Dear SPM Experts,

I am trying to run a 2-sample ttests (2 groups, placebo and drug, each 
29 Subjects) and keep getting the error message 'there are no 
significant voxels' during model estimation. Running a one sample ttest 
with all those subjects in one group works fine.

The 2-sample script does run, if a specific subject is excluded. But 
most strangely, if this subject is kept in the group, but another 
subject is excluded, the script still runs fine. This is very strange, 
since the problem does not seem to be depending on one specific subject.

It is also the case, that the script only crashes for a few contrasts, 
estimating other contrasts defined from the same GLM works fine.


There have been a few suggestions on the mailing list, including the 
possibility, that the single subject contrast images (1st level 
analysis) do not overlap. But how could I check this?

Annother suggestion has been made that there is simply not a single 
significant voxel for the between group comparison for this contrast. 
But if this is the case, which threshold does SPM use to define a voxel 
as significant? Is it for example, that all the error message 'no 
significant voxels' occurs if no voxel has a p - vale < 0.05?

Do you know of any other reasons the script does not run?


Any help would be highly appreciated!

Thank you,

Stefanie

-- 
Dipl. Psych. Stefanie Beck
Technische Universitaet Dresden,
Faculty for Mathematic and Natural Science
Department of Psychology, Professorship for General Psychology
Zellescher Weg 17, 01062 Dresden, Germany

Office         Zellescher Weg 17, BZW, Room 324
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