Mechanisms of impulsive choice: Experiments to explore and models to map the empirical terrain.

Impulsive choice is preference for a smaller-sooner (SS) outcome over a larger-later (LL) outcome when LL choices result in greater reinforcement maximization. Delay discounting is a model of impulsive choice that describes the decaying value of a reinforcer over time, with impulsive choice evident when the empirical choice-delay function is steep. Steep discounting is correlated with multiple diseases and disorders. Thus, understanding the processes underlying impulsive choice is a popular topic for investigation. Experimental research has explored the conditions that moderate impulsive choice, and quantitative models of impulsive choice have been developed that elegantly represent the underlying processes. This review spotlights experimental research in impulsive choice covering human and nonhuman animals across the domains of learning, motivation, and cognition. Contemporary models of delay discounting designed to explain the underlying mechanisms of impulsive choice are discussed. These models focus on potential candidate mechanisms, which include perception, delay and/or reinforcer sensitivity, reinforcement maximization, motivation, and cognitive systems. Although the models collectively explain multiple mechanistic phenomena, there are several cognitive processes, such as attention and working memory, that are overlooked. Future research and model development should focus on bridging the gap between quantitative models and empirical phenomena.

Narrative framing may increase human suboptimal choice behavior.

Under certain conditions, multiple nonhuman species have been observed engaging in choice behavior that resulted in less food earned when compared to the amount of food that was available to be earned over the course of a session. This phenomenon is particularly strong in pigeons, but has also been observed in rats and nonhuman primates. Conversely, human participants have demonstrated a propensity to choose more optimally. However, human participants do not exclusively choose the alternative associated with more reinforcement. Framing a task in a real-world narrative has been effective in improving problem-solving on other tasks such as the Wason Four-Card problem. The present study gave human participants a choice task with either abstract stimuli or with a real-world narrative. In addition, participants were given terminal stimuli that were either predictive or unpredictive of reinforcement. Thus, participants were assigned to one of four conditions: Abstract Predictive, Abstract Unpredictive, Narrative Predictive, or Narrative Unpredictive. In contrast to the improved performance on the Wason Four-Card task, the current study found no evidence that the addition of a real-world narrative improved optimal choice performance. Rather, it may have interfered with optimal choice selection in that participants who received the narrative and unpredictive terminal stimuli were at chance performance at the end of the experimental session. Conversely, participants in the Abstract Unpredictive, Abstract Predictive, and Narrative Predictive conditions all demonstrated a preference for the optimal alternative. Possible mechanisms for these findings and future directions are discussed.

Human Choice Predicted by Obtained Reinforcers, Not by Reinforcement Predictors.

Macphail (1985) proposed that "intelligence" should not vary across vertebrate species when contextual variables are accounted for. Focusing on research involving choice behavior, the propensity for choosing an option that produces stimuli that predict the presence or absence of reinforcement but that also results in less food over time can be examined. This choice preference has been found multiple times in pigeons (Stagner and Zentall, 2010; Zentall and Stagner, 2011; Laude et al., 2014) and has been likened to gambling behavior demonstrated by humans (Zentall, 2014, 2016). The present experiments used a similarly structured task to examine adult human preferences for reinforcement predictors and compared findings to choice behavior demonstrated by children (Lalli et al., 2000), monkeys (Smith et al., 2017; Smith and Beran, 2020), dogs (Jackson et al., 2020), rats (Chow et al., 2017; Cunningham and Shahan, 2019; Jackson et al., 2020), and pigeons (Roper and Zentall, 1999; Stagner and Zentall, 2010). In Experiment 1, adult human participants showed no preference for reinforcement predictors. Results from Experiment 2 suggest that not only were reinforcement predictors not preferred, but that perhaps reinforcement predictors had no effect at all on choice behavior. Results from Experiments 1 and 2 were further assessed using a generalized matching equation, the findings from which support that adult human choice behavior in the present research was largely determined by reinforcement history. Overall, the present results obtained from human adult participants are different than those found from pigeons in particular, suggesting that further examination of Macphail (1985) hypothesis is warranted.