Dear everyone,
I have excluded the first few volumes of an fMRI data series, but I would like to account for trials that were presented during this period, in other words, I would like to enter negative onsets. It seems that if they occur "too early", SPM treats the onset as if it were not present at all. I found this old message https://www.jiscmail.ac.uk/cgi-bin/webadmin?A2=SPM;4da16ab5.0908 and http://www.fil.ion.ucl.ac.uk/spm/software/spm2/improvements.html
"The option to perform a second-order or generalised convolution analysis using Volterra kernels is now assumed to be the same for all sessions. You can now also specify negative onset times up to 32 time bins (that default to 1/16 inter-scan intervals)."
In the meantime this seems to have been moved into spm_get_ons.m. I can adjust the lines in which ton is defined accordingly, i.e. 6001 instead of 33, but I'm not sure about two lines on sf, where 128 is added and not the otherwise 32 default time bins in one line, and 32 again in the one with comment % stimulus. I have also tried out a few values like 0, 32, 6000 and had the impression that this results in identical predictors.
Best
Helmut
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