Working for beverages without being thirsty: Human Pavlovian-instrumental transfer despite outcome devaluation

Abstract

The incentive-motivational salience acquired by a Pavlovian conditioned stimulus (CS) is reflected by its ability to strengthen the performance of a separately learned instrumental action exerted to obtain an outcome, a phenomenon known as Pavlovian-Instrumental transfer (PIT). By means of a PIT paradigm, the present study addressed whether the CS motivational properties vary dynamically with the value of the associated outcome. Previous studies on human PIT and outcome devaluation have provided mixed results, showing that in some cases post-training devaluation leaves PIT unaffected when outcomes are palatable foods or drugs, and when the devalued outcome is not consumed immediately. In Experiment 1, thirsty participants first learned to squeeze a rubber bulb to accumulate a beverage (plain water or sugary drink); then participants learned Pavlovian associations between cues and the beverage. When tested in extinction, a PIT effect emerged as expected. In Experiment 2, the PIT effect emerged even despite participants quenched their thirst before the test phase. Our results suggest that the incentive properties of a CS can surprisingly and irrationally endure the devaluation of the associated outcome even when plain water is used as reward, and thirst is quenched by immediate reward consumption. This result may provide important insights in the understanding of the psychological mechanisms underlying different types of addiction.