[FieldTrip] ICA+frqanalysis questions
odelia nakar
odidodi at hotmail.com
Wed Jun 1 09:10:30 CEST 2011
Hi all,
Thank you all for the discussion. I'm sorry I response only now, I went on a vacation...
I actually didn't want to run the ICA on trials with blinks, rather on all trials, but to remove the component only for trials with a blink. Your critics concern my idea as well, since if I have any kind of correlation between condition and blink I might yield a difference that does not exist between conditions...
Considering your suggestion, Mahesh, unfortunately I don't have EOG recording for this experiment.
Thanks again for the discussion,
Odelia.
Date: Fri, 27 May 2011 00:32:01 -0400
From: mahesh.casiraghi at gmail.com
To: yuvharpaz at gmail.com; fieldtrip at donders.ru.nl
Subject: Re: [FieldTrip] ICA+frqanalysis questions
Dear Yuval and discussion group,
it seems to me that what you are proposing is getting close to what proposed by the hybrid approach of regica described here:
Manousos A. Klados, Christos Papadelis, Christoph Braun, Panagiotis D. Bamidis, REG-ICA: A hybrid methodology combining Blind Source Separation and regression techniques for the rejection of ocular artifacts, Biomedical Signal Processing and Control, In Press, Corrected Proof, Available online 16 March 2011, ISSN 1746-8094, DOI: 10.1016/j.bspc.2011.02.001.
They suggest to selectively run regression based AR only on those components which correlate with EOG signals. This makes sense to me and I have been trying to experiment that on some old data, although with no clear conclusions yet. It may be worth a try for Odelia: Anybody out there with some insights for this - or maybe a similar - approach?
Cheers,
Mahesh
Mahesh M. CasiraghiPhD candidate - Cognitive Sciences
Roberto Dell'Acqua Lab, University of PadovaPierre Jolicoeur Lab, Univesité de Montréal
mahesh.casiraghi at umontreal.ca
I have the conviction that when Physiology will be far enough advanced, the poet, the philosopher, and the physiologist will all understand each other.
Claude Bernard
On Thu, May 26, 2011 at 11:40 PM, Yuval Harpaz <yuvharpaz at gmail.com> wrote:
Dear discussion groupDid anybody consider smoothing or filtering the component trace before rejecting it?
it seems that the added noise to no-blink trials is in a frequency higher than that typical to blinks. what if we evaluate the component weight, creating a trace for the eyeblink component for every trial, then bandpass filter the blink trace , say 0.1-25Hz, and only then remove the component from the data?
yuval
On 27 May 2011 06:16, Joseph Dien <jdien07 at mac.com> wrote:
Stefan, just to be clear, I don't think any of us were saying not to use ICA to correct blinks. David was just saying that there are potential concerns when one only applies the ICA to the blink trials rather than to all the trials. I myself use EEGlab's infomax implementation in the automatic eyeblink correction tool of my EP Toolkit (http://sourceforge.net/projects/erppcatoolkit/).
Now that said, I should add a little more nuance to my response. One of the things I observed (or rather, that Tim Curran pointed out to me) is that when you apply ICA to remove eyeblink artifacts in this manner, it can actually substantially increase the noise level in the data, so for the trials without eyeblinks it can have a considerable cost. So in order to balance the cost/benefit ratio, what I did was to include a trial by trial criterion that the putative eyeblink factors would only be removed if doing so reduced the overall variance of the trial. This approach does still have some potential for causing the concerns that David raises but not as much as only applying the ICA to blink trials since it does end up getting applied to non-blink trials too. This does mean that one should be cautious about any apparent effects in the artifact corrected data that are centered around the eyes (that have a blink topography) but that goes without saying in any case. So anyway, I agree, it's not perfect but seems to be the best available option.
Cheers!
Joe
On May 24, 2011, at 3:11 AM, Stefan Debener wrote:
Hi Odelia,
I have a slightly different opinion here. It is certainly true that
any filter has the tendency to distort data (with distortion I mean
that data consists of a mixture of some wanted, true signal and some
unwanted signal, and that the removal of the unwanted part of the
signal is neither complete nor specific). In our lab we regularly
use ICA for artefact removal (and more), and the benefit/gain is
clearly are much larger than the distortion. In fact there are a
number of examples out showing that currently only ICA (or related
tools) can recover the study of (a substantial fraction of the
wanted) EEG signal (but again, it is NOT a perfect tool at all), in
particular in cases where other means of SNR enhancement don't work
well (averaging, spectral analysis). I am happy to provide
references if you are interested...
For the evaluation of outcome it would be reasonable to not evaluate
the ERP alone, as this could be misleading. Better evaluate the
sensitivity and specificity of an eye blink attentuation approach on
the single trial (and single subject) level, this will give you good
insight. And it is worth keeping in mind that the preprocessing of
the data (among other issues, like the quality of the recording and
so on) largely determines the quality of the output (for some
introduction you may look up chapter 3.1 in Ullsperger &
Debener, 2010, Simultaneous EEG and FMRI, Oxford University Press).
Just by a different preprocessing ICA output could vary between crap
and excellent unmixing. Thus a poor ICA eye blink attenuation would
make me a bit suspicious...
Best,
Stefan
Am 5/24/11 4:00 AM, schrieb Alexander J. Shackman:
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.
_______________________________________________
fieldtrip mailing list
fieldtrip at donders.ru.nl
http://mailman.science.ru.nl/mailman/listinfo/fieldtrip
--
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
http://homepage.mac.com/jdien07/
_______________________________________________
fieldtrip mailing list
fieldtrip at donders.ru.nl
http://mailman.science.ru.nl/mailman/listinfo/fieldtrip
--
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
_______________________________________________
fieldtrip mailing list
fieldtrip at donders.ru.nl
http://mailman.science.ru.nl/mailman/listinfo/fieldtrip
--
Prof. Dr. Stefan Debener
Neuropsychology Lab
Department of Psychology
University of Oldenburg
D-26111 Oldenburg
Germany
Office: A7 0-038
Phone: +49-441-798-4271
Fax: +49-441-798-5522
Email: stefan.debener at uni-oldenburg.de
_______________________________________________
fieldtrip mailing list
fieldtrip at donders.ru.nl
http://mailman.science.ru.nl/mailman/listinfo/fieldtrip
_______________________________________________
fieldtrip mailing list
fieldtrip at donders.ru.nl
http://mailman.science.ru.nl/mailman/listinfo/fieldtrip
--
Y.Harpaz
a link to the BIU MEG lab:
http://faculty.biu.ac.il/~goldsa/index.html
"Many were increasingly of the opinion that they'd all made a big
mistake in coming down from the trees in the first place. And some said
that even the trees had been a bad move, and that no one should ever
have left the oceans". Douglas Adams
_______________________________________________
fieldtrip mailing list
fieldtrip at donders.ru.nl
http://mailman.science.ru.nl/mailman/listinfo/fieldtrip
_______________________________________________
fieldtrip mailing list
fieldtrip at donders.ru.nl
http://mailman.science.ru.nl/mailman/listinfo/fieldtrip
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mailman.science.ru.nl/pipermail/fieldtrip/attachments/20110601/ec53b370/attachment.html>
More information about the fieldtrip
mailing list