Secondary reinforcement in rats as a function of information value and reliability of the stimulus.

Abstract

Albino rats (N = 88, male) were trained to press a bar for food, then divided randomly into two groups and given 135 trials in the same Skinner boxes with bars removed,; two stimuli, when paired, ended together and always preceded food. For Group A, the second, shorter stimulus (So) was always redundant because the first stimulus (S1) had already given reliable information that food was coming. But for Group, B, S2 was informative, as for them S1 also occurred sometimes alone without food. After the training sessions, the bars were reinserted, bar pressing was retrained with food pellets, extinguished, and then retrained, this time using 1 sec. of one of the training stimuli as a secondary reinforcer in place of the food. The total of bar presses in 10 min. following the first secondary reinforcing stimulus was used as the measure of secondary reinforcing strength. The testing procedure was repeated after 48 hr. with other training stimulus as secondary reinforcer, so that all Ss were tested with both stimuli in a balanced sequence. Control experiments were run for baseline levels for pseudoconditioned and unconditioned rates of pressing, and for any activating effect of the stimuli. As predicted, S2 was a stronger secondary reinforcer when it was informative than when it was redundant; S1 was a more effective secondary reinforcer than S2 in that group for which S2 was a redundant predictor of primary reinforcement. In addition, S1 was a more effective secondary reinforcer when it had been a reliable predictor of food.