Do you mean you want abs(subj1-matched1)? There's no parametric way to test a hypothesis based on this, but if you want it you can run

mri_concat --abs paireddiff.mgh abspaireddiff.mgh

doug

Mayuresh wrote:

Hi Doug, Nick and other freesurfer users,

I have two groups and each group has a matched pair of subjects. I am keen on identifying cortical areas where the difference between the matched pair in group1 is greater than that in group2. How can I do this in freesurfer?

...

From the email archive it seems to me that -paired-diff option with mris_preproc should do the trick, however as I understand this will create difference maps such that subject1-matchedsubject2. For my purpose I would be needing the absolute difference between the pairs. How can I acheive this?

Thanks for any pointers, Mayuresh

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