Convolving block task timing with Double-Gamma HRF

AFNI Message Board
1

Hi all,

How would one go about convolving the block task timing for a breathhold task in 3dDeconvolve with FSL’s Double-Gamma HRF with temporal derivative and temporal filtering? I’m conducting separate analyses in AFNI and FSL, and I want to ensure the models are fairly similar. Also, does AFNI’s block function in 3dDeconvolve significantly differ from this?

Thanks,
Alain

2

Use the basis function ‘SPMG2’ in 3dDeconvolve.

3

Great! Would I simply replace Block(15,1) with SPMG2 in the following script?

3dDeconvolve -input 101.breathhold.BOLD.nophymotcorr.tcat.scale.nii
-polort 2
-num_stimts 1
-stim_times 1 breathhold_stimulus.1D ‘BLOCK(15,1)’
-stim_label 1 breathhold
-iresp 1 BH_test.101
-jobs 2
-fout -tout -rout -bout -x1D X_test.xmat.1D -xjpeg X_test.jpg
-fitts fitts_test.101
-errts errts_test.101
-bucket stats_test.101

4

Would I simply replace Block(15,1) with SPMG2 in the following script?

Use SPMG2(15).

5

Thanks! When using this function, what is the most appropriate way to incorporate the breathhold delay? The literature using AFNI for breathhold analyses often uses terms like “the block regressor delayed by 9 s”. Do I simply add 9 s (or whatever the chosen lag) to each stimulus onset time in the stimulus timing file, as I had done before?

6

Do I simply add 9 s (or whatever the chosen lag) to each stimulus onset time in the stimulus timing file, as I had done before?

Yes, that should work.