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Token exchange inherently introduces an element of delay between behavior and reward and so token studies may help us better understand delay of gratification and self-control. To examine this possibility, we presented three language-trained chimpanzees with repeated choices involving different foods that could be eaten immediately or lexigram (graphic symbol) tokens that represented (and could be traded for) foods later. When both options were foods, chimpanzees always chose more preferred foods over less preferred foods. When both options were lexigram tokens representing those same foods, performance remained the same as chimpanzees selected the higher value token and then traded it for food. Then, when faced with choosing a token that could be traded later or choosing a food item that could be eaten immediately, most chimpanzees learned to make whatever response led to the more preferred food. They did this even when that meant selecting a high value lexigram token that could be traded only 2 to 3 min later instead of a medium value, but immediately available, food item. Thus, chimpanzees flexibly selected tokens even though such selections necessarily delayed gratification and required forgoing immediately available food. This finding illustrates the utility of symbolic token exchange for assessing self-control in nonhuman animals. Am. J. Primatol. 74:864-870, 2012. © 2012 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

Abstract: We tested four chimpanzees in a self-control task in which food rewards accumulated as long as they were not eaten. In one condition, the chimpanzees had to perform a computer task that directly led to the delivery of the food rewards. In another condition, working on the computerized task was not required and any such work was not linked to the delivery of rewards. The third condition offered no computerized task (chimpanzees simply waited for food rewards to be delivered). Three of four chimpanzees showed no effect of the work scenario on delay of gratification. The one chimpanzee that showed an influence of work scenario on self-control was the overall poorest performing animal. This animal delayed gratification the longest, however, when work was required and reward delivery was directly linked to that work. Therefore, although there is little evidence linking delay of gratification to work requirements in chimpanzees, chimpanzees with lower overall self-control might benefit from having some work available if reward accumulation is contingent on performing that work. [Copyright &y& Elsevier]

Abstract: The variables of delay and effort have been found to influence self-control predictably and in similar fashion when tested independently, but it is unclear how they influence self-control interactively. In the present study, I tested these two variables simultaneously to gain better understanding of their combined influence on self-control. A computerized task was employed in which monkey participants could sequence 1 or more digital images before “cashing-out,” after which they would receive their accumulated rewards. Delay was manipulated by adjusting the speed of the cursor used to select images. Cognitive effort was manipulated by presenting image sets that appeared in either a constant or a randomized configuration. For most monkeys, an interaction was found between the effects of delay and effort on the number of images selected before cashing-out. The results suggest that, when combined, these two variables have a complex influence on self-control. [Copyright &y& Elsevier]

The authors tested the self-control of rhesus macaques by assessing if they could refrain from reaching into a food container to maximize the accumulation of sequentially delivered food items (a delay-maintenance task). Three different versions of the task varied the quantity and quality of available food items. In the first 2 versions, food items accumulated across the length of the trial until a monkey consumed the items. In the 3rd task, a single less-preferred food item preceded a single more-preferred food item. Some monkeys delayed gratification even with relatively long delays between deliveries of items. However, the data suggested that self-control, in the majority of tested individuals, was not significantly different across different task versions and that self-control by macaques was not as prevalent in these tasks as it is in chimpanzees and human children. [ABSTRACT FROM AUTHOR]

Abstract: Previous research in our laboratory has demonstrated that chimpanzees can delay gratification by inhibiting consumption of available food items for as long as 3min as an experimenter transfers additional food items from a transparent container to a bowl placed in front of the subject. In this study, we examined the influence of the visibility of the food source, as well as the presence of the experimenter, on four chimpanzees’ self-control in this paradigm. In Experiment 1 an experimenter transferred 15 preferred food items between a distant opaque container and a bowl placed in front of the subject. In Experiment 2 we tested the chimpanzees with an automated system that (in the absence of the experimenter) transferred up to 36 highly preferred food items from a universal food dispenser to a container located either inside or outside of the subject''s enclosure. There were no differences in self-directed behaviors or attentiveness to the food items between the self-imposed and externally imposed delay conditions. A final experiment with the automated paradigm indicated that individuals could delay gratification for up to 11min in order to obtain all 36 food items. [Copyright &y& Elsevier]

There is considerable evidence indicating that chimpanzees can delay gratification for extended time intervals, particularly in the accumulation task in which food items accumulate within a participant's reach until the participant begins to consume them. However, there is limited evidence that other ape species might also exhibit this capacity, despite there being a number of similar studies indicating that nonape species (e.g., monkeys and birds) can delay gratification, but not for nearly as long as chimpanzees. To help define the taxonomic distribution of delay of gratification behavior in the order Primates, we tested 6 orangutans in the current experiments and compared their performance with comparable data from a previous study with capuchin monkeys. We varied delay length and visibility of the items that were still available for accumulation to determine the impact of these factors on performance. Species differences on the accumulation task emerged when comparing the current data to data from a previous study. Orangutans outperformed capuchin monkeys, suggesting that ape species may generally show better delay of gratification and delay maintenance abilities than monkeys. However, more studies are necessary to rule out alternative hypotheses on the distribution of delay maintenance abilities across primate species. [ABSTRACT FROM AUTHOR]

Delaying gratification involves 2 components: (1) delay choice (selecting a delayed reward over an immediate one) and (2) delay maintenance (sustaining the decision to delay gratification even if the immediate reward is available during the delay). Two tasks most commonly have explored these components in primates: the intertemporal choice task and the accumulation task. It is unclear whether these tasks provide equivalent measures of delay of gratification. Here, we compared the performance on the intertemporal choice task and the accumulation task of capuchin monkeys (Cebus apella) belonging to 2 study populations. We found only limited evidence of a significant correlation in performance. Consequently, in contrast to what is often assumed, our data provide only partial support for the hypothesis that these tasks provide equivalent measures of delay of gratification. [ABSTRACT FROM AUTHOR]