¥ Assume a fixed shape h(t ) for the HRF
H e.g., h(t ) = t 8.6 exp(-t/0.547) [MS Cohen, 1997]
H Convolved with stimulus timing (e.g.,
AFNI program waver), get ideal response function r(t )
¥ Assume a form for the baseline
H e.g., a + b×t for a
constant plus a linear trend
¥ In each voxel, fit data Z(t ) to a curve of the form
¥ Z(t ) È a + b×t + b× r(t
)
¥ a, b, b are unknown parameters to be
calculated in each voxel
¥ a,b are ÒnuisanceÓ parameters
¥ b is amplitude of r(t ) in data = Òhow muchÓ BOLD