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Published in: Neuroinformatics 2/2019

20-08-2018 | Original Article

Characterizing Regularization Techniques for Spatial Filter Optimization in Oscillatory EEG Regression Problems

Guidelines Derived from Simulation and Real-World Data

Authors: Andreas Meinel, Sebastián Castaño-Candamil, Benjamin Blankertz, Fabien Lotte, Michael Tangermann

Published in: Neuroinformatics | Issue 2/2019

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Abstract

We report on novel supervised algorithms for single-trial brain state decoding. Their reliability and robustness are essential to efficiently perform neurotechnological applications in closed-loop. When brain activity is assessed by multichannel recordings, spatial filters computed by the source power comodulation (SPoC) algorithm allow identifying oscillatory subspaces. They regress to a known continuous trial-wise variable reflecting, e.g. stimulus characteristics, cognitive processing or behavior. In small dataset scenarios, this supervised method tends to overfit to its training data as the involved recordings via electroencephalogram (EEG), magnetoencephalogram or local field potentials generally provide a low signal-to-noise ratio. To improve upon this, we propose and characterize three types of regularization techniques for SPoC: approaches using Tikhonov regularization (which requires model selection via cross-validation), combinations of Tikhonov regularization and covariance matrix normalization as well as strategies exploiting analytical covariance matrix shrinkage. All proposed techniques were evaluated both in a novel simulation framework and on real-world data. Based on the simulation findings, we saw our expectations fulfilled, that SPoC regularization generally reveals the largest benefit for small training sets and under severe label noise conditions. Relevant for practitioners, we derived operating ranges of regularization hyperparameters for cross-validation based approaches and offer open source code. Evaluating all methods additionally on real-world data, we observed an improved regression performance mainly for datasets from subjects with initially poor performance. With this proof-of-concept paper, we provided a generalizable regularization framework for SPoC which may serve as a starting point for implementing advanced techniques in the future.

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Footnotes
1
To simplify the notation, epoched data X(t,e) will further on be written as a matrix X(e).
 
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Metadata
Title
Characterizing Regularization Techniques for Spatial Filter Optimization in Oscillatory EEG Regression Problems
Guidelines Derived from Simulation and Real-World Data
Authors
Andreas Meinel
Sebastián Castaño-Candamil
Benjamin Blankertz
Fabien Lotte
Michael Tangermann
Publication date
20-08-2018
Publisher
Springer US
Published in
Neuroinformatics / Issue 2/2019
Print ISSN: 1539-2791
Electronic ISSN: 1559-0089
DOI
https://doi.org/10.1007/s12021-018-9396-7

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