Dear FSL Users,
I have a decent amount of experience with FEAT, but have never used it to
perform group comparisons and would like some clarification on setting up
the EVs.
We have a data set with 20 subjects: 10 control and 10 concussed
individuals. Each subject completed a number of different tasks, but with
only 1 run per task. Originally I thought the correct way to perform a group
comparison was to first estiamte the activation for each of the groups and
then contrast the 2 resulting .gfeat directories (similar to what is done is
SPM). Apparently this either doesn't work in FSL or I am setting it up
incorrectly, as I do not end up with any cope directories.
Going through the FEAT manual, it seems the setup provided for the Two
Sample unpaired T-test (which is a 2nd level analysis, not a 3rd as I
originally thought I would need) is the most similar to what I need. But I
have a few questions about this.
1. Is it possible to do the group contrasts as I had originally performed
them? If so, are there any disadvantages to this?
2. I don't quite understand why the setup for the unpaired has 2 EVs which
seem to specify which group the subjects belong to, when there is already a
Group column which specifies just that.
3. Concerning the above, how do the Group and EV variables interact?
I apologize if these questions seem rudimentary, but I guess my previous
experience with SPM is preventing me from understanding the FSL method.
Thanks,
Carlos
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