Hi,
> Based on the above, however, I have few questions:
> 1) Regarding Marsbar: I expected Marsbar timecourse to take into account
> (and remove the effect of) global brain signal since this was scaling
> applied in the analysis. I selected the option to include scaling from
> spm.mat during Marsbar calculation. Is anyone familiar with why this has not
> happened or is there another explanation?
There are several forms of scaling in SPM (and therefore MarsBaR).
Some scalings are applied to the images themselves, before they enter
the analysis - for example session-specific mean scaling, or
proportional scaling. These forms of scaling will be reflected in the
image information in the SPM.mat file.
The ANCOVA scaling is different, because it is applied as regressors
in the design matrix. This means that you won't see the effect of
ANCOVA unless you are using the design matrix and its estimated
parameters to remove the effect of the globals on the time course. To
do this, you will need to use the SPM / MarsBaR results interface to
show fitted and adjusted data for your effects of interest. In this
case the effects not of interest have been removed, including the
estimated effects of the global signal.
Best,
Matthew
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