[caret-users] fMRI mapping & t-values
donna at brainvis.wustl.edu
Tue Jun 19 07:40:07 CDT 2007
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:
Is the 4.67 hot spot in the left or right hem?
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.
> --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
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> caret-users at brainvis.wustl.edu
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