J Letting HRF shape varies allows for
subject and regional variability in
hemodynamics
J Can test HRF estimate for different
shapes; e.g., are later time points more
ÒactiveÓ than earlier?
L Need to estimate more parameters for
each stimulus class than a
fixed-shape model (e.g., 4-15 vs. 1)
L Which means you need more data to get
the same statistical power
(assuming that the fixed-shape model you would
assume was in fact ÒcorrectÓ)
L Freedom to get any shape in HRF results
can give weird shapes that are
difficult to interpret