Re: [Marsbar-users] Q regarding Extract Roi (Full Options)

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

Hi,

On Tue, Apr 24, 2012 at 7:47 AM, Andrew Furman <afu...@jh...> wrote:
> Hey All,
> A couple of questions regarding some of the options/functions of Extract Roi(Full Options)...
>
> 1. Is it appropriate to use this function directly on the .con files generated after running your GLM (assuming that you choose not to specify a SPM.mat)?

Yes, although it would be odd to specify things like global scaling.

> 2. What is the nature of the value generated when you select raw data? That is, what does the value represent with respect to the contrast I have selected. A colleague of mine suggested that it was derived from the Betas in the selected .con, but I am not so sure. Anyone have any ideas?

You mean - what numbers are in the contrast image?  They are linear
combinations of the betas.  If you had a design matrix with 2
conditions, and the first two columns were an HRF regressor for
condition 1 and condition 2, and your contrast was [-1 1 0 0 ... ],
then the resulting contrast image is an image of the beta_0002.nii -
beta_0001.nii .

Best,

Matthew