Dear Vadim,
What you can do is add a dummy trial for that otherwise empty condition
at the very end of the session (ie onset = number of scans). It will
stop SPM complaining about it and will let you have all of the design
matrices with the same size. You will still have to adjust the contrasts
so that they always have a zero weight for that condition, and you might
also have to rescale some of the contrasts, see eg slide 12 of:
http://www.fil.ion.ucl.ac.uk/spm/course/slides16-oct/03_Inference.pptx
Best regards,
Guillaume.
On 08/02/17 10:47, Vadim Axel wrote:
> Dear experts,
>
> In my experiment the conditions are defined according to behavioral
> ratings of a subject during scanning. So, in some sessions some
> conditions are missing. I tried to define onsets vector for absent
> conditions as empty, but this did not work (during estimation SPM
> pop-ups a window asking to fill the onsets for this condition).
> Obviously, I can omit the missing condition for this specific session,
> so that number of conditions in this session would be less than maximal.
> But this will require keeping track of which design column corresponds
> to which condition during contrast creation. Is this the only available
> solution?
>
> Thanks for the help,
> Vadim
--
Guillaume Flandin, PhD
Wellcome Trust Centre for Neuroimaging
University College London
12 Queen Square
London WC1N 3BG
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