Evidence for motivational enhancement of sign-tracking behavior under reward uncertainty

Reward uncertainty has been shown to invigorate rather than attenuate cue attraction and responding. For example, a number of findings have shown that partial reinforcement in autoshaping increases response rates to a conditioned stimulus (conditional stimulus) in comparison with continuous reinforcement. However, identifying the nature of this effect remains a topical question. The frustration theory posits that animals are frustrated by reward loss and predicts that enhanced responding results from higher response rates to conditional stimulus presentations that follow nonrewarded trials rather than rewarded trials. In contrast, the incentive hope hypothesis suggests that animals are motivated by possible future rewards and predicts similar response rates after rewarded and nonrewarded trials. Our results, which consist of a reanalysis of previously published data (Hellberg, Levit, & Robinson, 2018), are consistent with the incentive hope hypothesis because no differences were found between trials that follow rewarded or nonrewarded trials, or between trials that follow small or larger amounts of food reward in rats. There was also no evidence for an accumulation of frustration across each training session, with rats instead displaying enhanced yet stable responding from beginning to end. The incentive hope hypothesis is also briefly discussed in relation to the concept of incentive salience. (PsycINFO Database Record (c) 2019 APA, all rights reserved).