Dear freesurfers

Have you ever tried to get an average retinotopic map across all subjects on freesurfer's standard surface (fsaverage)?

I obtained an individual map for each subject using the fsfast stream (mkanalysis-sess, selxavg3-sess) and plotted the results using
rtview: e.g.

rtview.sh --s subj1 --lh --polar --real polar/real.nii.gz --imag polar/imag.nii.gz --fsig polar/fsig.nii.gz

Now for the group map, my initial idea was to sample each subject's real and imaginary component to the fsaverage surface and average them separately across subjects.
However, I am not sure how I would threshold such an average map on fsaverage using rtview (i.e. what would I use as fsig.nii) given that averaging log p-values
is probably not a good idea.

Within each subject's rtopy.self.?/polar(or /eccen) folder the following files (and few more but probably not important here) exist:

fsig.nii 	-> I understand this contains the unsigned log p values probably obtained via an F-test (frequency of interest) / (noise frequencies)
sig.nii		-> this might then be the signed counterpart of fsig.nii	
imag.nii 	-> this must contain the imaginary component of the polar angle or eccen map
real.nii  	-> this must contain the real component of the polar angle or eccen map
mag.nii 	-> I suppose this might contain the amplitude of the signal at the frequency of interest (i.e. the frequency the wedge / ring is traveling)


However, I don't quite know what the remaining files are good for

iminsig.nii
minsig.nii
cwmap-imag.nii
cwmap-real.nii

ces.nii
cesmag.nii
cesmagpct.nii
cespct.nii
cesvar.pct
cesvarpct.nii

For the ces* files I understand that they generally contain effect sizes / variances and are used for group analyses.
However, I am not quite sure what effects they correspond to in the case of retinotopy.

When browsing the web for similar problems I found the following post:

	> Hi Michelle, try this:
	>
	> isxconcat-sess -sf sessidlist -a rtopy.fsaverage.lh -call -o retgroup
	>
	> cd retgroup/rtopy.fsaverage.lh
	>
	> mri_glmfit --y eccen/ces.000.nii.gz --osgm --o eccen/glm.real --surface 
	> fsaverage lh
	> mri_glmfit --y eccen/ces.001.nii.gz --osgm --o eccen/glm.imag --surface 
	> fsaverage lh
	> mri_glmfit --y polar/ces.000.nii.gz --osgm --o polar/glm.real --surface 
	> fsaverage lh
	> mri_glmfit --y polar/ces.001.nii.gz --osgm --o polar/glm.imag --surface 
	> fsaverage lh
	>
	> mri_fieldsign --fs lh.fieldsign.mgh \
	>  --eccen eccen/glm.real/osgm/gamma.mgh eccen/glm.imag/osgm/gamma.mgh \
	>  --polar polar/glm.real/osgm/gamma.mgh polar/glm.imag/osgm/gamma.mgh \
	>  --s fsaverage --hemi lh --sphere --old
	>
	> tksurfer fsaverage lh inflated -aparc -ov lh.fieldsign.mgh -fthresh .5

However, as mentioned above I wonder what effect sizes are used here and why (different to rtview) there is no significance map
needed to plot the data.

Is there a way to use rtview for the result of a group analysis?
And if yes how would I get a fsig.nii file for that?

I really appreciate your help!

many thanks & best wishes

Andreas