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Dear Dorian,

see inline comments...

Am Mittwoch, den 28.01.2009, 11:50 +0100 schrieb Dorian P:
> Une small addition:
> 
> If I need to try modulation 1-2-3-4-5 and see the regressor effect
> with contrast [0 1],
> can I just run contrast [0 -1] to save another GLM with modulation 5-4-3-2-1 ?

yes

> > I have a simple question. I need to run around 5 GLMs for each subject
> > (N = 19) with different parametric modulation values for different
> > variables.
> > My question is: Is there a way to save time by using some calculations
> > previously done for the subject?
> >
> > I don't know the steps of a GLM, but thinking of SPM, it first
> > establishes the number of resels and then runs the analysis, and
> > thinking that the volumes to analyze are the same for each subject,
> > and though number of resels should be the same... can this be useful
> > to the next GLM? Any clue how to save time?

No. Even if the number of voxels that are considered is the same, the
smoothness of the error (and thus the number of resels) will depend on
the model. However, you should model all effects that you expect to be
in your data in a single model, not in separate models. There may be
reasons to run 2 or 3 models (e.g. some experiments may be modeled
either as block or event related), but there is no way to shorten the
analysis time.

Volkmar

-- 
Volkmar Glauche
-
Department of Neurology         [log in to unmask]
Universitaetsklinikum Freiburg  Phone   49(0)761-270-5331
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79106 Freiburg                  http://fbi.uniklinik-freiburg.de/