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
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