LLN, le 6/06/07
Dear Pete and the others,
Thank you for your quick reply. I must confess that I don't see
clearly how to enter the 6 VOIs in later steps. It doesn't seem
possible to select more than 1 VOI when creating the PPI structure,
so I guess I need to create 6 different PPI_name.mat, one for each
run. Right? But then what? Do I load the 6 PPI_name.mat in one
analysis (and if so, how?) or do I run 6 different analyses for each
subject? And then, how do I combine these results at the individual
and group level?
Thanks in advance for any help,
Mauro
>Mauro,
> You have to create a different ROI for each of your 6 sessions,
>then because you have to enter each individually, the sessions
>aren't replications. I think you are plugging in the same voi signal
>from one run into all runs, and that's not correct.
>Hope that helps,
>Pete
>
>On Wed, 6 Jun 2007, PESENTI Mauro wrote:
>
>>LLN, le 6/06/07
>>
>>Dear all,
>>
>>I have 2 questions concerning PPI analyses.
>>
>>(1) I have a fMRI experiment with 6 sessions by subject. When
>>constructing the individual VOI, SPM asks "which session". What
>>should I answer here if I want to take into account the 6 sessions?
>>
>>
>>(2) Later on the process, when constructing the design matrix, SPM
>>asks if "sessions are replications". I notice that the results are
>>totally different
>>
>>- if I say "yes" and enter one single series of onset vectors,
>>- or if I say "no" and enter six times the very same series of onset vectors.
>>
>>(Note that if you do this on a first-level individual analysis, you
>>get exactly the same results.)
>>
>>Is there a reason for such a difference at this step? DFs, search
>>volume and number of voxels are similar, FWHM and resels are
>>slighly different, but I don't see how this could change the
>>results that much.
>>
>>
>>Any ideas? Thanks in advance for any help,
>>
>>Mauro Pesenti
--
_____________________________________
Help fighting hunger: http://www.hungersite.com
Just click your mouse and sponsors of The Hunger Site donate a
serving of food to a person in need - at no cost to you.
______________________________________
Mauro PESENTI
Research Associate, National Fund for Scientific Research (Belgium)
Unite de Neurosciences Cognitives
Departement de Psychologie
Universite Catholique de Louvain
Place Cardinal Mercier, 10
B-1348 Louvain-la-Neuve
tel.: +32 (0)10 47 88 22
fax: +32 (0)10 47 37 74
E-mail: [log in to unmask]
http://www.nesc.ucl.ac.be
http://www.nesc.ucl.ac.be/mp/pesentiHomepage.htm
|