion of the adversarial learning approach, a
new practice is emerging: to manipulate on purpose target samples in order to
make stronger detection models. Here, we manipulate generations of Twitter
social bots, to obtain - and study - their possible future evolutions, with the
aim of eventually deriving more effective detection techniques. In detail, we
propose and experiment with a novel genetic algorithm for the synthesis of
online accounts. The algorithm allows to create synthetic evolved versions of
current state-of-the-art social bots. Results demonstrate that synthetic bots
really escape current detection techniques. However, they give all the needed
elements to improve such techniques, making possible a proactive approach for
the design of social bot detection systems.Comment: This is the pre-final version of a paper accepted @ 11th ACM
Conference on Web Science, June 30-July 3, 2019, Boston, U
SINVAD: Search-based Image Space Navigation for DNN Image Classifier Test Input Generation
The testing of Deep Neural Networks (DNNs) has become increasingly important
as DNNs are widely adopted by safety critical systems. While many test adequacy
criteria have been suggested, automated test input generation for many types of
DNNs remains a challenge because the raw input space is too large to randomly
sample or to navigate and search for plausible inputs. Consequently, current
testing techniques for DNNs depend on small local perturbations to existing
inputs, based on the metamorphic testing principle. We propose new ways to
search not over the entire image space, but rather over a plausible input space
that resembles the true training distribution. This space is constructed using
Variational Autoencoders (VAEs), and navigated through their latent vector
space. We show that this space helps efficiently produce test inputs that can
reveal information about the robustness of DNNs when dealing with realistic
tests, opening the field to meaningful exploration through the space of highly
structured images
Tile Pattern KL-Divergence for Analysing and Evolving Game Levels
This paper provides a detailed investigation of using the Kullback-Leibler
(KL) Divergence as a way to compare and analyse game-levels, and hence to use
the measure as the objective function of an evolutionary algorithm to evolve
new levels. We describe the benefits of its asymmetry for level analysis and
demonstrate how (not surprisingly) the quality of the results depends on the
features used. Here we use tile-patterns of various sizes as features.
When using the measure for evolution-based level generation, we demonstrate
that the choice of variation operator is critical in order to provide an
efficient search process, and introduce a novel convolutional mutation operator
to facilitate this. We compare the results with alternative generators,
including evolving in the latent space of generative adversarial networks, and
Wave Function Collapse. The results clearly show the proposed method to provide
competitive performance, providing reasonable quality results with very fast
training and reasonably fast generation.Comment: 8 pages plus references. Proceedings of GECCO 201
Tools for Landscape Analysis of Optimisation Problems in Procedural Content Generation for Games
The term Procedural Content Generation (PCG) refers to the (semi-)automatic
generation of game content by algorithmic means, and its methods are becoming
increasingly popular in game-oriented research and industry. A special class of
these methods, which is commonly known as search-based PCG, treats the given
task as an optimisation problem. Such problems are predominantly tackled by
evolutionary algorithms.
We will demonstrate in this paper that obtaining more information about the
defined optimisation problem can substantially improve our understanding of how
to approach the generation of content. To do so, we present and discuss three
efficient analysis tools, namely diagonal walks, the estimation of high-level
properties, as well as problem similarity measures. We discuss the purpose of
each of the considered methods in the context of PCG and provide guidelines for
the interpretation of the results received. This way we aim to provide methods
for the comparison of PCG approaches and eventually, increase the quality and
practicality of generated content in industry.Comment: 30 pages, 8 figures, accepted for publication in Applied Soft
Computin
- …