[FieldTrip] ICA+frqanalysis questions

Alexander J. Shackman shackman at wisc.edu
Tue May 24 04:00:34 CEST 2011


And for a related perspective, see

McMenamin, B. W., *Shackman, A. J.*, Greischar, L. L. & Davidson, R. J.
(2011). Electromyogenic artifacts and electroencephalographic inferences
revisited, *Neuroimage**, 54*, 4-9.

http://psyphz.psych.wisc.edu/~shackman/mcmenamin_shackman_ni2011.pdf


On Mon, May 23, 2011 at 8:07 PM, Joseph Dien <jdien07 at mac.com> wrote:

> 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 Dien
> E-mail: jdien07 at mac.com
> Phone: 301-226-8848
> Fax: 301-226-8811
> http://homepage.mac.com/jdien07/
>
>
>
>
>
>
>
>
>
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>


-- 
Alexander J. Shackman, Ph.D.
Wisconsin Psychiatric Institute & Clinics and
Department of Psychology
University of Wisconsin-Madison
1202 West Johnson Street
Madison, Wisconsin 53706

Telephone: +1 (608) 358-5025
Fax: +1 (608) 265-2875
Email: shackman at wisc.edu
http://psyphz.psych.wisc.edu/~shackman
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