opon = stim(:,1); opoff = stim(:,2); % stim on off times
scn = stim(:,3); % number of stim wavelengths
sint = stim(:,4); % stim intensity for each epoch
ilvl = unique(sint); % unique stim intensitites
inum = length(ilvl); % number of different stim intensitites

ontim = cell(1,inum); offtim = ontim; opfr = ontim;
for oi = 1:inum
    curint = ilvl(oi);
    curidx = find(sint == curint);
    ontim{oi} = opon(curidx); offtim{oi} = opoff(curidx);
    for oti = 1:length(curidx)
        optmp = (ontim{oi}(oti)*3):(offtim{oi}(oti)*3);
        opfr{oi} = [opfr{oi} optmp];
    end
end