Overfitting of neural nets under class imbalance: Analysis and improvements for segmentation
File(s)MICCAI2019_Overfitting.pdf (1.97 MB)
Accepted version
Author(s)
Li, Z
Kamnitsas, K
Glocker, Benjamin
Type
Conference Paper
Abstract
Overfitting in deep learning has been the focus of a num-ber of recent works, yet its exact impact on the behaviour of neuralnetworks is not well understood. This study analyzes overfitting by ex-amining how the distribution of logits alters in relation to how muchthe model overfits. Specifically, we find that when training with few datasamples, the distribution of logit activations when processing unseen testsamples of an under-represented class tends to shift towards and evenacross the decision boundary, while the over-represented class seems un-affected. In image segmentation, foreground samples are often heavilyunder-represented. We observe that sensitivity of the model drops asa result of overfitting, while precision remains mostly stable. Based onour analysis, we derive asymmetric modifications of existing loss func-tions and regularizers including a large margin loss, focal loss, adver-sarial training and mixup, which specifically aim at reducing the shiftobserved when embedding unseen samples of the under-represented class.We study the case of binary segmentation of brain tumor core and showthat our proposed simple modifications lead to significantly improvedsegmentation performance over the symmetric variants.
Date Issued
2019-10-10
Date Acceptance
2019-06-05
Citation
Lecture Notes in Computer Science, 2019, pp.402-410
ISSN
0302-9743
Publisher
Springer Verlag
Start Page
402
End Page
410
Journal / Book Title
Lecture Notes in Computer Science
Copyright Statement
© Springer Nature Switzerland AG 2019.
Sponsor
Commission of the European Communities
Engineering & Physical Science Research Council (E
Identifier
https://link.springer.com/chapter/10.1007%2F978-3-030-32248-9_45
Grant Number
H2020 - 757173
EP/R511547/1
Source
International Conference on Medical Image Computing and Computer Assisted Intervention (MICCAI)
Subjects
Science & Technology
Technology
Life Sciences & Biomedicine
Computer Science, Artificial Intelligence
Computer Science, Software Engineering
Engineering, Biomedical
Neuroimaging
Imaging Science & Photographic Technology
Computer Science
Engineering
Neurosciences & Neurology
cs.LG
cs.LG
cs.CV
stat.ML
Artificial Intelligence & Image Processing
Publication Status
Published
Start Date
2019-10-13
Finish Date
2019-10-13
Coverage Spatial
Shenzhen, China
Date Publish Online
2019-10-10