Re: [Marsbar-users] signal intensity plots

[Matthew B. <mat...@gm...>]

Hi,

> When plotting the extracted data from an ROI (this is under the Data menu, option Plot Data (simple), NOT in the Results menu, option Marsbar SPM Graph) I get a plot of signal intensity across the timecourse of my experiment. Are these values adjusted in any way, eg, for global flow?

Yes - the SPM scaling has been applied, if you got these images via
the SPM design.  The adjustment for FMRI data is very simple, and
merely normalizes the grand mean signal across the brain (see
http://imaging.mrc-cbu.cam.ac.uk/imaging/PrinciplesStatistics#global_signal
and
http://imaging.mrc-cbu.cam.ac.uk/imaging/PrinciplesStatistics#grand_mean)
 to be 100 for each session.

> Also, once I've saved this plot and am working with the resultant *_mdata.mat file, what are the values stored in "y" and "Yvar" in the workspace? It seems logical that Yvar would be variance, but the values are too high to make sense. I'm having a hard time reconciling these files of similar names to those produced when using the Marsbar SPM Graph option (Results menu).

y is the data summarized for the ROI - usually the mean signal across
the ROI therefore.  Yvar is the variance across the ROI,

Best,

Matthew