Dear Nicholas,
On Mon, 28 Feb 2005, Nicholas Masse wrote:
> surely makes sense from a statistical standpoint. However, and this may be
> because of my own naivety, I'm wondering how the Conjunction null hypothesis
> fits from a neuroanatomical standpoint. I'm assuming that the conjunctional
...
> eventhough all 10 subjects have activation in the same area. I guess my big
> beef, and I may have the reasoning all wrong, is that the conjunction null
> looks at a voxel to voxel comparison when I'm more interested in the
> activity in a certain area. So would the Global null, since its more
> sensitive, be more representative of area activation? Maybe people on the
> list can correct my assumptions if need be....any thoughts would be good.
the problem of spatial variability is a completely different one and
doesn't have much to do with one conjunction hypothesis or the other. It
also arises if you do any other group statistics. SPM (and probably
other voxel-based stats software too) implies some assumptions for
group statistics: 1) your measured signal is not independent in
neighbouring voxels - in most cases, this is true for fMRI BOLD effects.
2) spatial normalisation does a rather good job in warping individual data
to a standard space. 3) You do lots of smoothing on your data before
statistics - this should at least make your areas of interest overlap in
all subjects.
--
Volkmar Glauche
-
Department of Neurology E-Mail [log in to unmask]
UKE Hamburg Phone 49(0)40-42803-5781
Martinistr. 52 Fax 49(0)40-42803-9955
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