PowerPoint Presentation - Time Series Analysis in AFNI

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• Can have activations with multiple phases that are not always in the same time relationship to each other; e.g.:

a) subject gets cue #1

b) variable waiting time (“hold”)

c) subject gets cue #2, emits response

Â which depends on both cue #1 and #2

H Cannot treat this as one event with one HRF, since the different waiting times will result in different overlaps in separate responses from cue #1 and cue #2

H Solution is multiple HRFs: separate HRF (fixed shape or deconvolution) for cue #1 times and for cue #2 times

o Must have significant variability in inter-cue waiting times, or will get a nearly-collinear model

Âimpossible to tell tail end of HRF #1 from the start of HRF #2, if always locked together in same temporal relationship

o How much variability is “significant”? Good question.

Advanced Topics in Regression

timing of events

is known