[Freesurfer] cache.th13.neg.sig.cluster.mgh directionality

Hello,

I apologize if the questions are trivial- I have checked the archives, but could not find anything on this.

I have run a t-test between two groups on cortical thickness, and used mri_glmfit-sim for pos, neg, and abs versions.

1. If my FSGD is organized as: Group 1 Group 2

and my matrix file is 1 -1

Would a blue result in an absolute version indicate that Group 1 < Group 2?

2. When running the command: "less" on "cache.th13.pos.sig.cluster.mgh", I am getting 1 significant cluster, however, when running the same command on the "absolute" version of this file, there is nothing significant. Do you know why this might be the case?

Much appreciated,

Arkadiy