High-pass filtering artifacts in multivariate classification of neural time series data

Joram van Driel, Christian N.L. Olivers, Johannes J. Fahrenfort*

*Corresponding author for this work

Research output: Contribution to JournalArticleAcademicpeer-review


Background: Traditionally, EEG/MEG data are high-pass filtered and baseline-corrected to remove slow drifts. Minor deleterious effects of high-pass filtering in traditional time-series analysis have been well-documented, including temporal displacements. However, its effects on time-resolved multivariate pattern classification analyses (MVPA) are largely unknown. New method: To prevent potential displacement effects, we extend an alternative method of removing slow drift noise – robust detrending – with a procedure in which we mask out all cortical events from each trial. We refer to this method as trial-masked robust detrending. Results: In both real and simulated EEG data of a working memory experiment, we show that both high-pass filtering and standard robust detrending create artifacts that result in the displacement of multivariate patterns into activity silent periods, particularly apparent in temporal generalization analyses, and especially in combination with baseline correction. We show that trial-masked robust detrending is free from such displacements. Comparison with existing method(s): Temporal displacement may emerge even with modest filter cut-off settings such as 0.05 Hz, and even in regular robust detrending. However, trial-masked robust detrending results in artifact-free decoding without displacements. Baseline correction may unwittingly obfuscate spurious decoding effects and displace them to the rest of the trial. Conclusions: Decoding analyses benefit from trial-masked robust detrending, without the unwanted side effects introduced by filtering or regular robust detrending. However, for sufficiently clean data sets and sufficiently strong signals, no filtering or detrending at all may work adequately. Implications for other types of data are discussed, followed by a number of recommendations.

Original languageEnglish
Article number109080
Pages (from-to)1-18
Number of pages18
JournalJournal of Neuroscience Methods
Early online date27 Jan 2021
Publication statusPublished - 15 Mar 2021


This study was funded by the European Research Council under grant number grant number ERC-2013-CoG 615423 , as well as by the Dutch Research Council (NWO) under grant number 453-16-002 , both awarded to CNLO.

FundersFunder number
Seventh Framework Programme615423
European Research Council
Nederlandse Organisatie voor Wetenschappelijk Onderzoek453-16-002


    • Decoding
    • EEG
    • High-pass filtering
    • MEG
    • Multivariate pattern classification
    • MVPA
    • Preprocessing
    • Robust detrending


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