Hi Joe - just a quickie on this: no, the % output by Featquery, which you
get if you turn on the % option, is a real % - it doesn't need dividing by
100.
Note that you can sometimes get very high % if your mask includes the edge
of the brain, as you can get big signal changes with quite low original
signal level.
Cheers.
On Wed, 25 Aug 2004, Joseph Devlin wrote:
> Hi Zach,
>
> Personally I've never seen mean % bold signal change values (from a region)
> as high as 2%. They typically range from -1 to 1%, in my experience,
> although there are larger values reported in the literature. So an effect
> of 0.7% would be a strong effect, in my experience.
>
> Obviously if you combine the featquery and effect.sh techniques, you'll get
> some kind of hybrid. Perhaps Steve can correct me if I'm wrong, but the
> output of featquery needs to be divided by 100 to turn it into a
> percentage, even when you check the "% signal" option. Even so, that would
> imply an effect of 1.45% which still isn't 2.0% nor is it the 0.7% from the
> effect.sh script.
>
> I don't know why featquery and effect.sh give different results -- they
> shouldn't, particularly not by a factor of 2!
>
> Joe
>
Stephen M. Smith DPhil
Associate Director, FMRIB and Analysis Research Coordinator
Oxford University Centre for Functional MRI of the Brain
John Radcliffe Hospital, Headington, Oxford OX3 9DU, UK
+44 (0) 1865 222726 (fax 222717)
[log in to unmask] http://www.fmrib.ox.ac.uk/~steve
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