Your test for the quadratic effect is correct. Best Regards, Donald McLaren, PhD On Fri, Sep 25, 2015 at 3:21 PM, Joelle Zimmermann < [log in to unmask]> wrote: > Hi SPMers, > > I'd want to learn how to set up a quadratic parametric modulator. I've > inputted my parametric modulator on the first level model, selected > second-order, and now I get an additional column in my design matrix (as > opposed to if I did a first-order linear parametric modulator - then I > would get only one column corresponding to the PM). > > So my first column is my task design, and next two columns are my PM. I'm > assuming that the second column corresponds to the linear aspect of my PM, > and the third column to the quadratic aspect of my PM? > > So if I'm interested purely in quadratic effects, can I put a contrast > over the third column only, such as: > [0 0 1] > > or, should I always also test for linear effects when interested in > quadratic effects. But Im not sure how I would set up that contrast. > > Thanks, > Joelle >