function duration = getDuration(session, condition, repetition)
%session    : the session number. 
%condition  : the condition intrested in (CUE1,CUE2,...)
%repetition : the repetition number; same event, different time ;)

cmd = sprintf('SPM.Sess(%d,%d).U(%d,%d).dur(%d)',1,session,1,condition,repetition);

duration = evalin('base',cmd);

end