[FieldTrip] ICA+frqanalysis questions

[odelia nakar]

Thank you all- Joe, Alexander and David, it is indeed very helpful and enlightening. 
I actually don't have any stimulus, but I wasn't aware of the hidden EMG. 
Have a good day (or night :))!
Odelia.
From: jdien07 at mac.com
Date: Mon, 23 May 2011 21:07:57 -0400
To: fieldtrip at donders.ru.nl
Subject: Re: [FieldTrip] ICA+frqanalysis questions



I agree with David's reasoning.  You may find the following article to be of help as well in understanding the issues involved:
Dien, J., Khoe, W., & Mangun, G. R. (2007). Evaluation of PCA and ICA of simulated ERPs: Promax versus Infomax rotations. Human Brain Mapping, 28(8), 742-763.
Cheers!
Joe
On May 23, 2011, at 11:57 AM, David Groppe wrote:Hi Odelia,
   When you use ICA (or any other spatial filter) to correct for EEG
artifacts, you're going to distort your data some by removing true EEG
activity in addition to the artifact (for an explanation, see:
http://www.cogsci.ucsd.edu/%7Edgroppe/PUBLICATIONS/GroppeCSO2008.pdf).
 So to minimize distortion, it would be better not to apply ICA
artifact correction to artifact-free data.  However, if the frequency
of the artifact differs across experimental conditions, it could
confound your analysis.  For example, I suspect people blink more
often to targets in an oddball experiment than standards.  Thus if you
apply ICA only to blinky trials, you could find a difference between
the EEG response to standards and targets that simply reflects the
fact ICA removed more EEG activity in the target trials (i.e., it
wouldn't reflect a true difference in neural processing).
      hope this helps,
         -David

On Mon, May 23, 2011 at 1:44 AM, odelia nakar <odidodi at hotmail.com> wrote:
Hi all,

I'm troubled by the fact that when I use ICA for blinks\eyes movements
removal, I remove the relevant components also from trials that do not
contain blinks\eyes movements. In order to avoid this bias we thought to
combine the data before ICA ("data" structure) with the data after ICA
("dataica" structure), only in specific trials, as follows:

datall=dataica;
datall.trial=data.trial;
datall.time=data.time;
blinks=[2 4 5 8 bla bla 156];
for ind=1:length(blinks)
     datall.trial{1,blinks(ind)}=dataica.trial{1,blinks(ind)};
end

To my first question: I just wanted to check that there is no problem with
that, or any reason not to use it.

Another issue- I use motor learning task, and I'm trying to understand what
happens through the process, in terms of power-frequency changes through the
process. How would you recommend that I'd use the ft_freqanalysis function?
What method to use (or what do I need to consider when choosing the method
field)?


Thanks a lot,
Odelia.

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-- 
David Groppe, Ph.D.
Postdoctoral Researcher
Kutaslab
Dept. of Cognitive Science
University of California, San Diego
http://www.cogsci.ucsd.edu/~dgroppe/

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Joseph DienE-mail: jdien07 at mac.comPhone: 301-226-8848Fax: 301-226-8811http://homepage.mac.com/jdien07/







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