Leave that trial type out of that run. When you create your contrasts,
make sure the contrasts add to 1. This insures that the number of runs
that contains the task has minimal influence on your results. If you
are comparing 2 tasks, make sure the sum of the positive values sums
to 1 and the negative values sum to negative 1. If you don't do this,
then subjects with more runs of a trial will have a larger response
even if the betas are the same simply based on the contrast.
Best Regards, Donald McLaren
=================
D.G. McLaren, Ph.D.
Research Fellow, Department of Neurology, Massachusetts General Hospital and
Harvard Medical School
Postdoctoral Research Fellow, GRECC, Bedford VA
Website: http://www.martinos.org/~mclaren
Office: (773) 406-2464
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On Wed, Oct 24, 2012 at 8:13 AM, Anne Schobert
<[log in to unmask]> wrote:
> Dear spm experts,
>
> I would appreciate your advice on how to model a design with missing values:
> In my experiment the participant saw movies of facial expressions and had to
> indicate which emotion he perceived (the six basic emotions or " other"). I
> want to model the brain activation during the movies according to the
> subjective classification of emotion. I have several runs (and several
> scanning days) that I want to put together in one model. The problem is
> that in some runs not every type of emotion has been chosen, and therefore
> the respective regressor would be empty in that run.
>
> I would appreciate any help!
> Anne
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