In using gPPI for traditional PPI analysis, the columns are not easily labelled and the task names are not included in the design because there are no task columns.

To automatically generate the contrasts. You need to set P.Contrasts.left=[0 1 0 0] and P.Contrasts.right=[];

This assumes 1 run, no motion parameters. You basically need to setup the contrast by hand where you put a 1 over each PPI column and then feed it to the program.

Unfortunately, there isn't a more automated approach. I'm working on a way to only have to specify the contrast for the first session, but it might take a bit of time to incorporate.

Let me know if you need a clearer explanation.

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 Tue, Nov 8, 2011 at 2:05 PM, Bob Spunt <[log in to unmask]> wrote:

I am using the excellent gPPI toolbox (http://www.brainmap.wisc.edu/PPI) to run PPI in SPM. For the purposes of comparison to the generalized (condition-specific) approach, I am using the toolbox to run the traditional (A-B) approach to PPI. All runs well, except I cannot figure out how to make the toolbox compute the contrast for the PPI regressor. I have P.CompContrasts set to 1, and I have tried setting the P.Contrasts field to either:

P.Contrasts(1).left = {'PPI'}   % this is the name given the regressor by the script

P.Contrasts(1).right = {''}

or

P.Contrasts(1).left = {'A'}      

P.Contrasts(1).right = {'B'}

% where in this case my PSY term is formed from the [1 -1] weighting of conditions A - B

Any tips on why the contrast for the PPI regressor is not automatically computed? 

Many thanks in advance,

Bob

-------------------------------------------------------------------------------

Bob Spunt
Postdoctoral Fellow

Social Cognitive Neuroscience Lab - www.scn.ucla.edu
Department of Psychology
University of California, Los Angeles