Hi,
While doing gPPI, the optional field "contrast" says:
"Contrast to adjust for. Adjustments remove the effect of the null space of the contrast. Set to 0 for no adjustment. Set to a number, if you know the contrast number. Set to a contrast name, if you know the name. The default is: 'Omnibus F-test for PPI Analyses'."
In the "5. Tutorials" section, both traditional PPI and gPPI used P.contrast=0.
Should I use 0 or default? If I used default, it removes the effect of the null space of the contrast across all conditions--- just like what happens when I extract eigenvariate time series in a VOI, right?
Thanks.
Mark
|