I have a question about the reversibility of contrasts in an analysis. It makes sense that in most fMRI studies, for every A>B contrast, the "opposite" B>A contrast is usually also checked; this is, from what I understand, due to the voxel-wise nature of the stats, and to the necessary cross-voxel averaging, which makes the differences between two conditions not "symmetrical" and thus necessitating investigation from both "ends".
On the other hand, sometimes, for an A>B contrast, not only the positive t-values but also the negative ones are reported, with the implication that, if B is taken as a baseline condition, the brain areas produced by this contrast are "deactivated" – a term whose intuitive interpretation there seems to be disagreement on.
What I am wondering is whether doing the opposite contrast is the same as looking at both negative&positive t-values in the original contrast. In other words, are negative t-values for contrast B>A the same as positive t-values for contrast A>B?
-> If so, then why are some studies doing both?
-> If not, then what exactly is the difference between them, and which one is the correct one to use when examining both "sides" of a contrast?
Thanks for any help with this!
--Francesco