Choice of a warning signal or none in several unavoidable-shock situations

In a two-compartment grid shuttle box, rats tended to prefer a 1/2 sec. or a 5 sec. warning signal over no signal preceding unavoidable shock. They did not prefer either a 0 sec. or random signal-shock interval over no signal. And they did not tolerate more shock to obtain a signal than they had to tolerate in a no-signal compartment.