Hello,
I have been running some analyses and I have some questions about F-tests
and contrasts.
When running FEAT on individual subjects in first-level analysis, clicking
on the stats tab, and selecting the Full-model setup, there is a section
for setting up F-tests and contrasts.
In my experiement I have 3 tasks of interests, i.e., 3 EV's in my GLM model.
So I set up my contrasts and F-tests as such:
EV1 EV2 EV3 F1 F2 F3
OC1 * 1 0 0 * 0 0
OC2 * 0 1 0 0 * 0
OC3 * 1 0 0 0 0 *
(* indicating yellow clicked box)
The trouble I'm finding is that when I look at the resulting activation
maps for zstat and zfstat maps, I see two completely different pictures. I
don't understand why. For the zstat activation map, I barely see any
activation, but for the zfstat activation I see several clusters of voxels
in ROI's we typically see from our experiments. Is there something I'm
doing wrong? Then when I take the individuatl subjects and make a group map
of a one-sample t-test and I include and F-test with it, I get the same
picture:
hardly any activation in the zstat group map, but I do see activation in
the several ROI's in the zfstat map.
What is going on? I would think I would see the same, if not similar
results. Is there something wrong with my contrast and F-test set-up at the
first-level analysis?
Your help would greatly be appreciated
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