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the difference between 0 duration and dur>0 is the function convolved with the hrf (stick for 0, boxcoar if >0). For all durations greater than 0, the duration specifies the magnitude, assuming a linear summation of activity. You should use 2 trs. -Michael On Tue, Mar 17, 2009 at 1:11 PM, Vadim Axel <[log in to unmask]> wrote: > Hi, > I have fast ER design, where each trial consists of 2 TRs. Some time ago it > was suggested here that I should define my duration as "2" (TRs). However, > I > am confused because in SPM help window it is written the follows: "Epoch > and > event-related responses are modeled in exactly the same way but by > specifying their different durations. Events are specified with a duration > of 0." Do they implicitly assume, that in ER design the event is always one > TR and I am OK, in my two_TRs_per_trial_case, with defining it as "2"? > Based > on this logic, defining "0" or "1" should in general be exactly the same? > > Thanks for help, > Vadim > -- Research Associate Gazzaley Lab Department of Neurology University of California, San Francisco