Sorry for posting this message again, but I got an email that said my last message failed to be posted and sent. Before I sent this message last time, I had searched the whole lists for all messages with "derivatives" in subjects but none of them could answer my following questions. BTW, in the past, after posting a message, I got a confirming email in one or two minutes; but last time, I got that after 3 hours. Was that due to system change or system problem? Anyway, thanks!
For removing the problem that different slices were acquired at different time, I tried to use time and dispersion derivatives instead of traditional slicetiming (my TR = 2s).
I'm now wondering: if I do that, can I still compare PSTH (peri-stimulus histograms) of two regressors / two voxels (like the bottom part of figure 29.14 in p.240 in SPM8 manual)? (If no, what is the appropriate alternative way?) As we know, the time derivatives are different for different voxels and regressors. So PSTH for bf1 of each regressor or voxel is in fact shifted forward or backward in different time length. So when we compare PSTH for bf1 of two regressors or two voxels, even if the peak of regressor / voxel A appears earlier than that of regressor / voxel B, we don't know whether it is really so or it is just caused by the different time derivatives.
Another related question is: can we integrate dispersion derivative into PSTH? If yes, how? If no, what is the appropriate alternative way?
Looking forward to your help.
Thank you in advance,
James
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