¥ 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 (ÒholdÓ)
c) subject gets cue #2, emits response
å 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
åimpossible 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 ÒsignificantÓ? Good
question.