Cluster thresholding.

Detection of activated regions using cluster thresholding.

fmri.cluster(spm, alpha = 0.05, ncmin = 2, minimum.signal = 0)

Arguments

spm	fmrispm object
alpha	multiple test (over volume and cluster sizes) adjusted significance level used for thresholds.
ncmin	minimal cluster size used. An activation is detected if for any clustersize in nvmin:20 the size specific threshold is exceeded.
minimum.signal	allows to specify a (positive) minimum value for detected signals. If minimum.signal >0 the thresholds are to conservative, this case needs further improvements.

Details

Approximate thresholds for the existence of a cluster with mean t-statistics exceeding a 1-beta threshold k_{nc} for cluster size nc are based on a simulation study under the hypothesis and adjusted for both degrees of freedom, number of voxel in mask and spatial correlation. beta is choosen such that under the hypothesis the combined (over cluster sizes ncmin:20) test has approximate significance level alpha.

Value

Object with class attributes "fmripvalue" and "fmridata"

pvalue

p-values of voxelwise t-statistics for voxel that were detected for any cluster size, a value of 1 otherwise.

weights

voxelsize ratio

dim

data dimension

hrf

expected BOLD response for contrast (single stimulus only)

Author

Joerg Polzehl polzehl@wias-berlin.de

See also

fmri.lm, fmri.pvalue, fmri.searchlight

Examples

  if (FALSE) fmri.cluster(fmrispmobj)