>
>>
>> 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
Los Angeles, CA 90095-1563
phone: 310-794-1224
fax: 310-206-5895
email: [log in to unmask]
web: www.poldracklab.org
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