Your idea made me think of adding more and more pametric modulations
for a single condition. But would it be possible to skip a level of
pmod(1) = 1-2-3-4-5
pmod(2) = 1-2-3-4(-0) (!!?)
Should I put '0' to a level to account the remaining 4 levels or
should I add another condition with a new parametric modulation with
only 4 levels of modulation?
And one more question. Is it reasonable to use modulation 2-1-1-2 with
contrast "-1" to account for the modulation 1-2-2-1? I am asking
because they are not linear as the previous example.
Thank you very much for you help.
2009/1/28 Volkmar Glauche <[log in to unmask]>:
> 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 ?
>> > 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 Glauche
> Department of Neurology [log in to unmask]
> Universitaetsklinikum Freiburg Phone 49(0)761-270-5331
> Breisacher Str. 64 Fax 49(0)761-270-5416
> 79106 Freiburg http://fbi.uniklinik-freiburg.de/