Hi FSL experts!
I have a question about my analysis in FEAT and which level I should combine my EVs at. At the first level I have 6 EVs: posHit, posMiss, neuHit, neuMiss, negHit, and negMiss and my experiment has 9 runs. The contrast that I am interested in right now is pos vs. neu (so posHit+posMiss vs neuHit+neuMiss). Currently I model each of this EVs at the first level and then combine the COPEs at the second level for this contrast. So if after the first level posHit=COPE1, posMiss=COPE2, neuHit=COPE3, and neuMISS=COPE4, then in the second level I would input run1/COPE1, run2/COPE1, run1/COPE2, run2/COPE2 etc and have the statistical model like an unpaired t-test instead of an average.
My question is if it would be better do just do the comparison at the first level and then average at the second when I combine runs. So if posHit=EV1, posMiss=EV2, neuHit=EV3, and neuMiss=EV4, set up the contrast for each run as "1 1 -1 -1 0 0." Then at the second level I would just average that COPE across runs. Which is the better way to do this analysis and is there a difference between doing this at the first or second level?
I can send an example FEAT file if it would make more sense. Thanks in advance!
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