Dear Guillaume,
Thank you for your feedback. I like very much your suggestion of using the informed basis set by default and modifying the design matrix to use a
FIR model for some selected conditions. The possibility to use different convolution basis sets for different conditions with SPM is something that I have been looking for from the beginning, and I am happy to hear that a workaround to make this possible exists.
However, after having looked at the code in spm_graph, I'm affraid that I don't quite understand how to implement this in practice. Could you elaborate on how to replace some selected conditions in a already existing design matrix by FIR model subpartitions (X) using this code?
I also have two additional questions:
1) I have read that the time-period for which SPM estimates the PSTH using FIR is 32s by default (as defined by the value 32 in xBF.order in spm_graph). Is this indeed the case, and if so, what would be the implications when using a window length (and order) that exceed this value?
2) From having a look at my design matrix acquired by using the FIR basis set only, I see that the FIR events are coded by a value of 16 in each bin which seems to correspond to my microtime onset. Is this to be expected?
Thanks a lot for your help.
Kind regards,
Jelle
|