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In my questions experiment, I have seven different explanatory
variables (categories of questions).  For each of the twenty eight
questions asked during a session, there are three volumes collected
(question being asked, answering, and rest (TR=4)).  I set up the
explanatory variables in FSL using the rest volumes.  Now, I am trying
to make sure I understand what I will be getting using different types
of contrasts.   In particular, I am trying to understand the
implications of demeaning in FSL.

One contrast I could look at is:

                A       C       L       M       R       T       U
A               1       0       0       0       0       0       0

 From my understanding, this gives me the mean activation under the A
condition, having already subtracted out the mean level of activation
during the entire experiment (ACLMRTU x qar)


Another contrast would be:

                A       C       L       M       R       T       U
A               6       -1      -1      -1      -1      -1      -1

My best guess of this contrast is that it is going to show me the
activations for A that are distinct from activations that are happening
in CLMRTU.

So, I think that the first contrast would show activations like the
finger press or the auditory activations.  And, I guess I would expect
that all seven conditions would look pretty similar since I would
expect the obvious motor or sensory activations to obscure the more
subtle cognitive differences.  And, I would assume that the second
contrast would take out the common motor and sensory activations and
highlight the cognitive differences particular to condition A.  Is that
correct?

Further more, how would I use the F test in this case.  I am familiar
with the meaning of F tests when I use them to evaluate whether the
differences between to subject populations are statistically
significant.  But, I am not clear on the meaning of the maps generated
by using an F test in FSL.

Thanks in advance,

        Darren