Dear Stephan,
This problem is known. My understanding was that there is an inherent
limitation for how many subjects you can realign without getting rid
of all the dimensions of the sensor space. However if Rik says that
there was a change in that between SPM versions perhaps it deserves
another look. For now I would suggest either doing individual
inversions or doing group inversions for each subject with randomly
chosen ~8 other subjects. That will still maintain some group
constraints without getting into that dimensionality issue.
We know MSP is not ideal and even know some of the reasons for it and
there is ongoing work to improve it. But as any inverse solution it
works well for some people and doesn't work at all for others.
Best,
Vladimir
On Wed, May 2, 2012 at 7:49 PM, [log in to unmask] <[log in to unmask]> wrote:
> Dear SPM users,
>
> I tried to do a group inversion with neuromag MEG data (2 conditions, 18
> subjects). When I include MEGPLANAR I get 0 spatial modes and NaNs. For the
> MEG I get 1 spatial mode (if I invert individually I get 66 modes for MEG
> and 104 modes for MEGPLANAR). So, if I only use MEG to get a solution, I get
> for all subjects, conditions the same solutions (and a very unlikely one,
> beam former, MNE and LORETA get visual cortex activity, GS group inversion
> gets auditory activity that is equal for all conditions and subjects).
>
> I saw similar postings in the SPM list in 2010 and it was advised to wait
> for a newer SPM version. I have used the newest 2012 SPM version. I did tSSS
> with the MEG data, but I do not know if SPM applies the SSP vectors to the
> data (it shouldn't when using tSSS). Could this be the problem?
>
> Best,
>
> Stephan
>
> ________________________________________________________
> Stephan Moratti, PhD
>
> see also: http://web.me.com/smoratti/
>
> Universidad Complutense de Madrid
> Facultad de Psicología
> Departamento de Psicología Básica I
> Campus de Somosaguas
> 28223 Pozuelo de Alarcón (Madrid)
> Spain
>
> and
>
> Center for Biomedical Technology
> Laboratory for Cognitive and Computational Neuroscience
> Parque Científico y Tecnológico de la Universidad Politecnica de Madrid
> Campus Montegancedo
> 28223 Pozuelo de Alarcón (Madrid)
> Spain
>
>
> email: [log in to unmask]
> Tel.: +34 679219982
>
> El 02/05/2012, a las 20:03, Liam Mason escribió:
>
> Hi Carlos,
>
> Did you get any answer of if it is possible to extract %SC from a group of
> subjects? I'm afraid the only way I know is to do them iteratively as you
> say. If marsbar is able to do it from a second-level (group) SPM file, then
> would be keen to know!
>
>
> Liam
>
> ---
> School of Psychological Sciences
> University of Manchester
> 0161 275 2692
>
> ________________________________________
> From: SPM (Statistical Parametric Mapping) [[log in to unmask]] on behalf of
> Ming-Tsung Tseng [[log in to unmask]]
> Sent: 24 April 2012 18:14
> To: [log in to unmask]
> Subject: Re: [SPM] Compare 2 methods to extract %signal change in MarsBaR
>
> Hi Matthew,
>
> Excellent to get your clear explanation!!
>
> So I can use Method 2 to extract Beta values in a group of subjects, right??
>
> One more question: Since %SC and Beta value can both represent neural
> response in an ROI, which one is better?......I mean, if I want to extract
> %SC, I have to use Method 1 which will be performed subject by subject and
> time-consuming (or any time-saving way to get %SC within many ROIs in a
> group of subjects)?
>
> Thanks indeed!
>
> Carlos
>
>
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