Steep delay discounting is characterized by a preference for small immediate outcomes relative to larger delayed outcomes and is predictive of drug abuse, risky sexual behaviors, and other maladaptive behaviors. Nancy M. Petry was a pioneer in delay discounting research who demonstrated that people discount delayed monetary gains less steeply than they discount substances with abuse liability. Subsequent research found steep discounting for not only drugs, but other nonmonetary outcomes such as food, sex, and health. In this systematic review, we evaluate the hypotheses proposed to explain differences in discounting as a function of the type of outcome and explore the trait-and state-like nature of delay discounting. We found overwhelming evidence for the state-like quality of delay discounting: Consistent with Petry and others' work, nonmonetary outcomes are discounted more steeply than monetary outcomes. We propose two hypotheses that together may account for this effect: Decreasing Future Preference and Decreasing Future Worth. We also found clear evidence that delay discounting has trait-like qualities: People who steeply discount monetary outcomes steeply discount nonmonetary outcomes as well. The implication is that changing delay discounting for one outcome could change discounting for other outcomes.
The present study examined persistence and relapse of reinforced behavioral variability in pigeons. Pigeons emitted four‐response sequences across two keys. Sequences produced food according to a lag schedule, in which a response sequence was followed by food if it differed from a certain number of previous sequences. In Experiment 1, food was delivered for sequences that satisfied a lag schedule in both components of a multiple schedule. When reinforcement was removed for one component (i.e., extinction), levels of behavioral variability decreased for only that component. In Experiment 2, food was delivered for sequences satisfying a lag schedule in one component of a multiple schedule. In the other component, food was delivered at the same rate, but without the lag variability requirement (i.e., yoked). Following extinction, levels of behavioral variability returned to baseline for both components after response‐independent food delivery (i.e., reinstatement). In Experiment 3, one group of pigeons responded on a lag variability schedule, and the other group responded on a lag repetition schedule. For both groups, levels of behavioral variability increased when alternative reinforcement was suspended (i.e., resurgence). In each experiment, we observed some evidence for extinction‐induced response variability and for variability as an operant dimension of behavior.
Delay discounting refers to a decline in the value of a reward when it is delayed relative to when it is immediately available. Delay discounting tasks are used to identify indifference points, which reflect equal preference for two dichotomous reward alternatives differing in both delay and magnitude. Indifference points are key to assessing delay discounting because they allow us to quantify the degree to which delay impacts value for a given individual. For example, if at a 1 week delay and a maximum of $1000, the indifference point is at $700 we know that, for that participant, a 1-week delay corresponds to a 30% reduction in value. This video outlines an adjusting amount delay discounting task that identifies indifference points relatively quickly and is inexpensive and easy to administer. Once data have been collected, non-linear regression techniques are typically used to generate discounting curves. The steepness of the discounting curve reflects the degree of impulsive choice of a group or individual. These techniques have been used with a wide range of commodities and have identified populations that are relatively impulsive. For example, people with substance abuse problems discount delayed rewards more steeply than control participants. While degree of discounting varies as a function of the commodity examined, discounting of one commodity correlates with discounting of other commodities, which suggests that discounting may be a trait-like variable1.
We examined the effects of outcome framing on delay discounting. In Experiment 1, participants completed four delay-discounting tasks. In one monetary task, money was framed in units of dollars ($50), and in the other, money was framed in units of handfuls of quarters (equal to $50). In one food task, food was framed in clear units of food (e.g., 100 M&Ms), and in the other, food was framed in units of servings (e.g., 10 servings of M&Ms). When money was framed in units of dollars, participants discounted less by delay compared to discounting of handfuls of quarters. When food was framed as clear units, participants also discounted less compared to how they discounted servings. In Experiment 2, participants completed two delay-discounting tasks for dollars and quarters (e.g., $50 or 200 quarters) to determine if the results of Experiment 1 were due to the differences in handling costs. In one delay-discounting task, money was framed in units of dollars. In the other delay-discounting task, money was framed in units of quarters. There was no difference in how participants discounted delayed money framed as dollars or quarters. Clear unit framing may result in less discounting by delay than fuzzy unit framing.
There is disagreement about how to characterize the environment-behavior relations involved in the reinforcement of behavioral variability. The present research examined some of these issues using food-maintained, 4-peck sequences in pigeons. Experiment 1 evaluated the claim that behavioral variability is not reinforced directly but, rather, is the byproduct of changing over within sequences. Considerably higher levels of behavioral variation occurred under a relative-frequency threshold contingency than under a contingency that required a changeover but not variability per se. These results are consistent with the argument that behavioral variability is reinforced directly. Experiment 2 assessed the effects on variation levels of manipulating inter-trial and inter-response intervals. Variability increased with longer inter-response intervals but not with longer inter-trial intervals. These results are consistent with multiple explanations, including the notion that remembering past behavior interferes with the emission of reinforced variation. Consequently, Experiment 3 examined more directly the relation between remembering and reinforced variation. Variation levels were not affected by a concurrent contingency that encouraged pigeons to remember their past behavior. The implications of this research are presented in the context of working towards an understanding of the environment-behavior relations involved in the reinforcement of behavioral variability.
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