Hi,

I am trying to conduct a trial by trial analysis using 3dDeconvolve's -stim_times_IM option (to generate separate beta estimates for each trial in each condition). As a sanity check, I'm having 3dDeconvolve calculate an all vs. baseline contrast using the glt option (shown at the bottom of this post). The script completes without error, but results in strange values for this contrast for only some runs. One run will have coefficient values ranging no more than about +/- 100, but the next run will have all values more extreme than +/- 10^8 (so that even thresholding at the most extreme value does not block out any voxels). However, this does not happen for the beta estimates for the trials themselves, only the contrast. I'm wondering what might be causing these improbably extreme values. Any advice? Maybe this is not ultimately a problem because it's just an issue with the sanity check?

If it's relevant, the onsets of each trial do not coincide with the onset of TRs. The duration I'm modeling always starts 200 ms before the TR and lasts until halfway through the TR (1000 ms). So one condition's line is:

-stim_times_IM 1 subject_cond1.1D 'GAM(8.6,.547,1.2)' -stim_label 1 cond1 \

where I'm explicitly setting the duration of the gamma as 1.2 seconds. Could this be causing the issue?

To create all vs. baseline:
-num_glt 1 \
-glt_label 1 allVSfix \
-gltsym "SYM: +cond1 +cond2 +cond3 +cond4 -4*Ort[0]"

Thank you for your help!
Ben