The pickatlas is used during statistical inference (viewing of the
results), not during analysis specification (pre-Results). When a ROI
is specified using the pickatlas during viewing of the results, the
number of voxels entering into the statistical computation for multiple
comparisons is reduced based on the size of the ROI (the pickatlas
implements the SPM small volume correction for the ROI). An additional
small volume correction does not need to be applied. Either FWE or FDR
can be used with the ROI. The resulting "corrected" P-values will be
corrected for multiple comparisons based on the size of the ROI. The
uncorrected P-values remain unchanged.
Specifying an explicit mask at the time of analysis specification (or
statistical estimation) reduces the number of voxels entering into the
analysis from the outset. There should not be a need to use a pickatlas
ROI in this case during result viewing unless you want to further refine
the hypothesis. In either case, the masks/ROI are affecting the number
of voxels entering into the computation for multiple comparisons (the
shape of the ROI also is involved for the small volume correction).
Viewing the results without a pickatlas ROI, and then using the SPM SVC
with some user-defined ROI should give similar results to using that
same ROI through the pickatlas.
Incidentally, the pickatlas is SPM5 compatible. The latest release also
includes List.mat and Border.mat files for each of the included atlases,
that allow them to be used with the very useful gin_clusters routine
from aal.
Hope that helps
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Joseph A. Maldjian, MD
Professor, Dept. of Radiology and Biomedical Engineering
Director Advanced Neuroscience Imaging Research Core (ANSIR)
Wake Forest University School of Medicine
Office: 336 716-2815
fax: 336 716-2870
email: [log in to unmask]
website: www.ansir.wfubmc.edu/maldjian.htm
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-----Original Message-----
From: SPM (Statistical Parametric Mapping) [mailto:[log in to unmask]]
On Behalf Of K. Prasad
Sent: Wednesday, February 01, 2006 11:28 AM
To: [log in to unmask]
Subject: [SPM] wfu pick atlas vs SVC
Dear SPMers,
Can somebody enlighten me about the difference or
similarity between the WFU_PickAtlas and teh small
volume correction. How does these relate to specifying
an explicit mask at the stage of model estimation.
Many Thanks
-krishna
Krishna P. Miyapuram
Work : Graduate Student, Dept of Anatomy, Univ of Cambridge Home : 25,
Parkside, Room 10 (Phone +44 - 1223 - 476858 Address : Downing College,
Regent Street, Cambridge, CB21DQ, England URL :
http://people.pwf.cam.ac.uk/kpm23/index.html
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