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Yes. You are right. Assuming that conditions are constant in neural activity duration, modeling under 2s doesn't make much of a difference. However, as soon as you have variable condition durations, I believe you need to account for the differential durations. My point was more that, once you pass 2s, you need to model the duration even for constant duration events. With regard to (4), I just checked the most recent SPM release (r6906) and 0s is different from 0.0001s is different from 0.1s duration events, so there still seems to be some differences. Best Regards, Donald McLaren, PhD On Thu, Dec 1, 2016 at 12:04 PM, MRI More <[log in to unmask]> wrote: > Dear Donald, > > (1) only holds if you remain within conditions though. If mean RT is 300 > ms in one condition and 500 ms in another you will obtain different results > for the differential contrast depending on whether you go with a fixed > duration across conditions (be it 0 or 2 s or 400 ms) or the condition > means. > > With regard to (4), I could be wrong but I think this was adjusted in one > of the SPM12 updates this or last year. > > Best regards > > Helmut > >