[Eeglablist] ica cleaning: removing epochs or components?

Jenny-Charlotte Baumeister baumeist at sissa.it
Wed Nov 5 02:43:02 PST 2014


Hi everyone,

I have a question regarding the cleaning after the ica. I cleaned my 
continuous data (by rejecting periods with movement artifacts after 
visual inspection), next I epoched the data and ran the ica on this (128 
channels, 650 epochs of 1sec at 256Hz).  It turns out that I have 
several components that account for only one electrode in single epochs.
I recorded from 128 electrodes and the experiment was very long so it 
seems natural to me that sometimes one electrode for a short time period 
shows improbable activity and goes back to normal after 1 epoch or so.
Now I read that after the ica I should go on and clean the epochs but 
not yet remove any components.  I read that I should do so only after I 
ran the second ica on the pruned data. But that seems like a "waste" to 
me since I would have to take out epochs that are actually fine but 
where just one electrode is out of range. Also interpolating the 
affected electrodes over all trials doesn't seem like a good idea to me 
since most of the time the electrode shows abnormal activity only for a 
brief time window.
So I was wondering whether it would actually make sense to generously 
remove all components that are associated with one crazy electrode at 
one time point, and then run the ica again instead of deleting the whole 
epoch.
Alternatively, I was wondering about interpolating broken electrodes in 
specific epochs only - is that appropriate and if yes how can it be 
done?

I would be very grateful for any suggestions and input on this!

Thanks a lot in advance
Jenny


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