On Mon, 11 Sep 2000, Stefan Kiebel wrote:
> Dear Esa,
>
> > 1) I used The Full Monty.. model. After analysis I chose SVC and
> > Search Volume... Image. Then I selected manually created mask image.
> >
> > 2) I tried explicit masking in The Full Monty... model using the same
> > manually created mask image. Otherwise the Full Monty... model was the
> > same as earlier.
> >
> > The statistics (Z-scores and p-values) were similar but not quite the
> > same. Search volume and the number of resels were slightly different
> > between SVC and explicit masking. The activated clusters were located in
> > the same places and the number of voxels in each cluster were almost the
> > same.
> >
> > What causes the slight differences between explicit masking and SVC?
>
> There can be slight differences between the estimated p-values between
> your analyses 1 and 2. As far as I can tell from Karl's code, he
> estimates the smoothness within the VOI in the SVC routine based on the
> smoothness estimate of the full volume. This means that the estimated
> FWHM (and therefore resels and corrected p-values) between your two
> analyses can differ slightly. I cannot explain your observation of
> different search volumes, though.
>
> >
> > In my opinion, explicit masking can be used to visualize SVC
> > results. Any comments on this?
>
> Do you mean by this that one could visualize on the MIP only those
> suprathreshold voxels belonging to the VOI?
>
>
Yes. But I think that Geraint just proved my opinion wrong. I had
such a big mask image that results were similar.
Esa
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
|