Hi - I'm struggling to understand exactly your question, because I'm not
sure what your first-level analysis was - what EVs and contrasts did you
run at first level?
Thanks, Steve.
On Wed, 7 Jan 2004, Philipp Prahs wrote:
> Hi,
>
> I am trying to analyze a couple of measurements of 4 subjects who are
> measured under an active and a neutral condition repeatedly (4 times). After
> carrying out the first level analysis seperately I started a higher level
> analysis containing all 4 subjects. I set it up with 4 EVs (one for each
> subject) and ran the analysis for the "active" and "neutral" condition
> seperatly.
> EV1 EV2 EV3 EV4
> Subj1 1st Meas 1 0 0 0
> Subj1 2nd Meas 1 0 0 0
> Subj1 3rd Meas 1 0 0 0
> Subj1 4th Meas 1 0 0 0
> Subj2 1st Meas 0 1 0 0
> .
> .
> .
>
> Contrasts
> Subj1 1 0 0 0
> Subj2 0 1 0 0
> Subj3 0 0 1 0
> Subj4 0 0 0 1
>
> After that I ran an analysis using the cope images from the analysis above
> to get the group mean with one ev and all ones in the matrix
>
> My first question: Is it now legal to use the resulting cope images of the
> "active" and "neutral" conditions carried out similarly to get a contrast of
> "active" more than "neutral", like to EVs one for each cope image and a
> contrast with 1 -1 and -1 1 for both directions?
>
> My second question: When I try to get that contrast in a higher level
> analysis of only one measurement of one subject including only the "active"
> and the "neutral" measurement (2 datapoints) with 2 EVs 1 0 (active) and 0 1
> (neutral) with contrasts 1 0 (active only) 0 1 (neutral only) 1 -1 (active
> more than neutral) and -1 1 (neutral more than active) flame complains about
> the matrix being singular. Where did I make a mistake? I thought that this
> analysis should be possible.
>
> Thanks very much for any help with any of those questions.
>
> Philipp Prahs
> Dept. of Radiology - LMU Munich
>
Stephen M. Smith DPhil
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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