Reward Contrast Effects on Impulsive Choice and Timing in Rats

Abstract

Despite considerable interest in impulsive choice as a predictor of a variety of maladaptive behaviors, the mechanisms that drive choice behavior are still poorly understood. The present study sought to examine the influence of one understudied variable, reward magnitude contrast, on choice and timing behavior as changes in magnitude commonly occur within choice procedures. In addition, assessments of indirect effects on choice behavior through magnitude-timing interactions were assessed by measuring timing within the choice task. Rats were exposed to choice procedures composed of different pairs of magnitudes of rewards for either the smaller-sooner (SS) or larger-later (LL) option. In Phase 2, the magnitude of reward either increased or decreased by 1 pellet in different groups (LL increase = 1v1→1v2; SS decrease = 2v2 → 1v2; SS increase = 1v2 → 2v2), followed by a return to baseline in Phase 3. Choice behavior was affected by the initial magnitudes experienced in the task, demonstrating a strong anchor effect. The nature of the change in magnitude affected choice behavior as well. Timing behavior was also affected by the reward contrast manipulation albeit to a lesser degree and the timing and choice effects were correlated. The results suggest that models of choice behavior should incorporate reinforcement history, reward contrast elements, and magnitude-timing interactions, but that direct effects of reward contrast on choice should be given more weight than the indirect reward-timing interactions. A better understanding of the factors that contribute to choice behavior could supply key insights into this important individual differences variable.

Mechanisms of impulsive choice: II. Time-based interventions to improve self-control

“…The combined results are consistent with impulsive choice serving as a trait variable in rats, similar to what has been observed in humans (Jimura et al 2011; Kirby 2009; Odum 2011b; Odum and Baumann 2010; Simpson and Vuchinich 2000). The results are also consistent with a recent study examining stability of impulsive choice in rats over multiple assessments (Broos et al 2012) and with recent research in our laboratory examining test-retest stability over periods of 2–3 weeks (Smith et al in preparation) and up to 5 months (Peterson et al under review). In all of these cases, there were no significant migrations in choice behavior over repeated testing, suggesting that the current results were not due to these factors.…”

Durability and generalizability of time-based intervention effects on impulsive choice in rats

“…Another factor that could have affected the results is within-task order effects. All task manipulations were conducted in an ascending order, which could have resulted in anchoring effects to the initial parameters (Smith, Peterson, and Kirkpatrick 2016). At a minimum, this could have impacted on the slope and intercept estimates from the regression models.…”

Dietary effects on the determinants of food choice: Impulsive choice, discrimination, incentive motivation, preference, and liking in male rats

“…While Group HF and HS appear to produce similar results across tasks, Group C did not display a strong preference for either reward during the delay manipulation yet displayed a preference for the SS reward during the magnitude manipulation. The results could potentially be due to a magnitude contrast effect in the chow condition (Smith, Peterson, & Kirkpatrick, 2016), or possibly to the effect of previous experience on the delay task. Further study will be required to discern the nature of these effects in the chow group.…”