[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 per cluster (unpublished data), and the result showed very large 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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