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.


On Tue, Mar 17, 2009 at 1:11 PM, Vadim Axel <[log in to unmask]> wrote:
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,

Research Associate
Gazzaley Lab
Department of Neurology
University of California, San Francisco