Dear Fred,
At 18:11 13/05/99 +0200, you wrote:
| we are just evaluating an fmri experiement and it would
| be convenient for us to read the coordinates and the z values
| directly from the spmt.mat files. we realized that the numbers
| for the coordinates in the file do not directly correspond to
| the talairach coordinates in mm. does anyone know the conversion?
In SPM94-97 statistical resuls are saved only for voxels where the F-test
for "effects of interest" was significant. (Smoothness estimation was
performed on the entire volume for which all scans had data above the
"analysis threshold".)
The XYZ.mat file contains a single 3xK matrix, XYZ, which contains the
[x;y;z] co-ordinates in mm of the N voxels retained. If you have spatially
normalised the data prior to statistical analysis, these will be
"Talairach" coordinates insomuch as the normalisation templates are
regarded as being in Talairach space.
The SPMt contains a MxN vecor, SPMt, each row containing the Gaussianised
t-statistic (which will have a Normal distribution under the null
hypothesis) for the N voxels retained. Here, M is the number of contrasts
entered in the stats setup.
----------------
SPM99 saves statistical results for the entire volume as (floating point)
images - a lot more accessible and flexible. (Only the voxels at which raw
data is saved for plotting are selected by the default F-test for "effects
of interest".)
-andrew
+- Dr Andrew Holmes ------------------ mailto:[log in to unmask] -+
| ___ __ ___ Robertson Centre for Biostatistics |
| ( ,) / _)( ,) Boyd Orr Building, |
| ) \( (_ ) ,\ University Avenue, |
| (_)\_)\__)(___/ Glasgow. G12 8QQ Scotland, UK. |
+----------------------------------------- http://www.rcb.gla.ac.uk/ -+
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
|