Dear SPMers,
I apologize for repeating a question that has been asked twice now in the list
before, but I haven't seen an answer that is clear to me.
I'm writing some custom analysis scripts and I'm wondering how it is that
clusters are defined in SPM. Specifically, what is the requirement for a voxel
to be considered to be part of a cluster. It seems from looking at
spm_clusters.m and spm_bwlabel.m (I don't know C and so can't make sense of
spm_bwlabel.c) that they can be defined as 6(surface), 18(edge), or 26(corner)
and that SPM uses 18(edge) by default. The problem is that I'm not sure I know
what this means.
Is it that surface means adjacent voxels must have two (of 3) coordinates in
common and be adjacent on the third dimension, edge means adjacent voxels must
have one coordinate in common and be adjacent on the other two, and corner
means that they need have no voxels in common but must be adjacent on all
dimensions?
Thanks in advance for any help,
Jared Van Snellenberg
Laboratory for Affective & Developmental Neuroscience (www.sfu.ca/ladn)
Department of Psychology, Simon Fraser University
RCB 4209, 8888 University Drive,
Burnaby BC, Canada V5A 1S6
Phone: 604-291-3013
Fax: 604-291-3427
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