Mike,
> I have installed these modifications and they now work very well.
> It seems that it's possible to exert complete control of the
> conjunction via the three options.
Great. Glad to hear it.
> However, why is it not possible to specify the spatial extent? I
> accept that in terms of conjunction analysis that might violate some
> primary rule but an explanation would be welcome - I'd like to tidy
> up some of the results by excluding single voxels/small
> clusters.
Good point. There is no reason to forbid it, though there is no
theory to provide the P-values. You should be able to apply an
arbitrary threshold. If you delete " & nc == 1" from line 540 of the
revised spm_getSPM.m you should be asked for an extent threshold.
If you use an Intermediate or the Global Null, you'll get no P-values,
as there is no theory for conjunction spatial extent (yet... Keith
Worsley had a student working on it). If you use the Conjunction Null
you'll get P-values, but they'll be wrong, fortunately, in the
conservative direction.
(Background: The random field theory for obtaining the P-values will
be assuming that the statistic image is not a conjunction, rather just
a single statistic image. Since a conjunction is effectively an
intersection of images, and, all things equal, an intersection of
images will have smaller clusters than a single image, the actual
clusters will be smaller than the theory expects, and hence the
P-values will be too large).
Please implient this change in spm_getSPM.m and let me know if works.
If it does, I'll post the change to spm2_updates.
> Also, is there a preprint of the manuscript explaining the
> intermediate stage, alluded to below?
It should be appearing soon, but maybe Karl/Will can post it?
-Tom
-- Thomas Nichols -------------------- Department of Biostatistics
http://www.sph.umich.edu/~nichols University of Michigan
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-------------------------------------- Ann Arbor, MI 48109-2029
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