Hi,
sorry if anything remains unclear here - my knowledge of neither fsl nor
english is very advanced.
At first level I used only one EV and one contrast ("1") according to
our paradigm (40 seconds rest,
16 second active or neutral stimulation, repeated 3 times). I ran the first
level analysis seperately for "active" and "neutral" conditions. Are you
suggesting that I could
run a first level analysis including both "active" and "neutral"
conditions with 2 EVs and contrasts
"1 0", "0 1", "1 -1" and "-1 1". I did not think of that in the first
place because I have seperate files
containing "active" and "neutral" conditions. But I think it should be
possible to merge them with avwmerge.
Thanks very much for any comments or suggestions.
Philipp
Stephen Smith wrote:
>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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