function radiobutton_function_cb(obj_name, handles)

switch obj_name
case 'first'
    turned_on = get(handles(1),'value');
    if turned_on
        set(handles(2), 'value', 0);
    end
case 'second'
    turned_on = get(handles(2),'value');
    if turned_on
        set(handles(1), 'value', 0);
    end
otherwise
    disp('not a valid callback...')
end