Dear Colin,
Thank you. So, if I have two parametric modulators (pm) A and B and I want to know (1) brain activity modulated by A while regressing out the effect of B, and (2) brain activity modulated by B while regressing out the effect of A, I have to construct two first level models, with the first using B as the first pm and A the second for (1), and another one with reverse order for (2), right?
Also, I wonder about the term "regressing out." This is usually use in multiple linear regression, when we have more than two covariates, and their order doesn't matter. I'm not sure if this term is appropriate for parametric modulation in which the order matters.
Mike
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