Hi Jesse
Yep, it's normal procedure to use your main effects 'blob' as a seed for a PPI.
Actually the PPI regressor won't be completely orthogonal to your task contrast but since you include the task regressor in your model, any variance assigned to the PPI contrast should *not* be driven by shared main effects of task.
Jill
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Dr Jill O'Reilly
FMRIB Centre, Dept Clinical Neurology, Oxford University
Phone +44 1865 222466
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From: Jesse Brown <[log in to unmask]<mailto:[log in to unmask]>>
Date: 15 February 2010 22:41:42 GMT
To: [log in to unmask]<mailto:[log in to unmask]>
Subject: [FSL] PPI seed region from FEAT cluster?
Reply-To: FSL - FMRIB's Software Library <[log in to unmask]<mailto:[log in to unmask]>>
Hi all,
I'm running a PPI and debating between different methods of seed region
selection. I've run a group FEAT for a contrast of interest and found a
cluster of activation in the hippocampus. Can I use this cluster as my seed
for a PPI analysis on the same contrast? This seems valid to me because the
PPI regressor is orthogonal to the psychological regressor but I'm not
certain and want to avoid any circularity.
Thanks!
Jesse
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Stephen M. Smith, Professor of Biomedical Engineering
Associate Director, Oxford University FMRIB Centre
FMRIB, JR Hospital, Headington, Oxford OX3 9DU, UK
+44 (0) 1865 222726 (fax 222717)
[log in to unmask]<mailto:[log in to unmask]> http://www.fmrib.ox.ac.uk/~steve
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