This program computes the actual maps. Statistical, significance, and parametric maps for all of your subjects on individual basis can be computed. (Note that the same program with the different options is used for the group analysis – see the FsFast for more details). The map is computed from a given analysis and contrast. Significance results are stored as log 101 unless you specify otherwise using the -pxform option.

In your Study Directory, you would run stxgrinder-sess with the following options:

-analysis analysisname

name of analysis from Step7

-contrast contrastname

name of contrast from Step 9

-sf sessid

from Step 3

-df sesspar

from Step 3

For Bert, type the following:

stxgrinder-sess –contrast omnibus –analysis sem_assoc –sf sessid –df sesspar

This step takes about 2 minutes to complete.

OUTPUT: This will create a subdirectory called omnibus under the bold/analysisname directory for each session. Within this directory, you will find six new volumes with stems f, fsig, t, sig, minsig, and iminsig.

f - value of the F ratio
fsig – significance of the F-test
t – stores the variate-by-variate t-statistic (value of the t ratio)
sig- significance of the t-test, which will be determined by default (possibly multiple maps for multiple post-stimulus delays)
minsig – looks for best significance, i.e., time at which best significance occurred for each voxel, using the Benferroni corrected t-test
iminsig- tells you in which frame the best significance was found; the index of the best t-test significance at each voxel.

Each map contains the frames of the points on graph (see Appendix A). The number of frames in each map is determined by the values you set for -timewindow and –prestim commands in mkanalysis (i.e., 1 image per TR in time window). There are 12 different significance maps.

The variate-by-variate t-statistic is stored in the t volume and its significance is stored in the sig volume. The variate is a time-point (or ideal hemodynamic curve). Multiple variates only apply to event-related design. In addition, the best variate (as measured by the minimum significance) at each voxel is also determined and stored as a map (after Benferroni correction) in the minsig volume. The index of the best variate is stored in the iminsig volume. In subsequent stages, you will be required to enter a map – this refers to one of these volumes.

FsFastTutorialV4.5/920_Compute_statistical_maps_of_the_omnibus_contrast (last edited 2011-05-19 15:29:07 by NickSchmansky)