Dear SPM experts,
In my experiment, each subject performed 4 sessions of trials. In the 1st, 2nd, 3rd and 4th session, there is an EV entitled p1, p2, np1, and np2 by order. We want to know which brain region’s time course is associated with the time course of a seed region “ABC” in an interaction manner [i.e., (p2-p1) – (np2-np1)]. In other words, we have to establish PPI EVs for these 4 EVs. We execute the commands below (the same as my previous post) when matlab is in the directory of the 1st-level model folder which contains the SPM.mat file.
clear;
load SPM.mat;
P.subject='subject1';
P.directory=pwd;
P.VOI=[pwd filesep 'VOI_ABC.mat'];
P.contrast={'Omnibus F-test for PPI Analyses'};
P.Estimate=1;
P.extract='eig';
P.Tasks={'1' 'p1' 'p2' 'np1' 'np2'};
P.Weights=[];
P.analysis='psy';
P.method='cond';
P.CompContrasts=1;
P.Weighted=0;
P.Contrasts(1).name = ['ppi_p2-p1'];
P.Contrasts(1).STAT = ['T'];
P.Contrasts(1).left = {'p2'};
P.Contrasts(1).right = {'p1'};
P.Contrasts(1).Weighted = 0;
P.Contrasts(1).MinEvents = 1;
P.Contrasts(2).name = ['ppi_np2-np1'];
P.Contrasts(2).STAT = ['T'];
P.Contrasts(2).left = {'np2'};
P.Contrasts(2).right = {'np1'};
P.Contrasts(2).Weighted = 0;
P.Contrasts(2).MinEvents = 1;
P.Contrasts(3).name = ['ppi_(p2-p1)-(np2-np1)'];
P.Contrasts(3).STAT = ['T'];
P.Contrasts(3).left = {'p2' 'np1'};
P.Contrasts(3).right = {'p1' 'np2'};
P.Contrasts(3).Weighted = 0;
P.Contrasts(3).MinEvents = 1;
PPPI(P);
However, we failed because of the error message “p2 does not exist. Program will exit”. Can anyone help?
Thanks. Mike
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