Dear experts, I'd like to use optseq2 to optimize the order of events as well as inter stimulus intervals. My experiment contains 3 runs and each run contains 3 events, say Cp, Cn and Pobe events Each stimulu will be presented 4, 4 and 1 sec and the numbers of times that each event type will be presented during the course of the run are 12 12 and 4 respectively, and interstimulus interval ranges from 8–12 sec. So each run would last around 380 sec. I used the following code: optseq2 --ntp 380 --tr 1 --psdwin 0 20 1 --ev Cp 4 12 --ev Cn 4 12 --ev Prob 1 3 --evc 1 -1 0 --tnullmin 8 --tnullmax 12 --nkeep 3 --o IAPS --nsearch 10000 However, the durations of some NULL events were more than 12 sec and the last NULL events were more than 30 sec. Did I use optseq2 in the right way? How could I fix it? Thanks in advance & Best regards, Feng Zhou