63 research outputs found
Active Class Incremental Learning for Imbalanced Datasets
Incremental Learning (IL) allows AI systems to adapt to streamed data. Most
existing algorithms make two strong hypotheses which reduce the realism of the
incremental scenario: (1) new data are assumed to be readily annotated when
streamed and (2) tests are run with balanced datasets while most real-life
datasets are actually imbalanced. These hypotheses are discarded and the
resulting challenges are tackled with a combination of active and imbalanced
learning. We introduce sample acquisition functions which tackle imbalance and
are compatible with IL constraints. We also consider IL as an imbalanced
learning problem instead of the established usage of knowledge distillation
against catastrophic forgetting. Here, imbalance effects are reduced during
inference through class prediction scaling. Evaluation is done with four visual
datasets and compares existing and proposed sample acquisition functions.
Results indicate that the proposed contributions have a positive effect and
reduce the gap between active and standard IL performance.Comment: Accepted in IPCV workshop from ECCV202
Learning latent representations across multiple data domains using Lifelong VAEGAN
The problem of catastrophic forgetting occurs in deep learning models trained on multiple databases in a sequential manner. Recently, generative replay mechanisms (GRM), have been proposed to reproduce previously learned knowledge aiming to reduce the forgetting. However, such approaches lack an appropriate inference model and therefore can not provide latent representations of data. In this paper, we propose a novel lifelong learning approach, namely the Lifelong VAEGAN (L-VAEGAN), which not only induces a powerful generative replay network but also learns meaningful latent representations, benefiting representation learning. L-VAEGAN can allow to automatically embed the information associated with different domains into several clusters in the latent space, while also capturing semantically meaningful shared latent variables, across different data domains. The proposed model supports many downstream tasks that traditional generative replay methods can not, including interpolation and inference across different data domains
Contrast Adaptive Tissue Classification by Alternating Segmentation and Synthesis
Deep learning approaches to the segmentation of magnetic resonance images
have shown significant promise in automating the quantitative analysis of brain
images. However, a continuing challenge has been its sensitivity to the
variability of acquisition protocols. Attempting to segment images that have
different contrast properties from those within the training data generally
leads to significantly reduced performance. Furthermore, heterogeneous data
sets cannot be easily evaluated because the quantitative variation due to
acquisition differences often dwarfs the variation due to the biological
differences that one seeks to measure. In this work, we describe an approach
using alternating segmentation and synthesis steps that adapts the contrast
properties of the training data to the input image. This allows input images
that do not resemble the training data to be more consistently segmented. A
notable advantage of this approach is that only a single example of the
acquisition protocol is required to adapt to its contrast properties. We
demonstrate the efficacy of our approaching using brain images from a set of
human subjects scanned with two different T1-weighted volumetric protocols.Comment: 10 pages. MICCAI SASHIMI Workshop 202
Online Continual Learning on Sequences
Online continual learning (OCL) refers to the ability of a system to learn
over time from a continuous stream of data without having to revisit previously
encountered training samples. Learning continually in a single data pass is
crucial for agents and robots operating in changing environments and required
to acquire, fine-tune, and transfer increasingly complex representations from
non-i.i.d. input distributions. Machine learning models that address OCL must
alleviate \textit{catastrophic forgetting} in which hidden representations are
disrupted or completely overwritten when learning from streams of novel input.
