Dear Dandil,
It seems you used TR units for "blue screen" (8 TRs of 2 s each), but accidentally seconds for "white screen" (duration = 16). If you want to specify the onsets and durations vectors in TR units, make sure you selected "Scans" as "Units for design" and use this unit consistently in your design matrix. Also don't forget that the first volume corresponds to the value 0, not 1. Assuming you excluded the first 4 s of rest (= 2 TRs) and then discarded three more volumes of "blue screen", correct vectors would be
onset=[0 17:20:195]
duration=[5 8 8 8 8 8 8 8 8 8 8]
onset=[7:20:195]
duration=8
But please double-check this yourself. In general I would suggest to go with seconds as a unit to avoid any confusion. Instead of throwing out the first few volumes afterwards you could already adjust the sequence parameters at the scanner. Typically there's some option to acquire several dummy scans (which are not saved) before the first trigger is sent to your stimulation computer. Concerning your design, you might want to think of some randomisation, so not always the order W B W B.
Hope this helps,
Helmut
|