hello Jill and PPI experts,
We have been running series of PPI analyses in FSL following the useful
guidelines on Jill O'Reilly's webpage.
However, we have noticed a couple of quirks with the PPI output vs. the
default FEAT 1st Level output. That is, the inclusion of the Physiological
Regressor (PHYS) and PPI in the EVs will change the observed output of the
"Psychological" statistical maps (the EV of interest) compared to the output
produced in the default FEAT analysis.
We had assumed that the inclusion of the Physiological Regressor (PHYS) and
PPI Intercation EV would make no difference to the modeling of the
"Psychological" EVs of interest. But it does!
So does this difference matter and does it impact on the PPI output map?
Finally, as a shortcut we were trying to include multiple Physiological
Regressor (PHYS) and PPI's in a 1st level analysis (ie trying to model > 2
PPI's int he same analysis) and that produces very different output maps
compared to running only one PPI in the analysis.
Any thoughts or suggestions?
cheers,
Marc
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