Comparing to zero

[Dr. Jose Luis Patino Vilchis]

We are also working with coherences. I would be interested to know more about
the algorithm embedded in the function and to know how you use it to find
significant coherence. Could it bepossible to have more information on this?

Many Thanks

Luis Patino
Universitätsklinikum Freiburg


Quoting Tom Holroyd <tomh at KURAGE.NIMH.NIH.GOV>:

> > What would be the best way to find clusters that are significally
> > different from zero?
>
> One way is to to a group analysis using AFNI.  I'm using that for
> coherences---here's a snippet.
>
> ...
> [source] = sourceanalysis(cfg, freq);
> [source] = sourcedescriptives([], source);
>
> brikname = 'blah';
> [err, errmsg, info] = writesourcebrik(source, source.avg.coh, brikname);
> if err
>          disp(errmsg)
> end
>
> I've attached writesourcebrik.m, which sets things up to write a brik in a
> format that is compatible with CTF datasets, although that's not really
> important.  It uses a function called WriteBrik.m from the AFNI library, you
> can
> get that from the same website where you get AFNI.  Once you have a set of
> datasets in BRIK format, you can do the test using 3dttest.  You have to
> first
> warp all your datasets to some common space such as Talairach or MNI (AFNI is
>
> more at home with Talairach), using adwarp.  Then something like
>
> 3dttest -prefix outname -base1 0 -set2 subj1+tlrc subj2+tlrc ... subN+tlrc
>
> will do the test.  There's a randpermute function that does the
> non-parametric
> correction on our website, too, at kurage.nimh.nih.gov.
>
> --
> Dr. Tom Holroyd
> "A man of genius makes no mistakes. His errors are volitional and
> are the portals of discovery." -- James Joyce
>