[Eeglablist] ica problems

Bethel Osuagwu b.osuagwu.1 at research.gla.ac.uk
Tue Jun 17 12:25:20 PDT 2014

Hi Cheng,
You should not delete components if you are running the second ICA because doing so reduces the rank/information in your data. Normally when people do two ICAs, they use the 'activation' time series of the first ICA to find and remove uncommon noisy  epochs without deleting components. 
If you feel you have to delete component before the second ICA, then use PCA to reduce the dimension of your data (EEGLAB's ICA tutoriat will have information on how to do this).

From: eeglablist-bounces at sccn.ucsd.edu [eeglablist-bounces at sccn.ucsd.edu] On Behalf Of QuanCheng [ksak607155 at 163.com]
Sent: 17 June 2014 10:13
To: eeglab
Subject: [Eeglablist] ica problems

I am a novice  to eeglab and really need some help.

After reading the tutorials,I find it necessary to take a second ICA process.
When I proceed the first ICA and then use ADJUST to reject artifacts,the rest components seem normal.
However,when I finish the second ICA , some components look more like artifacts(contains large amount of high frequency waves),and  much worse than the rest components in the first ICA (after ADJUST).
I wonder whether the phenomenon is common and I will appreciate if anyone can explain on it.

Thanks a lot.

Quan Cheng
Beijing Institute Of Radiation Medicine
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