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Front. Comput. Neurosci. | doi: 10.3389/fncom.2018.00082

Reducing the Effect of Spurious Phase Variations in Ongoing EEG Signals

 Daniel J. Strauss1, 2*, Zeinab Mortezapouraghdam1, 2 and Farah I. Corona-Strauss1, 2
  • 1Systems Neuroscience and Neurotechnology Unit, Saarland University, Germany
  • 2School of Engineering, University of Applied Sciences of the Saarland, Germany

The phase-reset model of oscillatory EEG activity has received a lot of attention in the
last decades for decoding different cognitive processes. Based on this model, the ERPs are
assumed to be generated as a result of phase reorganization in ongoing EEG. In addition,
the study of oscillatory EEG signals can be used to overcome limitations regarding the
study of segmented EEG data, i.e., ERPs. Measuring the level of instantaneous phase (IP)
synchronization has been used in numerous studies of ERPs as well as oscillatory activity for
a better understanding of the underlying neural activities. However, the reliability of results can
be challenged as a result of noise artefact in IP. Phase distortion due to environmental noise
artifacts as well as different pre-processing steps on signals can lead to generation of artificial
phase jumps. One of such effects presented recently is the effect of low envelope on the IP of
signal. It has been shown that as the instantaneous envelope of the analytic signal approaches
zero, the variations in the phase increase, effectively leading to abrupt transitions in the phase.
These abrupt transitions can distort the phase synchronization results as they are not related
to any neurophysiological effect. These transitions are called spurious phase variation. In this
study, we present a model to remove generated artificial phase variations due to the effect of
low envelope. The proposed method is based on a simplified form of a Kalman smoother, that
is able to model the IP behavior in narrow-bandpassed oscillatory signals. The method is not
only evaluated on synthetic data but also in experimental EEG measurements recorded using a
listening dichotic paradigm designed to assess auditory selective attention between an attended
and unattended conditions.

Keywords: instantaneous phase, Spurious Phase, Kalman smoother, phase synchronization, spontaneous activity

Received: 22 May 2018; Accepted: 12 Sep 2018.

Edited by:

Jonathan D. Victor, Weill Cornell Medicine, Cornell University, United States

Reviewed by:

Carmen C. Canavier, LSU Health Sciences Center New Orleans, United States
Surjo R. Soekadar, Klinik für Psychiatrie und Psychotherapie, Universitätsklinikum Tübingen, Germany  

Copyright: © 2018 Strauss, Mortezapouraghdam and I. Corona-Strauss. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

* Correspondence: Prof. Daniel J. Strauss, Saarland University, Systems Neuroscience and Neurotechnology Unit, Saarbrücken, Germany,