PowerPoint Presentation - Time Series Analysis in AFNI

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• 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 ) » a + b×t + b× r(t )

• a, b, b are unknown parameters to be calculated in each voxel

• a,b are “nuisance” parameters

• b is amplitude of r(t ) in data = “how much” BOLD

Simple Regression Models