Dear SPMers,
I know this question has been asked before, but it doesn't seem
that there is a lot of recent consensus.
I have done a second-level analysis in SPM2. I was
interested in seeing all of the activated voxels in one of my contrast
images, so I lowered the threshold to T = 1.1 (1.0 results in a crash,
incidentally).
When I did that, I noticed a LOT of activity outside the brain.
I wondered if that activity outside the brain might result from
smoothing, and if so, if masking it out would help boost power.
If masking it out would help boost power, would it be reasonable
to mask the first-level contrast images, and then include the new,
masked contrast images in the second-level analysis?
Or would the approach discussed in 2002 by Stephan Kiebal (via
Tom Nichols,
http://www.jiscmail.ac.uk/cgi-bin/wa.exe?A2=ind02&L=SPM&P=R36174&I=-3) be better? (Below)
(1) Configure, but don't
estimate a model
(2) Modify
SPMcfg.mat...
load SPMcfg.mat
xM.TH = -Inf;
xM.VM = spm_vol('mask_all.img');
save SPMcfg xM -append
(3) Estimate the
model
Any suggestions, including those not mentioned above, would be
appreciated.
Thanks in advance,
Christy
--
Christy Marshuetz
Assistant Professor
Department of Psychology
Yale University
2 Hillhouse Avenue
P.O. Box 208205
New Haven, CT 06520-8205
Phone: (203) 432-4636
