Dear FSL experts,
I have a few questions regarding the analysis of event-related fMRI. FSL
is quite new to me and I'm trying to get my head around a few things!
In my study there were 16 subjects who were scanned on 2 separate days. On
day 1 they performed a cognitive task at baseline and again following the
administration of a placebo or drug, and on day 2 this was repeated, such
that each subject performed the task 4 times: at baseline ('BP') then
placebo ('P') and at baseline ('BD') then drug ('D'). The task consisted
of 2 event types A and B, and reaction times (RTs) were obtained for each
event.
Firstly, I would like to use RT as a covariate. My questions are the
following:
1. Can I combine the 2 different event types with their corresponding RTs
in the same analysis or do they have to be analysed separately? i.e. will
I need to analyse event type A for each subject and feed these feat
directories into higher level analysis and repeat this for event type B?
2. Will I need to analyse the sessions (BP, P, BD and D) separately or can
each individual and each session be put into the same higher level
analysis with RT as a covariate?
3. I'm unclear as to what people mean by demeaning covariates, please can
you explain?!
4. I'm also not sure whether it would be appropriate to tick the
orthogonalise boxes?
I'd also like to look at the mean group BOLD responses in the 4 different
conditions, and compare between them (e.g. D versus BD, D versus P).
1. Again, can I combine the 2 different event types in the same analysis
or do they have to be analysed separately?
2. Which is the best approach to do this, to put all data (each subject
and each session) into a one factor 4 level repeated measures ANOVA?
A couple of other things, do the post-stats set at the individual subject
level affect stats done at higher levels? Also, I'm confused about what
the difference is between inputting feat directories or cope images into
higher level analysis.
Many thanks!
Carolyn
