[Mne_analysis] 50Hz artefact for time frequency analysis

Elisabeth Fonteneau ef309 at cam.ac.uk
Wed Oct 8 07:30:40 EDT 2014
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Hi all,

Thanks for your reply,

Indeed the artefacts are coming from the cHPI (I did not say that it is not
picking up the electrical mainline)

But here is a snapshot (see files in the link below) of one participant/part
with the artefact

You have view of few electrodes and this is raw data 

The green line correspond to the start of the cHPI

You could see that before some electrodes were bad and remain unchanged

However some EEG were good before and with cHPI they have picked up some
high frequency

Also In general you could see that all EEG picked up some level of artefacts

I gave you also a plot for this subject/part of frequency decomposition

The EEG have 50z, 150z & around 330Hz

See files in art2/art4

https://www.dropbox.com/sh/hm7pdbhoc98yxf2/AABlCIdmLs4sWHw3W0sHesYGa?dl=0

 

Elekta is aware about this problem as it was recurrent in our recent
recordings and they are investigating

 

For the analysis,

I started to use a notch filter and it seems that it is removing the
artefacts as I would like (filtering the 3 sensors together)

However by comparing the unfilter vs notch filter data

I noticed that the filter data have another low frequency component added
(around 10Z) , effect present in the Mag

See figure art5 in the same dropbox..

 

I am using MNE_python for this notch filter with the command

raw.notch_filter(np.arange(50, 251, 50), method='fft', n_jobs=4)

 

any tips for this low frequency band addition?

 

 

 

Thanks for your answers

Elisabeth

 

 

 

__________________________________________________________

 

Dr Elisabeth Fonteneau

Neurolex Group

Department of Psychology

University of Cambridge

Downing Street, Cambridge CB2 3EB, UK

Phone: +44 1223 333 548

Email:  <mailto:ef309 at cam.ac.uk> ef309 at cam.ac.uk

Web:  <http://www.neurolex.psychol.cam.ac.uk/directory/ef309@cam.ac.uk>
www.neurolex.psychol.cam.ac.uk/directory/ef309 at cam.ac.uk

 

 

 

 

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