[Eeglablist] Massimiliano Papera removing ICA component

[Tarik S Bel-Bahar]

Greetings M,

***we could use an opinion from an ICA/PCA expert here, but here are some
thoughts. *******
I have tried to keep it as clear, simple, and (hopefully) useful as
possible.

I assume you have done some cleaning before running your first ICA,
as per general pre-ICA guidelines.
If so, then your sequence of
first ICA, then reject some epochs using IC data,
then second ICA, then remove some bad components...
seems OK. This seems like a normal processing procedure.

So now you can analyze specific ICs,
or you can "reconstruct" your eeg data using only the remaining ICs,
and have "cleaner" EEG data for "normal" EEG analyses.

imho, I don't see why you want to re-run the ICA again now for the third
time.
If you do, you might get a slightly better decomposition,
but there should not be a significant change of ICs.

on your question about PCA, perhaps one of the experts can make a
suggestion,
but from my understanding, the PCA option is used when
A. the "dimensionality" and/or the "rank" of the data has been reduced via
some method,
and you want ICA to know this before running a new decomposiiton
B. or you want to "reduce" the total number of dimensions that ICA
generates,
for some other good reason. [see published articles on this point]

Last, I want you to know I am not 100% sure about whether or not you "have
to" run ICA with PCA options
when you are re-running ICA after having "dropped/removed" some components.
one previous eeglab list discussion:
http://sccn.ucsd.edu/pipermail/eeglablist/2012/004543.html

Good luck and let the list know of your success.
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