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