[FieldTrip] ICA+frqanalysis questions

Joseph Dien jdien07 at mac.com
Tue May 24 03:07:57 CEST 2011

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.



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/
> _______________________________________________
> fieldtrip mailing list
> fieldtrip at donders.ru.nl
> http://mailman.science.ru.nl/mailman/listinfo/fieldtrip


Joseph Dien
E-mail: jdien07 at mac.com
Phone: 301-226-8848
Fax: 301-226-8811

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