[Eeglablist] Are the results more significant on the scalp or inside brain?

[Makoto Miyakoshi]

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)?

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cluster (unpublished data), and the result showed very large standard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.

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?

Makoto

2014-05-12 14:02 GMT-07:00 Michal Vavrecka <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
> cell: +420608661977
> personal: http://bio.felk.cvut.cz/~vavrecka/
> 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
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