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Effect of A independent of P1 and P2 -  1 0 0 0 0 0 0 0 0
Effect of A modulated by P1 - 0 1 0 0 0 0 0 0 0
Effect of A modulated by P2 - 0 0 1 0 0 0 0 0 0

For modulation, you are testing the slope essentially, so the mean response doesn't matter. The effect of A is the mean response of the A.


Best Regards, Donald McLaren
=================
D.G. McLaren, Ph.D.
Postdoctoral Research Fellow, GRECC, Bedford VA
Research Fellow, Department of Neurology, Massachusetts General Hospital and Harvard Medical School
Office: (773) 406-2464
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On Mon, Mar 28, 2011 at 4:49 AM, megha sharda <[log in to unmask]> wrote:
Hello,

I was trying to make a design with parametric modulators in SPM5 and had some questions. 

I have 3 task conditions A, B and C and 2 modulators P1 and P2 which vary across different trials in all three conditions. So I have modelled a first level design with 3 primary conditions/regressors each with two parametric modulators giving me a design matrix with 9  columns for each of the regressors. 
Now I want to look at the effect of the conditions A, B and C independent of parametric modulators as well as effect of each of the conditions modulated by the regressors P1 and P2 independently. My question is, what should be the contrast at first level and 2nd level to look at these effects?

Are these correct-
Effect of A independent of P1 and P2 -  1 0 0 0 0 0 0 0 0
Effect of A modulated by P1 - 1 1 0 0 0 0 0 0 0 OR 0 1 0 0 0 0 0 0 0
Effect of A modulated by P2 - 1 0 1 0 0 0 0 0 0 OR 0 0 1 0 0 0 0 0 0

I would be very grateful for some help.

Thanks!
Megha

--
Megha Sharda
Graduate Student
National Brain Research Centre
Manesar, Gurgaon -122050
India
Ph: +919810943202