Dear Steve,
Thank you very much for your help. I have one more question....
The task consists of three sessions for each subject. The order of the 4
types of stimuli (ABCD) is different across the three runs. In running one
subject through FEAT, I selected a full first level analysis for 3 volumes,
and then selected one session for each volume. However, because the order of
the stimuli is different across the three sessions, I cannot tell FEAT what
the order is for each session, as I think it assumes that they are the same
for each session.
I have considered two approaches to this. Firstly, to set up and analyse
each session separately. Alternatively, to concatenate the three sessions
into one very large session, and analyse it that way. Is either of these
appropriate, or is there a better way?
Many thanks
Xavier
-----Original Message-----
From: FSL - FMRIB's Software Library [mailto:[log in to unmask]]On
Behalf Of Stephen Smith
Sent: 06 September 2001 17:23
To: [log in to unmask]
Subject: Re: [FSL] FEAT
Aha - good - so in fact all your scanning IS regular, and my initial
worries are gone.
So - to your original questions:
>>>>
I set up the analysis (for a single subject as follows). I selected a full
model setup. Given that there are 4 active conditions, I selected 4 EVs.
For the basic shape, I selected Custom (1 entry per volume). I then
created 4 text files, one for each of the active conditions. In each text
file, I used 1 to specify images relating to that active condition, and 0
for every other image.
>>>>
this is fine - though it might have been easier to simply specify the
activation periods (seconds) for each EV type in 3-column format text
files. the result should be the same.
>>>>
For the contrasts, I looked for activations in each of the active
conditions (by selecting 1, and 0 for all the others)
>>>>
this is fine too - and if you want to compare conditions, use [1 -1] type
contrasts.
Sorry for the confusion - hope it gives the activation you want!
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
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