Instrumental performance following reinforcer devaluation depends upon incentive learning

Conditioning an aversion to the reinforcer following instrumental training reduces performance in a subsequent extinction test. Three experiments examined whether this reinforcer-devaluation effect depends upon experience with the devalued reinforcer prior to the extinction test. In Experiments 1 and 2 thirsty rats were trained to press a lever for sucrose solution in a single session. All animals then received an injection of lithium chloride (LiCl) either immediately following the session or after a delay of 6 hr. On the next day either the sucrose solution or water was presented non-contingently either in the operant chamber without the lever present or in a separate drinking cage. In a subsequent extinction test only the animals that had received immediate LiCl and re-exposure to non-contingent sucrose pressed less than those in the delayed-LiCl control groups. Experiment 3 demonstrated that this difference depended, at least in part, on post-conditioning exposure to a contingent reinforcer. Lever pressing and chain pulling were reinforced concurrently with either a sucrose or a sodium chloride solution in a single session immediately before the administration of LiCl. All animals then received non-contingent presentations of one of the reinforcers in the absence of both manipulanda. Finally, performance of both actions was assessed in an extinction test. Re-exposure to a reinforcer produced a relative reduction in the performance of its associated action on test. These results are interpreted as evidence that the instrumental reinforcer devaluation effect depends upon a process of incentive learning.     

Incentive learning following reinforcer devaluation is not conditional upon the motivational state during re-exposure

Three experiments analysed the effect of re-exposure to the reinforcer following aversion conditioning on instrumental performance. In the first experiment, groups of hungry and thirsty rats were trained to press a lever for sucrose, which was then followed by a single injection of lithium chloride (LiCl). On the following day, half the animals in each motivational condition received re-exposure to the sucrose solution; the remaining animals were not re-exposed. In a subsequent extinction test animals that had received re-exposure to the sucrose pressed less than animals that were not re-exposed. Moreover, the effect of re-exposure to the sucrose solution was similar following training under hunger and thirst. In the remaining studies, animals were trained to lever-press for sucrose while either hungry or thirsty. They were then injected with LiCl and re-exposed to the sucrose while either hungry or thirsty, i.e. in the same or different motivational state employed during training, or they were not re-exposed. Lever pressing was then tested in extinction in the training motivational state. As in the first experiment, re-exposure to the reinforcer after aversion conditioning enhanced the magnitude of the reinforcer devaluation effect. More importantly, re-exposure to the sucrose produced a comparable effect on instrumental performance, whether re-exposure was given under the same or different motivational state to that employed during training. These results suggest that the instrumental reinforcer devaluation effect depends upon a process of incentive learning, but that this process is not conditional upon the current motivational state of the animal.     

THE INFERIORITY CURRICULUM

Bernard looks back at the last decade and notes that although many things have improved, women at all levels in academia still face more subtle forms of discrimination, which comprise what she calls the Inferiority Curriculum. Exposure of these subtle discriminatory behaviors is gradually occurring through what Bernard has termed the Feminist Enlightenment, a discipline-by-discipline process which began in the mid-1960s. Bernard documents many down-putting behaviors that continue to undermine women's achievement and argues the necessity of overcoming the damage by building positive self-images among women.     

Asymmetrical interactions between thirst and hunger in pavlovian-instrumental transfer

Pavlovian-instrumental transfer experiments have demonstrated that a stimulus paired with a sucrose solution under hunger will increase instrumental performance under thirst relative to a stimulus previously paired with food pellets. In Experiment 1 it was demonstrated that this difference is, in part, produced by suppression induced by the pellet stimulus, which, it was found, acted to reduce instrumental performance under thirst. In Experiment 2, the reverse shift was examined, comparing the effects of stimuli paired with either a saline solution or a sucrose solution under thirst on instrumental performance under hunger. Although the sucrose stimulus was found to elevate performance when hungry, the saline stimulus was found to be without effect. This asymmetry in the interaction between hunger and thirst is discussed in terms of the way motivational states control the interaction between sensory and affective components of the reinforcer.     

Instrumental Outcome Devaluation Is Attenuated by the Anti-emetic Ondansetron

In three experiments we assessed the effect of an anti-emetic, the selective S-HT antagonist ondansetron, on (1) the conditioning of a taste aversion using lithium chloride (LiCl); (2) the expression of that aversion; and (3) instrumental outcome-devaluation effects. In Experiment 1 it was found that ondansetron reduced the aversion induced by LiCl when administered prior to the LiCl injection and also attenuated the expression of that aversion when administered prior to test sessions. In Experiments 2 and 3, thirsty rats were trained, in a single session, to lever press and chain pull for sucrose and saline solutions concurrently before being injected with LiCl. They were then re-exposed to both solutions, one after injection of vehicle and the other after injection of ondansetron. In a choice extinction test on the levers and chains, animals performed more of the action whose training outcome was re-exposed under ondansetron than the other action, whether the test was conducted after an injection of vehicle or after one of ondansetron.