[Eeglablist] running ICA a second time

[Tarik S Bel-Bahar]

cheers. see also this recent article if you haven't yet from Makeig et al
that supports the idea that ICA is better than PCA at finding realistic eeg
sources. Just search on the web at PLos if the link is scrubbed.

*PLOS ONE*: Independent EEG Sources Are
Dipolar<http://www.plosone.org/article/authors/info%3Adoi%2F10.1371%2Fjournal.pone.0030135;jsessionid=3834349B9EE3031E0764F6666B59FEC2>
 www.*plosone*.org/.../info%3Adoi%2F10.1371%2Fjournal.p*on*...


On Wed, Feb 20, 2013 at 5:10 AM, Veerle ROSS <veerle.ross at uhasselt.be>wrote:

> Dear Tarik****
>
> Thank you for your quick response.****
>
> I will look into the ADJUST plugin and the other points you mention.****
>
> Best Veerle****
>
> ** **
>
> *From:* Tarik S Bel-Bahar [mailto:tarikbelbahar at gmail.com]
> *Sent:* woensdag 20 februari 2013 2:01
> *To:* Veerle ROSS
> *Cc:* eeglablist at sccn.ucsd.edu
> *Subject:* Re: [Eeglablist] running ICA a second time****
>
> ** **
>
> Greetings Ross:****
>
> ** **
>
> Some brief responses to your questions below, I hope they are helpful.
> I've numbered the responses according to your questions.****
>
> ** **
>
> 0. if you have note please search eeglab list archives where you will
> definitely find some past discussions.****
>
> PLease read through the articles about cleaning with eeglab, which you can
> easily find on Google Scholar.****
>
> Check out the eeglab tutorial and wiki, particular guidelines. ****
>
> ** **
>
> 1a. You can use PCA (see post within last 2 months on this subject based
> on a "should I PCA and if so what is best method")****
>
> Reducing by PCA may decrease the "validity" or "truthfullness" of your
> ICs. ****
>
> Check Joseph Dien's PCA toolkit for some principled methods to do PCA. ***
> *
>
> ** **
>
> 1c. You should find similar ICs after 2 ICAs, as the second ICA
> decomposition. The ones in the second ICA should be cleaner and more
> accurate.****
>
> Some people just publish their first ICA results, as it is not always the
> case that you gain much from a second ICA.****
>
> ** **
>
> 2a. I assume you have properly cleaned your data before the first ICA. ***
> *
>
> My recommendation is, if you want to do a second ICA, first consider doing
> what eeglab documentation recommend: ****
>
> after your first ICA, then do artifactual epoch rejection using ICA-based
> rejection, then do a second ICA.****
>
> ** **
>
> 2b. it's not clear what your question is, perhaps there is a word missing
> in your question.****
>
> You could remove noisy or blink or other artifactual components if you
> want to, go ahead****
>
> and do a second ICA, and compare the results to doing it via the method
> suggested in the response to 2a above.****
>
> ** **
>
> also:****
>
> Check out the the ADJUST plugin (amongst others for a variety of cleaning
> techniques). ****
>
> &****
>
> Note there are least three camps:****
>
> a. those who use ICA just to deblink or otherwise clean their data, and
> then they reconstruct the EEG and do their analyses outside of ICA space.
> [ergo, ICA is a cleaning tool]****
>
> b. those who use ICA to get ICs that reflect brain dynamics and (often)
> established ERP components, they do their analyses on ICs [ergo, ICA gives
> real brain dynamics]****
>
> c. those who use PCA (with or without ICA) to decompose ERPs into spatial
> (and/or) temporal components, they do their analyses on PCs****
>
> ** **
>
> ** **
>
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