function onset = getOnset(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).ons(%d)',1,session,1,condition,repetition);

onset = evalin('base',cmd);

end