Dear Paymon,
Do you have any specific reason to choose a different "canonical" HRF
for each group? I understand that there are age-related HRF changes,
but I wasn't aware that these were systematic enough to justify a
specific choice for an old-age HRF. I would thought that choosing a
double gamma function for both groups would offer you the best
overall fit in the absence of any other information.
If you do choose different HRFs, you will almost certainly need to
demonstrate some empirical basis for your choice because otherwise
any group differences could simply be the result of differences in
the quality of fit based on the HRFs chosen...
Just my $.02
- Joe
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Joseph T. Devlin, Ph. D.
FMRIB Centre, Dept. of Clinical Neurology
University of Oxford
Headley Way
Oxford OX9 3DU
Phone: +44-(0)1865-222-494
Email: [log in to unmask]
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