Trading up: chimpanzees (Pan troglodytes) show self-control through their exchange behavior

Abstract

Self-control is defined as the ability or capacity to obtain an objectively more valuable outcome rather than an objectively less valuable outcome though tolerating a longer delay or a greater effort requirement (or both) in obtaining that more valuable outcome. A number of tests have been devised to assess self-control in nonhuman animals, including exchange tasks. In this study, three chimpanzees (Pan troglodytes) participated in a delay of gratification task that required food exchange as the behavioral response that reflected self-control. The chimpanzees were offered opportunities to inhibit eating and instead exchange a currently possessed food item for a different (and sometimes better) item, often needing to exchange several food items before obtaining the highest-valued reward. We manipulated reward type, reward size, reward visibility, delay to exchange, and location of the highest-valued reward in the sequence of exchange events to compare performance within the same individuals. The chimpanzees successfully traded until obtaining the best item in most cases, although there were individual differences among participants in some variations of the test. These results support the idea that self-control is robust in chimpanzees even in contexts in which they perhaps anticipate future rewards and sustain delay of gratification until they can obtain the ultimately most-valuable item.

Chimpanzees can point to smaller amounts of food to accumulate larger amounts but they still fail the reverse-reward contingency task.

“…The chimpanzees voluntarily separated from one another for the current test sessions, but remained in constant visual and auditory access to one another during testing. These chimpanzees had participated in a wide range of cognitive-behavioral testing, including tests of self-control that require delay of gratification (e.g., Beran, 2002; Beran & Evans, 2006; Beran et al, 2016; Beran, Savage-Rumbaugh, Pate, & Rumbaugh, 1999; Evans & Beran, 2007; Parrish et al, 2013). …”

“…Chimpanzees have excelled in the accumulation task across extended delay periods (up to 11 minutes), when food items were not visible to the animals, in the absence of an experimenter (Beran & Evans, 2006), and even in the face of sustained effort (Beran & Evans, 2009) or when coordination with a social partner was required to facilitate reward delivery (Parrish, Perdue, Evans, & Beran, 2013). Chimpanzees also demonstrate impressive levels of self-control in other paradigms, including food-exchange tasks that require subjects to trade a food item in their possession for a potentially higher-valued reward (e.g., Beran, Rossettie, & Parrish, 2016; Dufour, Pelé, Sterk, & Thierry, 2007). …”

Self-control assessments of capuchin monkeys with the rotating tray task and the accumulation task

“…In that case, choice of the larger-later option means animals are then committed to waiting out the delay interval (e.g., Ainslie, 1974; Berns, Laibson, and Lowenstein, 2007; Logue, 1988; Tobin, Chelonis, and Logue, 1993; Tobin, Logue, Chelonis, Ackerman, and May, 1996; Rachlin and Green, 1972; Stevens, Hallinan, and Hauser, 2005; Stevens and Mühlhoff, 2012). Other tasks require animals to avoid immediate rewards for the sake of obtaining later, better ones, either through movements through space where the less preferred item is encountered first (e.g., Evans and Westergaard, 2006; Stevens, Rosati, Ross, and Hauser, 2005) or by keeping a lower preference item (rather than consuming it) through a delay in order to exchange it for a more preferred item at a later time (e.g., Beran, Rossettie, and Parrish, 2016; Dufour, Pelé, Sterck, and Thierry, 2007; Judge and Essler, 2013; Pelé, Dufour, Micheletta, and Thierry, 2010; Pelé, Micheletta, Uhlrich, Thierry, and Dufour, 2011; Ramseyer, Pelé, Dufour, Chauvin, and Thierry, 2006). In these tasks, subjects must avoid taking the less preferred but more immediate reward, which is always present and (presumably) always a temptation, so as to later obtain the better reward (e.g., Beran, Savage-Rumbaugh, Pate, and Rumbaugh, 1999; Grosch and Neuringer, 1981).…”

Chimpanzee food preferences, associative learning, and the origins of cooking

“…This trading behavior is well-established with chimpanzees in a variety of other self-control tests in which delayed rewards are obtained that are better than immediate ones (e.g., Beran, Rossettie, & Parrish, in press; Dufour, Pele, Sterck, & Thierry, 2007). Furthermore, chimpanzees and other great apes will allow food quantities to continue to grow when delaying eating those items continues the accumulation (Beran 2002; Beran & Evans, 2006; Evans & Beran, 2007; Parrish et al, 2014; Stevens et al, 2011), a form of self-control that one might also infer is relevant to understanding cooking, where the longer one waits (to a point), the better the food becomes.…”