Gambling primates: reactions to a modified Iowa Gambling Task in humans, chimpanzees and capuchin monkeys

Abstract

Humans will, at times, act against their own economic self-interest, for example, in gambling situations. To explore the evolutionary roots of this behavior, we modified a traditional human gambling task, the Iowa Gambling Task (IGT), for use with chimpanzees, capuchin monkeys and humans. We expanded the traditional task to include two additional payoff structures to fully elucidate the ways in which these primate species respond to differing reward distributions versus overall quantities of rewards, a component often missing in the existing literature. We found that while all three species respond as typical humans do in the standard IGT payoff structure, species and individual differences emerge in our new payoff structures. Specifically, when variance avoidance and reward maximization conflicted, roughly equivalent numbers of apes maximized their rewards and avoided variance, indicating that the traditional payoff structure of the IGT is insufficient to disentangle these competing strategies. Capuchin monkeys showed little consistency in their choices. To determine whether this was a true species difference or an effect of task presentation, we replicated the experiment but increased the intertrial interval. In this case, several capuchin monkeys followed a reward maximization strategy, while chimpanzees retained the same strategy they had used previously. This suggests that individual differences in strategies for interacting with variance and reward maximization are present in apes, but not in capuchin monkeys. The primate gambling task presented here is a useful methodology for disentangling strategies of variance avoidance and reward maximization.

Variation in primate decision-making under uncertainty and the roots of human economic behaviour

“…In other cases, the payoff contingencies may be adjusted across trials to test how animals modulate their choices when expected values shift. In many studies, animals first gain experience with reward contingencies in a learning phase to then examine stabilized choice preferences in a test phase [50][51][52][53][54][55][56][57], whereas other studies focus on how animals learn about the value and variance of different outcomes [58,59]. This basic kind of paradigm has been used with multiple primate species, including chimpanzees (Pan troglodytes) [50,58,59], bonobos (Pan paniscus) [50], gorilla (Gorilla gorilla) [59], rhesus macaques (Macaca mulatta) [51][52][53][54][55], Japanese macaques (Macaca fuscata) [59], capuchin monkeys (Sapajus apella) [56,58] and several lemur species (Lemur catta, Eulemur mongoz, Varecia rubra) [57], in some cases with comparisons with humans [58,60].…”

Face Discriminations by Orangutans (Pongo spp.) Vary as a Function of Familiarity

“…4). To do this, a cumulative performance index was calculated by taking the number of correct choices minus the number of incorrect choices across trial blocks (the total number of trials divided into four blocks; Glicksohn et al 2007;Proctor et al 2014). In order to classify learning, the cumulative performance index had to result in a monotonic function (Fig.…”

Monkeys (Sapajus apella and Macaca tonkeana) and great apes (Gorilla gorilla, Pongo abelii, Pan paniscus, and Pan troglodytes) play for the highest bid.

“…Animal subjects are expected to learn about relative outcome frequencies from experience, but previous studies on risk do not give clear evidence of whether or how this occurs (Bateson & Kacelnik, 1997;Brito-e-Abreu & Kacelnik, 1999;De Petrillo et al, 2015;Hayden et al, 2008;Heilbronner & Hayden, 2013, Proctor et al, 2014. For example, Yamada et al (2013) showed that, although macaques exhibited a strategy in the early stages of testing that was interpreted as risk seeking, they shifted to neutral or slightly risk-averse attitudes after exposure to the tests.…”