When is it worth waiting for? Food quantity, but not food quality, affects delay tolerance in tufted capuchin monkeys

Are capuchin monkeys (Sapajus spp.) sensitive to lost opportunities? The role of opportunity costs in intertemporal choice

Principles of economics predict that the costs associated with obtaining rewards can influence choice. When individuals face choices between a smaller, immediate option and a larger, later option, they often experience opportunity costs associated with waiting for delayed rewards because they must forego the opportunity to make other choices. We evaluated how reducing opportunity costs affects delay tolerance in capuchin monkeys. After choosing the larger option, in the High cost condition, subjects had to wait for the delay to expire, whereas in the Low cost different and Low cost same conditions, they could perform a new choice during the delay. To control for the effect of intake rate on choices, the Low cost same condition had the same intake rate ratio as the High cost condition. We found that capuchins attended both to intake rates and to opportunity costs. They chose the larger option more often in the Low cost different and Low cost same conditions than in the High cost condition, and more often in the Low cost different condition than in the Low cost same condition. Understanding how non-human primates represent and use costs in making decisions not only helps to develop theoretical frameworks to explain their choices but also addresses similarities with and differences from human decision-making. These outcomes provide insights into the origins of human economic behaviour. This article is part of the theme issue 'Existence and prevalence of economic behaviours among non-human primates'.

Delayed gratification in New Caledonian crows and young children: influence of reward type and visibility

Self-control underlies cognitive abilities such as decision making and future planning. Delay of gratification is a measure of self-control and involves obtaining a more valuable outcome in the future by tolerating a delay or investing a greater effort in the present. Contextual issues, such as reward visibility and type, may influence delayed gratification performance, although there has been limited comparative investigation between humans and other animals, particularly non-primate species. Here, we adapted an automated 'rotating tray' paradigm used previously with capuchin monkeys to test for delay of gratification ability that requires little pre-test training, where the subject must forgo an immediate, less preferred reward for a delayed, more preferred one. We tested New Caledonian crows and 3-5-year-old human children. We manipulated reward types to differ in quality or quantity (Experiments 1 and 2) as well as visibility (Experiment 2). In Experiments 1 and 2, both species performed better when the rewards varied in quality as opposed to quantity, though performed above chance in both conditions. In Experiment 1, both crows and children were able to delay gratification when both rewards were visible. In Experiment 2, 5-year-old children outperformed 3- and 4-year olds, though overall children still performed well, while the crows struggled when reward visibility was manipulated, a result which may relate to difficulties in tracking the experimenters' hands during baiting. We discuss these findings in relation to the role of contextual issues on self-control when making species comparisons and investigating the mechanisms of self-control.

Tolerance to delayed reward tasks in social and non-social contexts

Domestic dogs have demonstrated striking social skills towards humans, however, there are few studies investigating impulsivity with delay-choice tasks in communicative contexts. In Study 1 we introduced a novel social delay-choice task in which subjects had to choose between one human cueing an immediate, low quality reward and another human signaling a delayed, high quality reward. In Study 2 we evaluated the tolerance to increasing delays using social and non-social cues. We also explored if more self-controlled dogs show any distinct behaviours during delays. Finally, we correlated all results with the Dog Impulsivity Assessment Scale (Wright et al., 2011). In Study 1 dogs reached an average maximum delay of 11.55s. In Study 2 that average was 52.14s with social cues and 40.2s with non-social, but differences were not significant. Tolerance to delays showed high interindividual variation. Dogs remained mostly standing and near the delayed experimenter in the social tasks although we could not to find any distinct coping strategies. No significant correlations were found between the delay reached and behaviours, neither with the scale. These results show the relevance of the parameters and methods used to investigate tolerance to delay of reinforcements. More investigations are required, especially an assessment of the same subjects performing the same tasks using different contexts.

Impulsivity and sensitivity to amount and delay of reinforcement in an animal model of ADHD

Previous research has been inconclusive about the degree of impulsivity displayed by spontaneously hypertensive rats (SHR), an animal model of Attention Deficit Hyperactivity Disorder (ADHD). In the present set of experiments, concurrent-chains schedules were employed in order to explore SHR's impulsivity, sensitivity to delay, and sensitivity to amount of reinforcement; Wistar rats (WIS) were used as comparison group. In the three experiments - performed with different subjects - non-independent variable interval 30s schedules were presented in the initial links; the difference between experiments was in the terminal links. For exploring impulsivity, one of the terminal links (SS) was associated to a short delay (2s) and a small reinforcer (1 pellet), whereas the other terminal link (LL) was associated to a longer delay (28s) and a larger reinforcer (4 pellets). The results indicated a remarkably higher impulsivity in SHR. Because this impulsivity may have as potential mechanisms an increased sensitivity to delay and/or a decreased sensitivity to the amount of reinforcement, in experiments 2 and 3 these possibilities were examined. For assessing sensitivity to delay, the following pairs of fixed interval (FI) schedules were used in the terminal links in five conditions: 2-28, 6-24, 15-15, 24-6, 28-2s; the magnitude of reinforcement was 1 pellet in all conditions for both alternatives. For assessing sensitivity to amount, in five conditions the alternatives were associated with different magnitudes of reinforcement: 1-5 pellets, 2-4, 3-3, 4-2 and 5-1 in left-right alternatives, respectively; the delay to reinforcement was controlled by a FI 15s in all conditions and for both alternatives. The sensitivity to delay and the sensitivity to amount were calculated according to the Generalized Matching Law. The results indicated a higher sensitivity to delay in SHR, and the same sensitivity to amount in SHR and WIS rats. These results suggest that the increased sensitivity to delay influences the high level of impulsivity observed in SHR.