SPMers help!
I am a new spm user, and I trying to come up with a fMri experimental model
and contrast. Please see if my logic is at fault/imcomplete. I have tried
your on line tutorials and mailing list archives.
My experiment consists of on (stimulus) and off times. In terms of frames,
the breakdown is
Condition Frames length
OFF 1-13 13
ON 14-53 40
OFF 54-93 40
ON 94-133 40
OFF 134-173 40
ON 174-213 40
OFF 214-253 40
ON 254-293 40
OFF 294-319 25
My first problem is with the experimental model. I'm looking for a checkered
pattern ie
M
M
M
M
but have not achieved one when I fill SPM in as follows...
Interscan interval 2.24
scans 319
trails 2
SOA variable
vector on 14 94 174 254
vector off 1 54 134 214 294
NO variable durations
epoch lengths on 40
epoch lengths off 13 40 40 40 25
regressors 0
PROBLEM, when I look at the fmri design for off, epoch lenth for off is
13... not 13 40 40 40 25... Why is that....?
Remedy... have three variables with the first being just 1-13 (off)
The second being the on's
The third being the rest of the off's
Problem two (clarification)...
I now want to take my model and form contrasts. I have 10 normals and I
would like to compare to each and every diseased...
would the contrasts be
-1/10 0 <---nine more of these.... 1 0
note -1/10 represents the on period
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