Hi - good question. The reason is that by default, tsplot produces these
mean timecourses from the data using weighting by the zstat images (within
the mask chosen). Hence the difference contrasts get different mean
timeseries as they have different weighting functions.
If you want to change this (ie turn off this within-mask weighting), edit
$FSLDIR/bin/featquery and change the call to tsplot to include the "-n"
optoin.
Cheers, Steve.
On Sun, 12 Jun 2005, Henry Lütcke wrote:
> Dear FSL Experts,
>
> I have performed featquery in order to get the signal time course
> averaged across all voxels in a region-of-interest. I guess this should
> be the first column in any tsplotc_zstat*.txt file in the
> featquery\tsplot directory. I find different values in the first column
> of the respective file for each of the five contrasts I have performed.
> Should the mean signal time course not be the same for all contrasts,
> since I am looking at the data for all voxels in a ROI?
>
> Thanks a lot for your help.
>
> Henry Lütcke
>
>
>
>
--
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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