Dear SPM experts,
I have a question concerning interpretation of PPI analysis. In our experiment there are two long alternating conditions (regressors 2 and 4 shown in the design matrix). I performed analysis of interaction of the both conditions and the signal of a volume of interest, like described in the SPM manual for one and for the other condition separately.
The significant interactions where quite similar for those conditions. This seems surprising to me, because I expected interactions of two alternating conditions with physiological signal form VOI have different effects.
What must be the interpretation of those results? Maybe I have to modify the way I perform the analysis?
In fact I am interested only in the effect of only one condition, but it difficult to make any interpretation of shared effects at the moment.
Looking forward to any advice. Thank you in advance for your comments!
Sincerely yours,
Vladimir
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