Hi all (and especially Gang ,

I know this has been discussed before, and there were also some notes about it on Gang's page (which do not seem to exist anymore), but I wonder what is the current preferred method in afni land for detecting regions that are significantly activated by two contrasts --- (cond.A - cond.B) and (cond.C - cond.D) --- and whose levels of activation are *not* significantly different from one another --- i.e. (cond.A - cond.B) is *not* significantly different from (cond.C - cond.D). I remember a while ago the standard procedure was to create a simple intersection map of two already thresholded and clustered maps, but that does not answer exactly the same question. Would it make sense to further multiply this intersection map by the brain-wise complement mask of the thresholded and clustered map for the contrast [(cond.A - cond.B) - (cond.C - cond.D)] (that is, the mask of non-significant voxels for the latter contrast)?

Also, what would be a sensible choice for the threshold of the maps to be intersected? Is there any principled ground for it to be less stringent than when assessing a single contrast?

thanks for any comment
giuseppe