postgroupcoeff {BHMSMAfMRI}R Documentation

Obtain posterior group coefficients using the BHMSMA methodology.

Description

Computes posterior group coefficients using the BHMSMA methodology.

Usage

postgroupcoeff( nsubject, grid, GLMCoeffStandardized, PostMeanWaveletCoeff, 
wave.family="DaubLeAsymm", filter.number=6, bc="periodic" )

Arguments

nsubject

Number of subjects included in the analysis.

grid

The number of voxels in one row (or, one column) of the brain slice of interest. Must be a power of 2. The total number of voxels is grid^2. The maximum grid value for this package is 512.

GLMCoeffStandardized

An array of dimension (nsubject, grid, grid), containing for each subject the standardized GLM coefficients obtained by fitting GLM to the time-series corresponding to the voxels.

PostMeanWaveletCoeff

A matrix of size (nsubject, grid^2-1), containing for each subject the posterior mean of the wavelet coefficients of all levels stacked together (by the increasing order of resolution level).

wave.family

The family of wavelets to use - "DaubExPhase" or "DaubLeAsymm". Default is "DaubLeAsymm".

filter.number

The number of vanishing moments of the wavelet. By default 6.

bc

The boundary condition to use - "periodic" or "symmetric". Default is "periodic".

Details

The wavelet computations are performed by using R package 'wavethresh'. For details, check wavethresh package help.

Value

A list containing the following.

groupcoeff

A matrix of dimension (grid, grid), containing the posterior group coefficients obtained by BHMSMA methodology.

Author(s)

Nilotpal Sanyal <nsanyal@stanford.edu>, Marco Ferreira <marf@vt.edu>

References

Sanyal, Nilotpal, and Ferreira, Marco A.R. (2012). Bayesian hierarchical multi-subject multiscale analysis of functional MRI data. Neuroimage, 63, 3, 1519-1531.

Examples

nsubject <- 3
grid <- 8
GLMCoeffStandardized <- array(rnorm(3*8*8),dim=c(3,8,8))
PostMeanWaveletCoeff <- array(rnorm(3*63),dim=c(3,63))
post.groupcoeff <- postgroupcoeff( nsubject, grid, GLMCoeffStandardized, PostMeanWaveletCoeff)
dim(post.groupcoeff$groupcoeff)
#[1] 8 8

[Package BHMSMAfMRI version 1.3 Index]