> Dear SPMers,
> After unsuccessfully searching the archives and the net I would very
> much appreciate your help on the following:
> I want to identify which regions of the brain show an activation
> pattern that follows 1) linear and 2) a quadratic trend with the
> increasing task load.
> I have 4 levels of load and was going to define the matrix with 1
> condition (all onsets of all 4 loads) with a categorical parametric
> My questions are:
> 1) how should I enter the parametric modulation vector? Would 1,2,3,4
> for the 4 loads be correct or should I orthogonize this and enter -1.5
> -0.5 0.5 1.5(for linear) and 1 -1 -1 1 (for quadratic) instead?
> 2) should I specify 2 parametric modulations (with identical vectors)
> one being described as linear and the other as quadratic in order to
> tease apart regions that may follow different trends ?
> 3) finally, when defining the contrast, should I specify 0 1 0 if I
> want to visualize the regions with the linear trend and 0 0 1 with
> quadratic trend (the 1st regressor beeing the condition)?
> Thank you very much, any help will be very much appreciated.
> Olga Prilipko