Hello all,
Long story short, my question here is about the number of parameters in
my design matrix. It doesn't look like I'm getting the same number of
regressors as the number of conditions that I'm specifying, and so I
can't setup my contrasts properly. Below, I've elaborated....
I'm working with a rather large fMRI design. There are 16 scan
sessions, and each session contains a handful of events. There are 39
possible events but each session contains only 10 of each type at a max.
I managed to script together the fMRI model specification stage. For
each subject, the script creates a new fMRI model. It creates 1 session
for each of the 16 sessions, and then loads in the 39 condition names,
onsets, and durations from .mat files that I created. Each .mat file
contains a names, onsets, and durations cell variable that contains the
relevant onsets and such for that particular session. If an event does
not occur in a particular session, onsets and durations are equal to []
for that condition's cell. Finally, I include the rp_*.txt files that
come from the preprocessing, reslice & estimate stage as multiple
regressors, to control for motion parameters.
By my count then, each session has 39 conditions and 6 motion
parameters, that should mean 45 regressors per condition. My design
matrix should therefore include 720 regressors (45 regressors x 16
sessions). However, it seems to only include 112. If I look at my
design matrix, I seem to have 16 sessions [ S(n) counts up to 16 if I
look at the parameters ], but each session only seems to have 6
regressors (R1, R2... R6, again, from the design matrix). The 112
parameters then come from 6 regressors x 16 sessions, plus 16 constants.
So my question is, what have I done wrong? I know that 39 conditions is
a lot, but why am I not getting 39 regressors and only 6 for each condition?
Thanks in advance.
Cheers,
Jason
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