Hi Darren,
> I think that the analysis I want to do in FSL is:
>
> Ca La Ma
> Ca - (La & Ma) 2 -1 -1
> La - (Ca & Ma) -1 2 -1
> Ma - (Ca & La) -1 -1 2
>
> because I am wanting to isolate the unique cognitive aspects that are
> attributable to the Ca condition and trying to remove the motor and
> sensory activations that are common to La and Ma.
>
> Three questions arise that I wish I had more confident answers to:
>
> 1. Does that look more sensible within the context of FSL and given
> what demeaning does?
>
> 2. Does this appear to be a reasonable replication of the AIR analysis
> I did previously given the conceptual differences in FSL? If not, what
> would be a better design that would approximate what I was doing with
> AIR?
Yes - I think this makes sense. You _might_ also want to include confound
regressors for the "question" periods, to take out the variance from these
events - the contrasts wouldn't use these EVs. Doing this might make
things better but not necessarily.
> 3. How would I use F-tests to further help illuminate these contrasts?
> How would I set the F-tests up? How would I interpret the resulting
> activations in volume created in the F-test?
Depends which other questions you might want to answer. For example, to
ask about any activation in CA/La/Ma just do an f-test on these 3; to ask
about your contrasts above but without insisting that they be positive,
just put an f-test on whichever one you are interested in.
Thanks, Steve
Stephen M. Smith MA DPhil CEng MIEE
Associate Director, FMRIB and Analysis Research Coordinator
Oxford University Centre for Functional MRI of the Brain
John Radcliffe Hospital, Headington, Oxford OX3 9DU, UK
+44 (0) 1865 222726 (fax 222717)
[log in to unmask] http://www.fmrib.ox.ac.uk/~steve
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