Lindsey A. Drayton

A decade of theory of mind research on cayo santiago: Insights into rhesus macaque social cognition

Over the past several decades, researchers have become increasingly interested in understanding how primates understand the behavior of others. One open question concerns whether nonhuman primates think about others’ behavior in psychological terms, that is, whether they have a theory of mind. Over the last ten years, experiments conducted on the free‐ranging rhesus monkeys (Macaca mulatta) living on Cayo Santiago have provided important insights into this question. In this review, we highlight what we think are some of the most exciting results of this body of work. Specifically we describe experiments suggesting that rhesus monkeys may understand some psychological states, such as what others see, hear, and know, but that they fail to demonstrate an understanding of others’ beliefs. Thus, while some aspects of theory of mind may be shared between humans and other primates, others capacities are likely to be uniquely human. We also discuss some of the broader debates surrounding comparative theory of mind research, as well as what we think may be productive lines for future research with the rhesus macaques of Cayo Santiago. Am. J. Primatol. 78:106–116, 2016.

Insights into Intraspecies Variation in Primate Prosocial Behavior: Capuchins (Cebus apella) Fail to Show Prosociality on a Touchscreen Task

Over the past decade, many researchers have used food donation tasks to test whether nonhuman primates show human-like patterns of prosocial behavior in experimental settings. Although these tasks are elegant in their simplicity, performance within and across species is difficult to explain under a unified theoretical framework. Here, we attempt to better understand variation in prosociality by examining the circumstances that promote and hinder the expression of prosocial preferences. To this end, we tested whether capuchin monkeys (Cebus apella)—a species that has previously demonstrated prosocial preferences—would behave prosocially using a novel touchscreen task. In contrast to previous studies, we found that capuchins as a group did not prosocially deliver food to a partner. Importantly however, data from control conditions revealed that subjects demonstrated limited understanding of the reward contingencies of the task. We also compared individuals’ performance in the current study with their performance in a previously published prosociality study. We conclude by discussing how continuing to explore intraspecies variation in performance on prosocial tasks may help inform debates regarding the existence of other-regarding preferences in nonhuman species.

Capuchins’ (Cebus apella) sensitivity to others’ goal-directed actions in a helping context

As humans, our ability to help others effectively is at least in part dependent upon our capacity to infer others’ goals in a variety of different contexts. Several species of nonhuman primate have demonstrated that they will also help others in some relatively simple situations, but it is not always clear whether this helping is based on an understanding of another agent’s goals. Although the results of a number of different studies support the hypothesis that chimpanzees represent others’ goals in various helping contexts and are sensitive to these goals when actually helping others, less work has addressed whether more distantly related species actively represent goals when helping. To explore the cognitive mechanisms underlying helping behaviors in species less closely related to humans, we tested whether a species of New World monkey—the brown capuchin (Cebus apella)—would provide an experimenter with a desired out-of-reach object more often than an alternative object when the experimenter attempted to obtain the former object only. We found that capuchins reliably helped by providing the experimenter’s goal object (Experiment 1) and that explanations based on the use of several less sophisticated strategies did not account for the overall pattern of data (Experiments 2–4). Results are thus consistent with the hypothesis that capuchins help others based on an understanding of their goals although more work is needed to address the possibility that capuchins may be responding to gestural and postural factors alone.

Endowment Effects in Gorillas (Gorilla gorilla)

Reports of endowment effects in nonhuman primates have received considerable attention in the comparative literature in recent years. However, little is known about the mechanisms underlying these effects. Continuing to explore endowment effects across different species of primate may reveal subtle differences in behavior that can help formulate specific hypotheses about the relevant mechanisms and the social and ecological factors that have shaped them. In this study, we use a paradigm that has previously been used to test chimpanzees (Pan troglodytes) and orangutans (Pongo spp.) to explore whether western lowland gorillas (Gorilla gorilla) exhibit comparable endowment effects. We find that gorillas exhibit endowment effects when in possession of food, but not nonfood, items, and that they show a statistically stronger effect than chimpanzees but not orangutans. These findings are consistent with the hypothesis that mechanisms for endowment effects in primates may be related to inhibitory control or risk aversion.

Psychopaths fail to automatically take the perspective of others

Significance Psychopathic individuals behave in callous and antisocial ways that suggest that these individuals fail to consider what others are thinking (i.e., theory of mind). However, most empirical studies of psychopathy find that, despite their behavior, psychopathic individuals have an intact theory of mind: they successfully predict other’s perspectives. Here, we show that psychopathic individuals have a previously unobserved cognitive deficit that might explain their pattern of destructive and antisocial behavior. We report that psychopathic individuals fail to automatically take the perspective of others, but can deliberately take the perspective of others. These findings suggest that psychopathic individuals have the ability to take the perspective of others but lack the propensity to do so. Psychopathic individuals display a chronic and flagrant disregard for the welfare of others through their callous and manipulative behavior. Historically, this behavior is thought to result from deficits in social-affective processing. However, we show that at least some psychopathic behaviors may be rooted in a cognitive deficit, specifically an inability to automatically take another person’s perspective. Unlike prior studies that rely solely on controlled theory of mind (ToM) tasks, we employ a task that taps into automatic ToM processing. Controlled ToM processes are engaged when an individual intentionally considers the perspective of another person, whereas automatic ToM processes are engaged when an individual unintentionally represents the perspective of another person. In a sample of incarcerated offenders, we find that psychopathic individuals are equally likely to show response interference under conditions of controlled ToM, but lack a common signature of automatic ToM known as altercentric interference. We also demonstrate that the magnitude of this dysfunction in altercentric interference is correlated with real-world callous behaviors (i.e., number of assault charges). These findings suggest that psychopathic individuals have a diminished propensity to automatically think from another’s perspective, which may be the cognitive root of their deficits in social functioning and moral behavior.