The effect of informational stimuli on instrumental response rate: Signalling reward versus signalling the availability of reward

Rats were trained to press a lever for food on an interval schedule and were given a brief cue (0.5 sec) between the operative response and the reward (C condition). Some control subjects in Experiments 1, 2 and 4 were given their cue either following the end of the temporal interval during which reward had been unavailable (SD condition), or randomly with respect to food (R condition). Other control subjects in Experiments 2 and 4 received both the food-correlated cue and the temporal-interval stimulus (B condition). In all experiments, rate of responding was lowest for the C subjects and for B animals when the two cues were from different modalities. Food-correlated and temporal-interval cues did not interact, suggesting that a reward-correlated signal does not affect response rate simply by enhancing the salience of the temporal interval offset.