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