Dear SPM experts,
I have a question addressing time and dispersion derivates in T- and F-Contrasts in the 1st level analysis.
Assuming, having the following GLM:
FamousFaces(HRF); FamousFaces(TimeDerivate); FamousFaces(DispersionDerivates); NonFamousFaces(HRF); NonFamousFaces(TimeDerivate); NonFamousFaces(DispersionDerivates); 6xMotionParameters
So far I understood that if I include the time and dispersion derivates in my GLM, i have to use an F-test (e.g. [eye(3),eye(3)*-1] for differences between FamousFaces and NonFamousFaces), but these F-tests are not directional.
For a directional statement (e.g. more “activated” in FamousFaces than NonFamousFaces), I would use a T-test in the same GLM (e.g. 1 0 0 -1 0 0).
My question now is if this is correct, because I'm assuming that in this contrast, the time and dispersion derivates act as nuisance parameters, which are “correcting” for time and dispersion of the HRF.
Is this assumption correct?
So, would it be better to do a new GLM without time and dispersion derivates, or is there a method to combine the HRF, the time derivate and the dispersion derivate and perform a directional test?
University of Basel