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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
>