SPM experts,
I am a first time user of SPM and wanted to double-check my design to
ensure that I am performing my analysis correctly, especially since I am
not getting the results that I had anticipated. I am using SPM2.
Our study has 7 subjects so far (we are in the middle of the study and
trying to analyze what we have so far to use as pilot data). Each subject
is scanned twice and has condition 1 (C1) on one day and condition 2 (C2)
on the other day. On each day, the subject performs two runs of the same
task, which has two block conditions (A and B).
I performed a first level analysis for each subject on each visit (e.g.
Sub1, C1). I created contrast images that contrasted block A versus block
B. I then took these contrast images and entered them into a paired t-
test, where a pair consisted of 1) A-B contrast image for C1 and 2) A-B
contrast image for C2.
Just to clarify, it is my understanding that the p value and voxel extent
thresholds you put in for the t-test after the first level analysis has no
bearing on the con_* image that is created and used in the second level
analysis. Is this correct?
I am performing no masking and using very liberal p-values and cluster
values and am still not seeing much activation. Does this mean that my
data just doesn't have any significance or am I doing something wrong?
I hope I have been clear in my explanation and I greatly appreciate any
guidance.
Best Regards,
Rachel
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