[caret-users] fMRI mapping & t-values

Donna Dierker donna at brainvis.wustl.edu
Tue Jun 19 07:40:07 CDT 2007


Hi Katja,

A couple of things come to mind:

* The 4.67 hot spot doesn't intersect the average fiducial surface.  Did 
you map to the average fiducial surface, or use multi-fiducial mapping 
(MFM)?  The latter method is less vulnerable to this problem.

* There could be some very large "spiky" values throwing off the scale.

I can take a quick look and let you know what I think:

http://pulvinar.wustl.edu/cgi-bin/upload.cgi

Is the 4.67 hot spot in the left or right hem?

Donna

On 06/19/2007 05:05 AM, Katja Umla-Runge wrote:
> Dear Caret users,
>
> Mapping spmT*.img files (SPM99) to a surface in Caret, the resulting 
> image seems (at first glance) to fit the data table I obtained from 
> SPM. However, if I set the threshold to say t = 3,61 (metric --> 
> settings --> threshold --> Pos User = 3,61 --> threshold type: User) 
> which is the threshold I got from SPM for a given one-sample t-test, 
> less activations remain as compared to the SPM data table. As an 
> example, my results include an occipital activation with t = 4,67. If 
> I want to see this structure activated on my Caret surface, I need to 
> enter a threshold of about t = 1. Why do t-values and corresponding 
> activations do not correspond between the two systems? How can make 
> them correspond?
> Thank you in advance.
>
> Katja
>
> --Dipl.Psych. Katja Umla-Runge
>
> Saarland University
> Department of Psychology        phone: +49 - (0)681 - 302 4643
> P.O.Box 151150                  fax:   +49 - (0)681 - 302 4049
> D-66041 Saarbruecken            email: k.umla-runge at mx.uni-saarland.de
>
> www.BrainCog.de
>
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