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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

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