fmri.searchlight function

Searchlight signal detection

Detection of activated regions using searchlights.

fmri.searchlight(spm, alpha = 0.05, radius, minimum.signal = 0,
   kind = c("abs", "squared"))

Arguments

• spm: fmrispm object
• alpha: multiple test (over volume) adjusted significance level.
• radius: radius of searchlight. Value needs to be larger or equal than 1.
• 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.
• kind: Kind of statistics used for aggregation over search light region. "abs" specifies averaging of absolute voxelwise t-statistics while "squared" corresponds to averaging of squares of these statistics.

Details

The function computes mean statistics (depending on kind) over a searchlight region of radius radius. Approximate voxelwise p-values are determined with respect an empirical (simulated) distribution of the searchlight statistics under the null hypothesis a central t-distributed spm. Thresholding used FDR with rate alpha.

Returns

Object with class attributes "fmripvalue" and "fmridata" - pvalue: voxelwise p-value if exceeding FDR-critical value, 1 otherwise.

• weights: voxelsize ratio

• dim: data dimension

• hrf: expected BOLD response for contrast (single stimulus only)

References

Kriegeskorte, N.; Goebel, R. & Bandettini, P. (2006) Information-based functional brain mapping, PNAS 103:3863-3868.

Author(s)

Joerg Polzehl polzehl@wias-berlin.de

See Also

fmri.lm, fmri.pvalue, fmri.cluster

Examples

## Not run: fmri.searchlight(fmrispmobj)