[FieldTrip] strange observations using ICA

weberi at staff.uni-marburg.de weberi at staff.uni-marburg.de
Thu Aug 9 09:26:25 CEST 2018

Dear FieldTrip community,

I have a question concerning some strange observations when using ICA.
In our lab we try to get rid of an EEG artefact induced by deep brain  
For this purpose we compute an ICA of our EEG-channels and sort the components
relative to their similarity (quantified using mutual information)  
with the raw artefact
measured  directly from the stimulator. We then successively remove  
the components
according to their mutual information and calculate the mean frequency  
spectrum of the
back-transformed corrected data. The artefact has a very defined  
frequency distribution
with peaks at multiples of 130 Hz.  With our approach, we would expect  
the artefactual
peaks to successively become smaller. However, this is not the case.  
While the peaks
ultimately become smaller after removal of several components, the  
artefactual power
even rises again after the first couple of components. How can this be  

Any insights would be much appreciated,

Best regards
Immo Weber

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