Hi Ben
In the attention dataset I don't think that you can
add/subtract any two regressors and get the other
regressor as a result, they are independent.
Nia
--- "Xu, Ben (NIH/NINDS) [E]" <[log in to unmask]>
wrote:
> Thanks, Nia, for your quick response. But, isn't
> this how one creates
> the "input" regressor for DCM? (see the attached
> design matrix for the
> "attention" data.)
>
> Ben
>
> -----Original Message-----
> From: Nia Goulden [mailto:[log in to unmask]]
> Sent: Thursday, August 17, 2006 9:39 AM
> To: [log in to unmask]
> Subject: Re: [SPM] DCM design matrix
>
> Hi Ben
>
> I think the error you're getting is telling you that
> your first regressor is a linear combination of
> regressors 2,3,4 and 5 i.e. when you put these
> regressors together then you get the first
> regressor.
> The regressors are therefore not independent.
>
> Hope this helps
> Nia
>
>
> --- "Xu, Ben (NIH/NINDS) [E]" <[log in to unmask]>
> wrote:
>
> > Hi,
> >
> > I have asked the question earlier but have not
> > gotten a response. I'm
> > trying to use DCM for an fMRI study and have a
> > question related to the
> > design matrix prior to DCM analysis.
> >
> > I created a design matrix (attached) with 7
> > regressors (i.e.,
> > conditions) and an implicit baseline. The 1st
> > regressor shares common
> > input with regressor 2-5, and will be used for the
> > "input drive" to the
> > intrinsic connections. (Regressors 6-7 will not be
> > included in the DCM
> > analysis.)
> >
> > Questions:
> > 1. As I understand, it's ok to have a
> non-orthogonal
> > design matrix for
> > DCM analysis. Is that correct?
> >
> > 2. The design matrix indicates regressors 1-5 are
> > "not uniquely
> > specified" and, therefore I can't define contrasts
> > in "Results." I have
> > tried the "attention" dataset provided at the SPM
> > Web site
> > (http://www.fil.ion.ucl.ac.uk/spm/data/). Its
> design
> > matrix is
> > non-orthogonal, either. However, there is no
> warning
> > on regressors "not
> > uniquely specified." And it allows t contrasts in
> > Results. What's wrong
> > with my design? Will it affect the DCM analysis?
> >
> > Any help is greatly appreciated.
> >
> > Ben
> >
>
>
>
>
>
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