specifying individual lateralization in sourcestatistic

[Passaro, Antony D]

Hi Michael (or anyone else),

I had a question in regards to your comment in this email, specifically where you mention obtaining t-values from first level statistics. In the example on the Fieldtrip website, ft_sourcestatistics describes a method of obtaining the t-values when comparing conditions directly but I was wondering how it might be possible to obtain the t-values by using source statistics for a task-vs-basline comparison for one condition? More specifically, what would have to be changed in the example from the website (posted below)?

cfg = [];
cfg.dim         = source.dim;
cfg.method      = 'montecarlo';
cfg.statistic   = 'indepsamplesT';
cfg.parameter   = 'pow';
cfg.correctm    = 'cluster';
cfg.numrandomization = 1000;
cfg.alpha       = 0.05;
cfg.tail        = 0;
cfg.design(1,:) = [1:length(find(design==1)) 1:length(find(design==2))];
cfg.design(2,:) = design;
cfg.uvar        = 1; % row of design matrix that contains unit variable (in this case: trials)
cfg.ivar        = 2; % row of design matrix that contains independent variable (the conditions)

stat = ft_sourcestatistics(cfg, source);


Thank you very much for your help,
-Tony



-----Original Message-----
From: FieldTrip discussion list [mailto:FIELDTRIP at NIC.SURFNET.NL] On Behalf Of Michael Wibral
Sent: Friday, October 15, 2010 9:08 AM
To: FIELDTRIP at NIC.SURFNET.NL
Subject: Re: [FIELDTRIP] specifying individual lateralization in sourcestatistic

Hi Thomas,

I suggest you simply extract the power values from the results of sourceanalysis (or t-values if you already did a fisrt level statistics) and average them by hand in MATLAB - as ROI is known for each subject this should be easy (you have to extract the values by the voxel indices contained in your ROI. These in turn you can find in interactive mode source plotting if everything else fails). This way you end up with a single value per subject and condition. Afterwards you do a simple permutation test by hand in MATLAB. 

((The test for two conditions for example can be done this way:
1. concatenate all data in a vector D first data in one condition, then in the other) 2. compute your test metric between first and second half of D.
3. shuffle the entries of D: DS=D(randperm(length(D)); % creates a new D with shuffled entries by shuffling the indexes of the old one 4. compute your test metric for DS and remember it 5. Do 3+4 N times (e.g. >1901 times for accurate testing at alpha<0.05) 6. check where your original test metric obtained from D is in the distribution of the mtrices obtained from the DS.))


Hope this helps,
Michael

-----Ursprüngliche Nachricht-----
Von: "Thomas Hartmann" <thomas.hartmann at UNI-KONSTANZ.DE>
Gesendet: Oct 15, 2010 3:30:40 PM
An: FIELDTRIP at NIC.SURFNET.NL
Betreff: [FIELDTRIP] specifying individual lateralization in sourcestatistic

>  hi,
>i want to do a roi analysis on source data and average over the all the 
>voxels. the problem is that i am dealing with a lateralized effect that 
>i expect to show up either on the left or the right side of the same 
>structure. this lateralization is individual for each subject and known 
>a priori.
>is there any possibility to individually define, which side to take 
>into account for the statistics?
>
>thanks in advance,
>thomas
>
>--
>Dipl. Psych. Thomas Hartmann
>
>OBOB-Lab
>University of Konstanz
>Department of Psychology
>P.O. Box D25
>78457 Konstanz
>Germany
>
>Tel.: +49 (0)7531 88 4612
>Fax: +49 (0)7531-88 4601
>Email: thomas.hartmann at uni-konstanz.de
>Homepage: http://www.uni-konstanz.de/obob
>
>"I am a brain, Watson. The rest of me is a mere appendix. " (Arthur 
>Conan Doyle)
>
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See also http://listserv.surfnet.nl/archives/fieldtrip.html
and http://www.ru.nl/neuroimaging/fieldtrip.
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