Within-event learning contributes to value transfer in simultaneous instrumental discriminations by pigeons

Abstract

Following simultaneous discrimination training with pigeons, in which responding to the S+ was reinforced on half of the trials and responding to the S- was never reinforced, we examined the effect on the S- of presenting the S+ by itself and the effect on the S+ of presenting the S- by itself (relative to an S- or an S+ for which there had been no single-stimulus presentations). For Group A+, responding to the S+ presented by itself was always reinforced, whereas for Group A-, such responding was extinguished. For Group B+, responding to the S- presented by itself was always reinforced, whereas for Group B-, responding was extinguished. Although both Group A+ and Group A- tended to avoid their associated S- (relative to a control S-), Group A+ avoided its associated S- less than did Group A-. In contrast, although for Group B+, presentation of the S- alone increased the pigeons' preference for its associated S+ (relative to a control S+), for Group B-, presentation of the S- alone had little effect on its preference for its associated S+. These results suggest that presentation of one stimulus from a simultaneous discrimination has two independent and sometimes opposite effects on the other discriminative stimulus. First, it reduces the strength of within-event conditioning between the S+ and the S-, and second, if the value of the singly presented stimulus has increased, some of its newly acquired value will transfer retroactively to the stimulus with which it was originally paired.