Hi SPMers,
I am wondering whether any one has had some experience with including ‘a
button press’ as a covariate in the SPM analysis.
I have an event related design with 3 conditions intermixed. In order to
monitor participants’ vigilance I included an additional stimulus which,
when seen, required a participant to press a button. This happened on 10%
of trials. I would like to include ‘a button press’ as a covariate into the
SPM Matrix in the same way that one normally includes the motion parameters
as covariates, to discard any activation due to these nuisance variables.
I have acquired 404 volumes and my design matrix (for the first level
analysis) has 404 rows. I also had 404 rows of 6-motion parameters and
therefore it was very straightforward to enter them into the design matrix.
In contrast, I have only 30 ‘button presses’ per 404 scans per participant.
I would be very grateful for any advice on how to include the ‘button
press’ as regressor into the analysis. I am assuming that this has to be
done on the 1st level analysis.
Thank you very much for your help. Best wishes,
Agnieszka
University of Aston, UK
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