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> 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 > modulation. > 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