Dear Hendrik
As Donald mentions, when you know what you favorit hrf should look like you will need to modify some functions. There is a few ways to do this either by changing the way spm_get_bf calls spm_hrf, or this one which I prefer. I have added a field:
defaults.stats.fmri.hrfpar = [6 16 1 1 6 0 32];
in spm_deaults, although this file should not be edited! :-) But i hope the hack will make in the next release. Next I have changed the way spm_hrf finds its default values, namely using:
p = spm_get_defaults('stats.fmri.hrfpar');
instead of:
p = [6 16 1 1 6 0 32];
You can now change the default hrf to any other mixture of two gamma functions before you specify your fMRI design, e.g. an earlier peak with no poststimulus undershoot:
spm_get_defaults('stats.fmri.hrfpar', [4 16 1 1 inf 0 32])
You can either implement these changes, or replace your files with the ones attached.
Hope this helps
Best
Torben
Torben Ellegaard Lund
Associate Professor, PhD
Center of Functionally Integrative Neuroscience (CFIN)
Aarhus University
Aarhus University Hospital
Building 10G, 5th floor, room 31
Noerrebrogade 44
8000 Aarhus C
Denmark
Phone: +45 7846 4380
Fax: +45 7846 4400
http://www.cfin.au.dk[log in to unmask]
