Dear Rafael
I think you have a point. I have just had a short look at this and
sometimes negative onsets are treated correctly try for instance an
onset of -120s and a duration of 60s, then you get a perfectly flat
line. On the other hand if you have an onset of -40s and a duration of
60s you still get an initial overshoot around 10s. I have not been
able to find the code where this happens, but maybe others can help.
Best
Torben
Den 11/08/2009 kl. 11.07 skrev Rafael Lüchinger:
> Hi Torben
>
> Thanks for your answer.
> Indeed I can give SPM an negative onset. I observe a correct
> designmatrix after design definition. But after estimating the
> design, the designmatrix looks diffrent - the negative onsets were
> ignored - an I have a convolution starting from 0 (with the overshot
> at 6s, of which I want to get rid of).
>
> If I look at your design matrix, I see a difference, but if you plot
> the -10s-onset regressor, I guess you have a concolution from 0 on.
> Isn'it ?
>
> Rafael
>
>
>
> On Mon, 10 Aug 2009 11:19:06 +0200
> Torben Ellegaard Lund <[log in to unmask]> wrote:
> Dear Rafael
> I don't think your observation is correct. In the attached file
> you se
> two designmatrices. In the first the onsets in the designmatrix are
> 0s
> and 50s with 30s duration. In the second designmatrix the onsets
> are -10s
> and 50s with 30s duration. I think it is clear that the two models
> differ.
> Best
> Torben
> Den 07/08/2009 kl. 14.34 skrev Rafael Lüchinger:
> > Hi spm pros first, thanks to roberto for answering my question
> > (totally correct). Therse's another problem: What can I do when my
> > condition starts before my first scan? In a resting state experiment
> > the BOLD signal does not follow an overshot at scan # 0. The BOLD
> > fluctuation in this state started ~half a minute earlier. The
> > regressor should be convolved since the condition alters later (eyes
> > open(closed). What I should have is a regressor that gets through
> > the standard procedere but starts 20 seconds before the first scan
> > of the analysis. I tried a negative value as onset but it gets
> > interpreted as zero in spm. Thanks for any help Rafael
>
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> Rafael Lüchinger, MSc UZH
>
> Brain Mapping Research
> University of Zuerich, Department of Child and Adolescent Psychiatry
> Neumuensterallee 9/ Fach, CH-8032 Zuerich, Switzerland
> Phone: (+41) 43 499 26 50 Fax: (+41) 43 499 26 04
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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