Hello SPM experts,
I have a basic question about how to interpret the output of the F vs. T contrast of a 2nd level analysis two-sample t-test. My design is straight forward. I have 2 groups (1st 2 columns of matrix), I included age a covariate (last 2 columns of matrix) and my contrasts are set up as follows:
0 0 1 0
0 0 0 1
0 0 1 -1 (group 1>group2)
0 0 -1 1 (group 2>group1)
My output always has many voxel clusters that have significant F values even with FDR correction. Since the F contrast is detecting bi-directional group differences in the voxels, I assumed that when I apply the T contrast, the specific directional differences would be extracted out in the relevant t-contrast set up. However, no signficant voxels are detected with either of the t contrasts.
Is my assumption incorrect? Does the F contrast significant results actually telling me anything meaningful? Thanks so much for any input!!!!