Hi all, I am a new user of SPM, and I have some basic questions about
setting up fMRI stats models. I would like some assurance that I am
setting the model correctly as this is a fundamental step for the
analysis. Thank you.
This is the info of the study:
TR=3.5s
2 conditions, ABAB....
6scans/condition X 2cond X 6cycles= 72scans
First "A" actually starts in scan #4 and 75scans were collected, and scans
#1, #2, #3 were discarded before spatial norm.
Therefore, our scans actually labelled as snxxx04.img .... snxxx75.img
before the statistics.
Here's how I specified for a fixed SOA fMRI model:
TR = 3.5
72 scans
2 trials (A, B)
Stachastic Designs = NO
SOA for "A" = 12
Time to first trial for "A" = 0
SOA for "B" = 12
Time to first trial for "B" = 6
Parametric modulation = NONE
Epoch, Fixed Box-car responses
Convolve with hrf = YES
Temporal derivative = NO
Epoch lengths for both "A" and "B" = 6
No interaction, 0 user's specified regressor
When I did the estimation, I selected scans #4-#75 only.
My questions:
1. Did I throw away the first three scans correctly, so that the
estimation did not use these scans and the rest of the scans are put into
the correct condition? When I looked at the "design image" of the stats
analysis, it's hard to tell if the images were lined up properly or not.
2. What does temporal derivative do? The model looked so different
with this option. How do I set up contrasts for this?
Sincerely,
Simon Au-Young
M.Sc. Student
University of British Columbia
|