[FieldTrip] Removing power line

[Emilie Caspar]

Dear Fieldtrippers,

I recently acquired EEG data in Rwanda in complicated testing conditions, especially for the power line : we were testing in rural villages with a single electrical system for the whole village. Our signal is thus parasited by what the villagers were plugging on the electrical system (so probably nonstationary noise) during the testing. The electrical system was also very rudimentary and not correctly grounded.

Usually, I use the following command in Fieldtrip to remove the 50H or 60 Hz power line and it works quite well. Here, it worked for roughly 70% of our acquired data, but it does not work for all the data acquired.

    cfg= [];
    cfg.dftfilter = 'yes';
    cfg.dftfreq = [50 60 100 120 150 180];
    cfg.dftreplace = 'neighbour'; 
    cfg.dftbandwidth = [2 2 2 2 2 2];
    cfg.dftneighbourwidth = [2 2 2 2 2 2];
    data_intpl = ft_preprocessing(cfg, allData_preprosses);


When I look at the graphs (see figure attached), it really looks like it’s a 60Hz noise, but it seems that the dftfilter function does not remove it. We are certain it’s power noise because when the electricity was cut off because of a storm or else, and we were thus only relying on the batteries to collect our data, the signal was perfect. So in theory we should be able to remove it but we have no cue of what other possibilities to try. Perhaps it’s because the noise is non stationary and dftfilter does not account for that? I know some residual power noise can stay after a dftfiltre, but here it does not remove anything.

Thanks a lot for the help, 

Emilie


---------------------------------------------
Prof. Dr. Emilie Caspar

Associate Professor 

Department of Experimental Psychology, Ghent University
office: Henri Dunantlaan, 2 - Floor 2, Room 94

lab’s website: https://moralsocialbrain.com/ <https://moralsocialbrain.com/> 
personal website: https://emiliecaspar.home.blog/ <https://emiliecaspar.home.blog/>
Université libre de Bruxelles (office & contact): DB10.138 / +32 2 650 32 95


-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mailman.science.ru.nl/pipermail/fieldtrip/attachments/20211003/83dd0597/attachment.htm>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: PowerLine.jpg
Type: image/jpeg
Size: 37857 bytes
Desc: not available
URL: <http://mailman.science.ru.nl/pipermail/fieldtrip/attachments/20211003/83dd0597/attachment.jpg>