Regarding 'task related motion' -
is it not the case, that one would usually convolve
task induced activations with some hrf while task related motion would affect
the images immedately? Of course, one might venture that not just one scan will
be affected by motion and thus the delay introduced by the hrf (probably at the
order of 1-2 TR) would be 'eaten up'...
Just a thought,
Helmut
----- Original Message -----
Sent: Wednesday, May 04, 2005 2:15
PM
Subject: Re: Motion Correction
3) how should task-correlated motion be dealt with?
is
some degree of correlation to be expected, given
that in most
paradigms, subjects are required to make
some kind of overt
response?
Task related motion should be dealt with in
pretty much the same way as any
other confounding effect in the
statistical model. If you don't model the
confound, then you accept that
the significant differences you see could be
explained by the confound.
If you do model the confound, then you risk any
real effects being
explained away by the confound.
One can also try to
deal with these issues at the level of design - in particular, if you know
that there is going to be task-correlated motion, then you can use an
event-related design to try to decouple the motion from the task-induced BOLD
signal, taking into account the fact that the induced signal is delayed with
respect to the effects of motion. People have used this approach, for example,
to allow subjects to speak in the scanner.
cheers
russ
---
Russell A. Poldrack, Ph.d.
Assistant Professor
UCLA Department of
Psychology
Franz Hall, Box 951563
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phone: 310-794-1224
fax: 310-206-5895
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web: www.poldracklab.org /fontfamily>