Per McLaren et al. in Neuroimage in 2012, you should produce 6 PPI regressors and the 6 original EVs. You also include the physiological regressor. This will lead to 13 EVs. Then you can form the contrast of the difference of the 2EVs and use those for the higher level models.

Hope this helps.

Best Regards, Donald McLaren
=================
D.G. McLaren, Ph.D.
Research Fellow, Department of Neurology, Massachusetts General Hospital and
Harvard Medical School
Postdoctoral Research Fellow, GRECC, Bedford VA
Website: http://www.martinos.org/~mclaren
Office: (773) 406-2464
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On Sun, May 3, 2015 at 11:13 AM, Jie Yu <[log in to unmask]> wrote:

Dear Expert

I now have 6 EVs.

I am only interested in PPI of 2EVs.

Do I have to produce new PPI regressors for each of these 6 EVs?

So that each of the 6 original EVs will have its individual PPI regressors (original EV * physiological regressor of the ROI)?

Overally I will have 13 EVs? (6 original EVs + 1 physiological regresssor + 6 PPI regressors)

Thanks!