Hi,
On Mon, Apr 18, 2011 at 11:31 PM, Elsa Baena <[log in to unmask]> wrote:
> Dear SPMers,
>
> I would like to extract effect sizes for functional ROIs across multiple subjects for an event-related design, using MarsBar. The way I understand this is done in MarsBar is the following:
>
> 1) Extract ROI data (Select ROI and SPM file)
> 2) SPM graphics window will open an input summary
> 3) Save the data to a file
> 4) In MatLab, open the saved file in workspace, open Y matrix.
>
> If I understand correctly, the Y matrix is a table of effect sizes for each of my subjects for the selected ROI. Is this correct or are the values in the Y matrix percent signal change?
>
> Additionally, what values compose the Y var matrix?
>
> Any help will be greatly appreciated.
I think you want the marsbar list for this one.
The procedure above extracts the raw (unmodeled) data in the images in
the SPM.mat. If the SPM.mat is a first level model, then, for an FMRI
design, this gives you the mean of the raw FMRI time courses within
your ROI. Yvar is just the variance across voxels at each time point.
If you loaded an SPM.mat for a second level model, then your images
will be say contrast images, and the ROI values will be contrast
values.
To get percent signal change you would have to go through the percent
signal change menu, or use the signal change batch.
Does that answer your question?
Best,
Matthew
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