Delay Discounting

Delay discounting is often taken as a measure of impulsivity and of the ability to delay gratification. Specifically, delay discounting describes the process by which the value of an item is reduced as a function of the delay an individual has to wait until receiving that item (see Figure 1). Scenarios or tasks invoking delay discounting often will require the subject to make a choice between a small reward after a short delay, or a large reward after a long delay. Individuals are considered to have heightened delay discounting when they prefer the small, sooner reward over the large, later reward more than the average individual.

Heightened delay discounting is associated with certain behavioral pathologies, especially attention deficit hyperactivity disorder (ADHD) and substance abuse disorder.

Measures
There are a wide variety of delay discounting tasks. Often these are tailored to the species of interest. For example, for human subjects a verbal choice, often depicted on a computer screen, is given between two hypothetical secondary reinforcers: "Would you rather have $5 now or $10 in a month?" Contrarily, a rat often has to learn the lever pressing contingencies associated with "delayed" and "immediate" levers, and the rat is choosing between two extant primary reinforcers such as food pellets.

Delay discounting tasks can differ in more than their method of instruction/training and the type of reward delivered. For example, some delay discounting tasks offer a series of choices that are controlled by the experimenter, such as the Kirby task in humans and the within sessions task in animals. However, another popular variant adjusts some element of the task, such as delay or reward amount, according to the choices of the subject. Even within these groupings there are several variants, and there are numerous less frequently used variants that follow outside of these categories.