> There's evidence (Lowe MJ & Sorenson JA, Magn Reson Med. 1997 37:723-9)
> that the spatial smoothing can be deferred until after statistical
> analysis
One complication for consideration is that smoothing BOLD fMRI data (in
space) alters the shape of the intrinsic temporal autocorrelation (in time)
present in each voxel. This is because power at low frequencies (under the
null-hypothesis) tends to share phase across space, while power at higher
frequencies does so to a lesser extent. (see: Aguirre GK, et al. Neuroimage
1997; 5: 199-212.)
As regards your question, I would think that smoothing the data and
smoothing the statistical map could not be rendered equivalent in any simple
way, as smoothing the data actually alters the degrees of freedom of the
test statistic (due to alterations in the modeled noise power spectrum).
I'm eager to hear what the SPM gurus have to say about this,
Geoff
--
Geoffrey Karl Aguirre, M.D., Ph.D.
University of Pennsylvania Center for Cognitive Neuroscience
3815 Walnut Street Fax: (215) 898-1982
Philadelphia, PA 19104-6196 mailto:[log in to unmask]
http://ccn.upenn.edu/~aguirre
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