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
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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
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