FDR control is an alternative to the more conservative “family-wise error” control for multiple comparisons. Historically, SPM has aimed to control FDR on voxels (the expected fraction of false-positive/total-positive decisions made about individual voxels in an image). In the coming months this will be superseded by FDR control of topological properties of the signal (i.e. control of properties that pertain to the spatial organization of activations - e.g. height and extent - and are not reducible to individual voxels). SPM will initially be able to identify significantly voluminous blobs according to a decision procedure that controls spatial-extent FDR. Thus, on average, the fraction of blobs falsely deemed to have significant spatial extent is controlled beneath say 5/100 = .05 or 1/100 = .01. Work-in-progress is examining the possibility of FDR control over local maxima.
 

J. Chumbley and K. Friston. False discovery rate revisited: FDR and topological inference using Gaussian random fields. Neuroimage, 2008. In Press.
 
These descriptions of the new features are taken from the SPM8 Release Notes
 
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