[Eeglablist] Data Processing Steps for ICA?

[Paul Yu-Chun Chang]

Dear All,

I have 32-channel Neuroscan recordings (ca. 1 hr per subject) and am
recently trying to use ICA to remove blinks and eye movements from the data
(EEGLAB version 12.0.2.4b). After checking out some relevant
discussions/wiki pages/tutorials I find myself however still a bit confused
(particularly regarding re-referencing, baseline correction, and channels
to be included when running ICA) and am having some further questions. I'd
really appreciate your help.

Some essential steps as I understand now involve (pls correct me if I'm
wrong):

1. Reject bad epochs/channels to prune the data.
(source: http://sccn.ucsd.edu/wiki/Chapter_09:_Decomposing_Data_Using_ICA ;
http://sccn.ucsd.edu/eeglab/workshop06/handout/Practicum_3_ICA_Process.pdf)
2. Train ICA firstly on 1 Hz high-pass filtered pruned dataset.
3. Apply ICA weights to the same subject's 0.1 Hz high-pass filtered data
and evaluate components.
(source: http://sccn.ucsd.edu/pipermail/eeglablist/2011/004424.html)
4. Interpolate bad channels.

I'm however not so clear about:

1. When to perform base-line correction:
It seems most people suggest not to do it before ICA training based on
Groppe's 'split-half' paper:
http://sccn.ucsd.edu/pipermail/eeglablist/2010/003080.html
http://sccn.ucsd.edu/pipermail/eeglablist/2014/008854.html
But there are some counterarguments:
http://sccn.ucsd.edu/pipermail/eeglablist/2012/005513.html
So I guess it's still better to do it after ICA?

2. When and how to perform re-referencing:
It seems I should re-reference to average before ICA, but there seems to be
some counterarguments, too:
http://sccn.ucsd.edu/pipermail/eeglablist/2014/008309.html
http://sccn.ucsd.edu/pipermail/eeglablist/2014/008854.html
http://sccn.ucsd.edu/pipermail/eeglablist/2003/000090.html

I'm not pretty sure whether to include EOG channels either, as there seems
to be pros and cons:
http://sccn.ucsd.edu/pipermail/eeglablist/2014/008854.html
http://sccn.ucsd.edu/pipermail/eeglablist/2007/001801.html

Also is it all right to use average of M1/M2 (mastoid sites) for
re-referencing instead? Should M1/M2 be included for ICA training?

Many thanks!

Paul








-- 

Paul Yu-Chun Chang
Graduate School Language & Literature Munich - Class of Language
Ludwig-Maximilians-Universität München
Schellingstraße 10
80799 München, Deutschland
Email: Y.Chang at lipp.lmu.de
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