[Eeglablist] Are the results more significant on the scalp or inside brain?
Michal Vavrecka
vavrecka at fel.cvut.cz
Tue May 13 14:21:25 PDT 2014
Dear Makoto,
thanks for your answer.
On 13.5.2014 03:14, Makoto Miyakoshi wrote:
> Dear Michal,
>
> That's a simple but deep question.
> Theoretically the difference between condition can't be smaller in ICA
> recults since canceling happens in the mixing process and not the
> other way around (like the law of entropy?)
>
> However, I believe a major problem in comparing channels with ICs is
> component selection. The question is how you guarantee that the ICs
> you choose is a right representative (projecting source) to the
> channel? What if some subject don't have such ICs? What if some
> subjects have multiple of such ICs (subspace)?
>
This is good argument.
> One way to investigate this problem is run pvaf analysis (you have
> pvaftopo under EEGLAB plugin manager)
> I have an experience of computing the pvaf analysis across subjects
> per cluster (unpublished data), and the result showed very large
> standard deviations... it was like mean 30% and SD=30, range 5-80.
> This means a cluster can explain a channel activity (in my result, of
> course) only by 30%, and there are huge inter-subject variance.
I am going to check this functions in near future
>
> This being said, I think it is still ok to stay optimistic and take
> the theoretical conclusion. You haven't observed horrendously
> contradicting results, have you?
No, the results are ok, I am just thinking how to interpret the smaller
effect (significant periods) in DIPFIT results.
Michal
>
> Makoto
>
> 2014-05-12 14:02 GMT-07:00 Michal Vavrecka <vavrecka at fel.cvut.cz
> <mailto:vavrecka at fel.cvut.cz>>:
>
> Hello,
>
> I do have few simple questions and I am curious about your
> intuitions and arguments:
>
> I am finishing the paper where I did group analysis of two
> cognitive states. I visualized both scalp maps and dipoles and
> their statistical tests. Both visualization are based on fieldtrip
> monte carlo permutation with cluster based statistics (correction
> for multiple comparison). I would like to interpret the difference
> between results on the scalp and inside the brain (DIPFIT). What
> are your intuitions:
>
> Should the effect be stronger (in terms of more statistically
> significant electrodes (dipoles) and timeperiods) on scalp
> electrodes or in DIPFIT clusters?
>
> How to interpret the stronger effect on the scalp?
> Does the ICA and DIPFIT calculation somehow weaken the ERSP
> difference?
> My intuition is opposite as the source reconstruction has to clean
> the noise and strengthen the effect that should result in more
> statistically significant timeperiods in the spectrograms compared
> to scalp data?
> Is there any paper that compares these two approaches?
>
> Thanks for your answers.
>
> Michal
>
>
>
> --
> Michal Vavrecka
> assistant professor
> Biodat Research Group
> Incognite Research Unit
> FEE CTU
> Karlovo nam. 13
> Prague 2
> phone: +420224357609 <tel:%2B420224357609>
> cell: +420608661977 <tel:%2B420608661977>
> personal: http://bio.felk.cvut.cz/~vavrecka/
> <http://bio.felk.cvut.cz/%7Evavrecka/>
> groups: http://incognite.felk.cvut.cz/
> http://bio.felk.cvut.cz/
>
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>
>
> --
> Makoto Miyakoshi
> Swartz Center for Computational Neuroscience
> Institute for Neural Computation, University of California San Diego
--
Michal Vavrecka
assistant professor
Biodat Research Group
Incognite Research Unit
FEE CTU
Karlovo nam. 13
Prague 2
phone: +420224357609
cell: +420608661977
personal: http://bio.felk.cvut.cz/~vavrecka/
groups: http://incognite.felk.cvut.cz/
http://bio.felk.cvut.cz/
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