I would like to use a custom hemodynamic response function for the GLM.

Therefore I replaced the variable ‘hrf’ in the spm_hrf.m file with my function, sampled over 20 seconds and a resolution of 1 second which corresponds to my TR. See the last two lines in the attached file. I made no further changes.

However, when I specify a 1st-level model, the design matrix turns out to be just a uniform grey color.

My guess is that something about the amplitude or duration of my function is wrong, do you have any suggestions?

Could it be that the file spm_Gpdf.m needs to be changed as well, even though I think it should no longer be needed for my hrf.


Plan B, manually convoluting a boxcar function with this hrf in matlab and entering it as regressor in spm works perfectly but that is quite tedious.


Thank you very much.





Felix Schlegel

Institute for Biomedical Engineering :: University and ETH Zurich

HIT E22.1, Wolfgang-Pauli-Str. 27, 8093 Zurich, Switzerland

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