Hi,
Based on prior discussion (i.e., the order of parametric modulators matter) and a study published in NeuroImage (Mùˆller-Pinzler et al., 2015), I would like to clarify my understanding and hope some experts could help. Suppose I have a regressor of interest, i.e., a decision process ("DEC"), as well as trial-by-trial attentional level ("ATT") and subjective difficulty level ("DIF"). I'm interested in the following activations:
(i) brain activations during DEC
(ii) brain activity modulated/explained by ATT
(iii) brain activity modulated/explained by DIF
Analysis 1:
(A). For (i), I construct a first-level GLM without any parametric regressor (PM) to identify decision-related regions.
(B). For (ii), I construct a separate first-level GLM, in which only one PM (i.e., ATT) of hemodynamic responses during the decision period is included. A contrast focusing on this PM is then set.
(C). For (iii), I construct a third first-level GLM, in which only one PM (i.e., DIF) is included. A contrast focusing on this PM is then set.
Analysis 2:
(A). Same as (A) in Analysis 1.
(B). For (ii), I construct a separate first-level GLM, in which the PMs contain first, the DIF and second, ATT. A contrast focusing on ATT is then set.
(C). For (iii), I construct a third first-level GLM, in which the PMs contain first, the ATT and second, DIF. A contrast focusing on DIF is then set.
So which one is correct?
Also, for decision-related regions, i.e. (i), should I report activations from the contrast focusing on DEC in (A), (B), or (C)?
I think Analysis 1 is ok but Analysis 2 is more specific and without mutual confounding of the two PMs (However, if I use Analysis 2, I won't be able to identify brain regions that are correlated to both ATT and DIF?). Also I think I should report decision-related regions identified in (A). But confirmation is needed
Thanls a lot.
Mike
|