How Is Chimpanzee Self-Control Influenced by Social Setting?

Abstract

Self-control is often required in natural situations involving interactions with other individuals, and personal self-control can be compromised if other individuals act impulsively. In this study, we tested self-control in pairs of chimpanzees in a variety of settings where at least one chimpanzee of each pair performed an established test for self-control in which candies accumulated one at time as long as the chimpanzee did not eat any of them. When tested alone, some chimpanzees exhibited greater self-control as compared to when tested alongside a chimpanzee that independently performed the same type of test. However, when the nonfocal animal freely consumed rewards while the focal chimpanzee performed the accumulation task, the self-control of some focal chimpanzees was elevated as compared to when working alone. Finally, when the focal and nonfocal animals worked jointly on the same test and the number of rewards accumulated was dependent on both animals' continued ability to inhibit eating the items, chimpanzees performed the same when housed together or in adjacent enclosures. On the whole, the effects of social setting were modest, but these results may relate to the literature on vicarious depletion of self-control, and they present interesting avenues for future research.

Working and waiting for better rewards: Self-control in two monkey species (Cebus apella and Macaca mulatta)

“…It follows that the general outcome of this study – that these monkeys tolerated delays and work periods of several seconds in order to obtain a larger supply of food pellets – is reliable as well. Moreover, this general outcome is consistent with multiple previous studies involving these and related species illustrating that nonhuman primates are capable of self-control and delay of gratification within certain temporal and reward parameters (e.g., Addessi and Rossi, 2011; Beran, 2002; Dufour et al, 2007; Evans et al, 2012a, 2012b; Freeman et al, 2009; Stevens et al, 2005a, 2005b; Tobin et al, 1996). …”

Chimpanzees (Pan troglodytes) transfer tokens repeatedly with a partner to accumulate rewards in a self-control task

“…Specifically, chimpanzees can delay gratification for similar amounts of time as human children (Beran and Evans 2006), and like children, chimpanzees will divert their attention from task rewards resulting in greater delay of gratification (Evans and Beran 2007). Despite these results, we have an incomplete picture of self-control in chimpanzees as it manifests in a social setting (but see Boysen and Bernston 1995; Evans et al 2012), and as it might manifest in other colonies of captive animals.…”

“…Instead of the experimenter physically delivering the food rewards, a computer was set up so that rewards were delivered via an automated dispenser (see Beran and Evans 2006; Evans et al 2012). This apparatus consisted of two Med Associates dispensers controlled by a Dell Optiplex personal computer via a Keithley Instruments digital I/O board.…”

“…The accumulation procedure was automatically terminated if all candies were accumulated, effectively ending the trial and preventing any extra token passes. All chimpanzees had experience using the automated food dispenser in previous accumulation tasks (e.g., Beran and Evans 2006; Evans et al 2012). We ran one pretest trial for each chimpanzee with 20 pieces of food before testing to ensure they would engage this new experimental setup.…”

“…In a recent paper, we demonstrated that chimpanzees were mostly successful in delay of gratification tasks across a range of relatively passive social situations (Evans et al 2012). When chimpanzees worked independently on accumulation tasks in adjacent enclosures, some chimpanzees demonstrated impairments in performance compared to when they were tested alone, though there was not a direct relationship between the time at which each chimpanzee ended its own trial and when the partner ended its trial.…”