Hi all,
I've been combing through the archives and haven't found anything, so I was hoping someone could help.
I have a 3 x 2 design with condition (task1, task2, control) and set size (2, 4) as variables. I have parametric modulators for the task conditions, but not the control conditions (4 regressors).
Task Set pmod
1 1 1
2 1 1
3 1 0
1 2 1
2 2 1
3 2 0
I'm interested in main effects of task and set size, but also in the effect of the pmod overall.
So, at the first level, I modeled regressors for each condition (6), and each parametric modulator separately (4) (10 regressors overall).
At the second level, I specified factors for subject, and condition (6 con images set up as 1 main effect; I just like doing it as 1 factor and testing the interaction by using the appropriate contrast weights).
I get stuck in how to set up the pmod, give that it isn't present during the control conditions.
1) Do you specify the pmod condition as a separate factor?
2) How do you set up the conditions matrix when specifying the scans for each subject?
3) To test the effect of the pmod independent of any main effects, do I have to specify an interaction between task conditions and the pmod conditions?
Originally, I tried just making 1 main effect with 10 regressors, but then realized you can't set a contrast to test the effects of the pmod against 0, as the contrast weights have to sum to 0.
Any help would be greatly appreciated.
Many thanks,
Kris
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