Dear SPM users,
I am currently analyzing a complex event-related MRI-design. In brief, we acquired 6 functional runs of 10 minutes each using a TR of 1s. Moreover, since we are interested in investigating the chronometry of the BOLD-signal in several ROI's, we want to apply a FIR-model to the data.
Initially, after modeling all regressors (cues, stimuli, ratings etc.) that needed to be convolved with a BOLD-response, we ended up with 72 regressors * 6 sessions = 432 different regressors. For the MRI-model specification we implemented a FIR basis set with a window length of 30 seconds and 30 basis functions (1 p/s). The window length might seem overdone, but our longest (painful) stimulation is 16 seconds and we want to be sure that we model the full scope of the BOLD-response until it returns to baseline. This approach yielded a total of 12960! different beta-images, raising several types of memory problems in Matlab. We could probably have worked towards a solution, but in the end we decided to just concatenate all regressors of relatively little interest into a general regressor called 'Everything else', and to keep the 16 most important regressors as they are, leaving a more workable 3060 beta-images. Using this approach we are now able to run the model estimation succesfully (something we had problems with before). However, now we are running into problems with the contrast manager.
Even when specifying a simply contrast e.g. setting the weight of the first 30 beta-images corresponding to the first condition regressor to one, and the weight of the next 30 beta-images corresponding to the second condition regressor to minus one (replicating over sessions), the contrast fails. I have tried several solutions, including downscaling the relative weight of the regressors, however, none worked. I am wondering whether anyone would have a clue of what might be causing the problem?
The contrast manager crashes without to much mention of what is exactly going on. However Matlab is providing some clues. This is the main error message:
Failed 'Contrast Manager'
Error using spm_run_con (line 249)
Error in contrast specification
In file "/home/jellezorn/programs/SPM/spm12/config/spm_run_con.m" (v6764), function "spm_run_con" at line 249.
Ant this is the part in the script that is giving an error:
%-Basic checking of contrast
%------------------------------------------------------------------
[c,I,emsg,imsg] = spm_conman('ParseCon',cons{k},SPM.xX.xKXs,STAT);
if ~isempty(emsg)
disp(emsg);
error('Error in contrast specification');
else
%disp(imsg);
end
Any feedback would be much appreciated.
Thanks a lot in advance.
Kind regards,
Jelle
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