External Email - Use Caution
Hello,
I am creating sig.mgh overlays in a group analysis. On this map, I can see some blue and red vertices, corresponding to negative and positive values (respectively) on the map.
On the other hand, I read in the documentation that sig.mgh is a map created by computing -log(p) (base 10, whatever).
That cannot be true, since 0<p<1, hence -log(p)>0.
After some exploration I came up with the following guess: sig.mgh is actually -sign(z)*log(p). (That is of course very useful to quickly interpret the maps.)
Question 1: is this guess correct? Question 2: where is the piece of documentation I missed where this is explained? (I am asking this because I feel like I am missing a lot on the details on the machinery behind FS commands...)
Cheers Antonin
Hôpital Erasme - ULB Cliniques universitaires de Bruxelles Route de Lennik 808 - B - 1070 Bruxelles S http://secure-web.cisco.com/10VoDNoTPVxzoJ9Ip0Jm8M6aDnd42uu8rcy8brYy_9Fx9lBK...
Disclaimer : http://secure-web.cisco.com/130lPkFzkXUa0jrMTavOQz200HGNhc8bjmwk_Mgl3tHuW0QO...
On 11/10/2020 8:25 AM, Rovai Antonin wrote:
External Email - Use CautionHello,
I am creating sig.mgh overlays in a group analysis. On this map, I can see some blue and red vertices, corresponding to negative and positive values (respectively) on the map.
On the other hand, I read in the documentation that sig.mgh is a map created by computing -log(p) (base 10, whatever).
That cannot be true, since 0<p<1, hence -log(p)>0.
After some exploration I came up with the following guess: sig.mgh is actually -sign(z)*log(p). (That is of course very useful to quickly interpret the maps.)
Question 1: is this guess correct?
Yes, it is, for t contrasts. F contrasts will not have a sign.
Question 2: where is the piece of documentation I missed where this is explained? (I am asking this because I feel like I am missing a lot on the details on the machinery behind FS commands...)
I just updated two of the wiki pages where I found this to be incomplete. Not sure how to answer your question about the machinery. FS is a sprawling, complicated suite of tools. We make all the source code available, so that is the ultimate documentation.
Cheers Antonin
Hôpital Erasme - ULB Cliniques universitaires de Bruxelles Route de Lennik 808 - B - 1070 Bruxelles S http://secure-web.cisco.com/10VoDNoTPVxzoJ9Ip0Jm8M6aDnd42uu8rcy8brYy_9Fx9lBK...
Disclaimer : http://secure-web.cisco.com/130lPkFzkXUa0jrMTavOQz200HGNhc8bjmwk_Mgl3tHuW0QO...
Freesurfer mailing list Freesurfer@nmr.mgh.harvard.edu https://mail.nmr.mgh.harvard.edu/mailman/listinfo/freesurfer
freesurfer@nmr.mgh.harvard.edu
-
Douglas N. Greve -
Rovai Antonin