Hi Tracy,
> I'm trying to conduct a second-level analysis of multiple sessions
> from a single subject, and I need some assistance. I have performed
> first-level analyses on each session. I have 10 sessions, and they do
> NOT have the same EVs/constrasts. For example, session 1 has 5 EVs,
> and session 2 has 6 EVs. In the second level analysis, I need to
> compare, for example, Right Cues (session 1, EV1) and Left Cues
> (Session 2, EV3), both Right Cue > Left Cue and Left Cue > Right Cue.
>
> Here are my questions:
> How do I specify fixed effects (or is that what I need)?
If you are doing Right vs Left for just one session vs another then yes
this has to be a fixed-effects analysis as that's not enough data to
estimate the (inter-session) mixed-effects variance. It is fairly unusual
to want to do this in isolation (ie when you are not then wanting to feed
this up for example into a cross-subject analysis, in which case you would
have the right vs left as part of a higher-level FEAT analysis) but I can
send you the simple command-line calls necessary to do this if you need
to.
Wrt having different numbers of EVs in the difference sessions first-level
anlayses, this is in general ok as long as the contrasts mean the right
things in the different sessions - this looks ok for you - you would just
change the "Inputs are lower-level FEAT directories" to "Inputs are cope
images".
Thanks, Steve.
Stephen M. Smith
Head of Image Analysis, FMRIB
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
|