Hello,

Your suspicion is probably correct: the t-statistic is something like the difference between two sample means, scaled by their standard error (and there are several ways to estimate the standard error).

But without knowing the software program and the t-statistic you are referring to ("the mean of T value and the number into the parenthesis"), I cannot be sure it is the correct interpretation for your results. It could be that you are seeing the average t-statistic for a region of interest (and the associated measure of variability among the t values). Examining the basic descriptive statistics between your groups may be helpful.

Some more information can be found here:
T-statistic in general:
https://en.wikipedia.org/wiki/Student%27...

T-statistic as contrast in neuroimaging:
http://mindhive.mit.edu/node/60f

Steve
---
Steve Hodge