fmri.cluster: Cluster thresholding.

In fmri: Analysis of fMRI Experiments

Cluster thresholding.

Description

Detection of activated regions using cluster thresholding.

Usage

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

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.
ncmax	maximal cluster size used. An activation is detected if for any clustersize in ncmin:ncmax 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.
verbose	intermediate diagnostics

Details

Approximate thresholds for the existence of a cluster with spm-values exceeding a 1-beta threshold k_{nc,na:ne} for cluster size nc are based on a simulation study under the hypothesis and adjusted for number of voxel in mask and spatial correlation. beta is chosen such that under the hypothesis the combined (over cluster sizes ncmin:ncmax) test has approximate significance level alpha.

Value

Object with class attributes "fmripvalue" and "fmridata"

pvalue	cluster based p-values for voxel that were detected for any cluster size, a value of 1 otherwise.
mask	mask of detected activations
weights	voxelsize ratio
dim	data dimension
hrf	expected BOLD response for contrast (single stimulus only)

Author(s)

Joerg Polzehl [e-mail]

See Also

fmri.lm, fmri.pvalue, fmri.searchlight

Examples

  ## Not run: fmri.cluster(fmrispmobj)

fmri documentation built on Sept. 8, 2023, 5:23 p.m.