In this chapter, we summarize and discuss recent deep learning models that
address OCL on sequential input through the use (and combination) of synaptic
regularization, structural plasticity, and experience replay. Different
implementations of replay have been proposed that alleviate catastrophic
forgetting in connectionists architectures via the re-occurrence of (latent
representations of) input sequences and that functionally resemble mechanisms
of hippocampal replay in the mammalian brain. Empirical evidence shows that
architectures endowed with experience replay typically outperform architectures
without in (online) incremental learning tasks.Comment: L. Oneto et al. (eds.), Recent Trends in Learning From Data, Studies
in Computational Intelligence 89
Increasing generality in machine learning through procedural content generation
Procedural Content Generation (PCG) refers to the practice, in videogames and
other games, of generating content such as levels, quests, or characters
algorithmically. Motivated by the need to make games replayable, as well as to
reduce authoring burden, limit storage space requirements, and enable
particular aesthetics, a large number of PCG methods have been devised by game
developers. Additionally, researchers have explored adapting methods from
machine learning, optimization, and constraint solving to PCG problems. Games
have been widely used in AI research since the inception of the field, and in
recent years have been used to develop and benchmark new machine learning
algorithms. Through this practice, it has become more apparent that these
algorithms are susceptible to overfitting. Often, an algorithm will not learn a
general policy, but instead a policy that will only work for a particular
version of a particular task with particular initial parameters. In response,
researchers have begun exploring randomization of problem parameters to
counteract such overfitting and to allow trained policies to more easily
transfer from one environment to another, such as from a simulated robot to a
robot in the real world. Here we review the large amount of existing work on
PCG, which we believe has an important role to play in increasing the
generality of machine learning methods. The main goal here is to present RL/AI
with new tools from the PCG toolbox, and its secondary goal is to explain to
game developers and researchers a way in which their work is relevant to AI
research
Mutation Bias Favors Protein Folding Stability in the Evolution of Small Populations
Mutation bias in prokaryotes varies from extreme adenine and thymine (AT) in obligatory endosymbiotic or parasitic bacteria to extreme guanine and cytosine (GC), for instance in actinobacteria. GC mutation bias deeply influences the folding stability of proteins, making proteins on the average less hydrophobic and therefore less stable with respect to unfolding but also less susceptible to misfolding and aggregation. We study a model where proteins evolve subject to selection for folding stability under given mutation bias, population size, and neutrality. We find a non-neutral regime where, for any given population size, there is an optimal mutation bias that maximizes fitness. Interestingly, this optimal GC usage is small for small populations, large for intermediate populations and around 50% for large populations. This result is robust with respect to the definition of the fitness function and to the protein structures studied. Our model suggests that small populations evolving with small GC usage eventually accumulate a significant selective advantage over populations evolving without this bias. This provides a possible explanation to the observation that most species adopting obligatory intracellular lifestyles with a consequent reduction of effective population size shifted their mutation spectrum towards AT. The model also predicts that large GC usage is optimal for intermediate population size. To test these predictions we estimated the effective population sizes of bacterial species using the optimal codon usage coefficients computed by dos Reis et al. and the synonymous to non-synonymous substitution ratio computed by Daubin and Moran. We found that the population sizes estimated in these ways are significantly smaller for species with small and large GC usage compared to species with no bias, which supports our prediction
Evaluation of appendicitis risk prediction models in adults with suspected appendicitis
Background
Appendicitis is the most common general surgical emergency worldwide, but its diagnosis remains challenging. The aim of this study was to determine whether existing risk prediction models can reliably identify patients presenting to hospital in the UK with acute right iliac fossa (RIF) pain who are at low risk of appendicitis.
Methods
A systematic search was completed to identify all existing appendicitis risk prediction models. Models were validated using UK data from an international prospective cohort study that captured consecutive patients aged 16–45 years presenting to hospital with acute RIF in March to June 2017. The main outcome was best achievable model specificity (proportion of patients who did not have appendicitis correctly classified as low risk) whilst maintaining a failure rate below 5 per cent (proportion of patients identified as low risk who actually had appendicitis).
Results
Some 5345 patients across 154 UK hospitals were identified, of which two‐thirds (3613 of 5345, 67·6 per cent) were women. Women were more than twice as likely to undergo surgery with removal of a histologically normal appendix (272 of 964, 28·2 per cent) than men (120 of 993, 12·1 per cent) (relative risk 2·33, 95 per cent c.i. 1·92 to 2·84; P < 0·001). Of 15 validated risk prediction models, the Adult Appendicitis Score performed best (cut‐off score 8 or less, specificity 63·1 per cent, failure rate 3·7 per cent). The Appendicitis Inflammatory Response Score performed best for men (cut‐off score 2 or less, specificity 24·7 per cent, failure rate 2·4 per cent).
Conclusion
Women in the UK had a disproportionate risk of admission without surgical intervention and had high rates of normal appendicectomy. Risk prediction models to support shared decision‐making by identifying adults in the UK at low risk of appendicitis were identified
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