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:

> 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