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=Delayed Gratification=

Overview: Delayed Gratification in Animals
Delayed gratification or deferred gratification, the ability to wait for something you would like, is an animal behavior that can be linked to delay discounting, ecological factors, individual fitness, and neurobiological mechanisms. Research for this behavior has been conducted with animals such as capuchin monkeys, tamarins, marmosets, rats, and pigeons.

Delay Discounting
When animals are faced with a choice to either wait for a reward, or receive a reward right away, the discounting of the reward is hyperbolic. As the length of time of waiting for a reward increases, the reward is discounted at a gradual rate. Empirical data have suggested that exponential discounting, rewards discounting at a constant rate per unit of waiting time, only occurs when there are random interruptions in foraging.

Discounting can also be related to the risk sensitivity of animals. Rather than relating risk to delay, risk sensitivity acts as a function of delay discounting. In a study conducted by Haden and Platt, macaque monkeys were given the choice of a medium reward that they knew they would receive, versus a more risky choice. The riskier choice would reward the monkey with a large reward fifty percent of the time, and a small reward the other fifty percent. The ultimate payoff was the same, but the monkeys preferred the riskier choice. They speculated that the monkeys did not see their action as risky, but rather as a large, delayed reward. They reasoned that the monkeys viewed the large reward as certain: if they did not get the large reward the first time around, they would eventually get it, but at a longer delay.

To test for this theory, they gave the same test while varying the time between the opportunities to choose a reward. They found that as the interval increased, the number of times that the monkeys chose the more risky reward decreased. While this occurred in macaque monkeys, the varying interval time did not affect pigeons’ choices in another study. This suggests that research looking into varying risk sensitivity of different species is needed.

When provided a choice between a small, short delay reward, and a large, long delay reward, there is an impulsive preference for the former. Additionally, as the delay time for the small/short and large/long reward increases, there is a shift in preference for the larger reward. This evidence only supports hyperbolic discounting, not exponential.

Ecological Factors
Although predicting reward preference seems simple when using empirical models, there are a number of ecological factors that seem to affect the delayed gratification behavior of animals. In real world situations, “discounting makes sense because of the inherent uncertainty of future payoffs,”.

One study looked at how reward discounting is context specific. By differing the time and space between small and large rewards, they were able to test how these factors affected the decision making in tamarins and marmosets. They showed that tamarins will travel longer distances for larger food rewards, but will not wait as long as marmosets. Conversely, marmosets will wait longer, but will not travel as far. They then concluded that this discounting behavior directly correlates to the normal feeding behavior of species. The tamarins feed over large distances, looking for insects. Capturing and eating insects requires a quick and impulsive decision and action. The marmosets, on the other hand, eat tree sap, which takes more time to secrete, but does not require that the marmosets to cover large distances.

Delayed Gratification and Individual Fitness
There are costs and risks that are associated with delaying gratification behavior. One such cost is the basic opportunity cost associated with time spent waiting. While waiting, individuals lose time that could be used to find other food. There are also two risks associated with being patient. First, there is a risk that a conspecific might get to the food first, also known as an interruption risk. Second, there is the risk that the chance to get the reward will be cut short, perhaps by a predator, also known as a termination risk. These costs and risks create situations in which the fitness of the individual is threatened.

There are several examples that show how reward delay occurs in the real world. For example, animals that eat fruit have the option of eating unripe fruit right away, or waiting, delaying gratification, until it becomes ripe. The interruption risk plays a part here, because if the individual forgoes the unripe fruit, there is a chance that another individual may come along and get to it first. Also, in extractive foraging, such as with nuts and shellfish, the outer shell creates a delay.

Neurobiological Mechanisms
There are several neurobiological studies that address the mechanisms involved with processing reward delays. It has been suggested that there are specific sections of the brain that process this information. These sections may be “modulated by the balance of the neurotransmitters dopamine and serotonin,”. The physiological similarities between animals and humans have led to more comparative research between the two groups.