Hi Carlos,
I agree with what Anja said. I would just add that you could try putting
in one of the summary motion measures (eg mean relative motion) in as a
demeaned confound covariate at the higher-level analysis and see what
effect that has.
Cheers, Steve.
On Tue, 20 Jul 2004, Carlos R. Cortes wrote:
> Hi,
>
> I'm new to fsl. I am trying to deal with motion in children.
>
> Here is the situation:
> -Two groups of children (Control group vs. Motion-heavy group)
> -1.5 Tesla Scanner (slices interleaved, TR 2 sec)
> -Three runs, block-design, 3 different conditions (A B C A B C A B C A)
> -Each block is 40 sec long
>
> Problem:
> Several subjects from the motion-heavy group and some from the control
> group have motion of 2-5 mm. The motion is mostly restricted to only one or
> two blocks within a run (e.g. the first A and B blocks or the second B and
> C blocks). I do not want to just exclude the whole run because these motion-
> blocks. To avoid this, I am trying to decide between the following possible
> approaches:
>
> a. Set each block as a different condition and then define motion-blocks as
> covariates of no interest
> b. Remove volumes specific to the motion-blocks
>
> Questions
> 1. What are the possible problems/consequences of these approaches?
> 2. Is there any other option to consider?
>
> It would very useful to hear concepts or suggestion about this regard.
>
> Thanks in advance!
> Carlos
>
Stephen M. Smith DPhil
Associate Director, FMRIB and Analysis Research Coordinator
Oxford University Centre for Functional MRI of the Brain
John Radcliffe Hospital, Headington, Oxford OX3 9DU, UK
+44 (0) 1865 222726 (fax 222717)
[log in to unmask] http://www.fmrib.ox.ac.uk/~steve
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