SPM Papers

Statistical Parametric Mapping


Written by members of the Wellcome Department of Imaging Neuroscience

Assessing the Significance of Focal Activations Using their Spatial Extent

Friston KJ, Worsley KJ, Frackowiak RSJ, Mazziotta JC, Evans AC (1994)
Human Brain Mapping 1:214-220


Current approaches to detecting significantly activated regions of cerebral tissue use statistical parametric maps, which are thresholded to render the probability of one or more activated regions of one voxel, or larger, suitably small (e.g. 0.05). We present an approximate analysis which gives the probability that one or more activated regions of a specified volume, or larger, could have occurred by chance. These results mean that the detection of significant activations no longer depends on a fixed (and high) threshold but can be effected at any (lower) threshold, in terms of the spatial extent of the activated region. The substantial improvement in sensitivity which ensues is illustrated using a power analysis and a simulated phantom activation study.

Digital manuscripts

Manuscript SPM_2.ps.gz SPM_2.pdf
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Note that the manuscript is presented as submitted, which may differ from the published version.
Changes made in proof or during the review cycle may not be included in the manuscript.

There is a typo in Eqn.4 of this manuscript, which is missing a factor of pi**(-(D+1)/2).
It is correct in the published version.

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