Dear Roland,
Have I got it right, that the regressor it self is present but just some values are not displayed, i.e. that the regressor has the same 'grey'-level during that trial as it has when the trial is not presented?
Could it be, that these missing values are similar to the mean RT? Since the regressors are mean corrected, this values will somewhat disappear in the display.
Good luck,
Karsten
Roland Zahn <[log in to unmask]> schrieb am 11.01.06 21:56:30:
>
> Dear SPM experts,
>
> I have another question regarding parametric modulation of the trial
> specific HRF in SPM5 and greatly appreciate any help.
>
> For the 1st level analysis under fMRI model specification:
>
> My design matrix contains 3 sessions, 4 trial types including null events
> (HRF with spatial and temporal derivative)
> and for each of the 3 trial types (not null events) I have defined several
> modulating parameters.
> One of the parameters is Reaction Time (in millseconds) for each stimulus
> and trial.
>
> Surprisingly after running the model (in bacth mode) and exploring the
> design matrix before estimation (I redid this 3 times), the design matrix
> would skip the Reaction Time parameter for some trials in some runs and
> keep it for others.
>
> Is there any reasonable explanation for this ?
>
> Thanks for any help !!
>
> Best,
> Roland
>
> Roland Zahn, Dr. med.
> NIH / NINDS
> Cognitive Neuroscience Section
> Building 10, 5C206
> 10 Center Drive, MSC 1440
> Bethesda, MD 20892-1440
> Tel.: (+1)-301-402-6392
> Fax.: (+1)-301-480-2909
--
-------------------------------------------------------------
Karsten Specht, PhD
Department of Biological and Medical Psychology
& National Competence Centre for functional MRI
University of Bergen
Jonas Lies vei 91
5009 Bergen
Norway
Tel.: +47-555-86279
Fax: +47-555-89872
[log in to unmask]
http://fmri.uib.no/
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