Dear Joe,
> We are trying to understand the flow of information in
> creating the SPM(t) values.
> In several locations in our SPM(t) maps there were nonzero
> values which in the corresponding con_.img and ResMS.img
> files had NaN values,which was unexpected.
> Are these SPM(t) values linked to the individual images that
> were used in the group analysis in some way other than the
> con_.img and ResMs.img files ?
The SPM{t} of a contrast is comnputed by the same function as is the
con_*.img. Basically, this function looks at each voxel that entered the
parameter estimation and computes the contrast and the SPM{t}. The
mask.img of the analysis indicates, for which voxels parameters were
estimated. This means, if a voxel in the mask.img is zero, the con_*.img
should have a NaN-value there and the SPM{t} a zero. This could be
checked with the 'check reg' facility. Could you also check, whether
your con_.img and SPM{t} were generated by the same process? One
indicator would be the write time of the con*.img and SPM{t}. Or can you
repeat the process and check, whether you observe this strange behaviour
again?
Stefan
--
Stefan Kiebel
Functional Imaging Laboratory
Wellcome Dept. of Cognitive Neurology
12 Queen Square
WC1N 3BG London, UK
Tel.: +44-(0)20-7833-7478
FAX : -7813-1420
email: [log in to unmask]
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