Age-dependent cognitive inflexibility in great apes

The ability to suppress and/or change behaviour on the basis of negative feedback, often conceptualized as cognitive flexibility, has rarely been investigated in nonhuman great apes across a broad age range. In this study, 25 chimpanzees, Pan troglodytes, eight bonobos, Pan paniscus, seven orang-utans, Pongo abelii, and three gorillas, Gorilla gorilla, whose ages ranged from 5 to 48 years, were presented with a transparent Plexiglas rectangular box horizontally attached to their cage mesh. A square container, 7.5 cm2, fixed inside the apparatus contained a food reward (i.e. a grape). While the container rested on its central position the grape was not accessible. To retrieve the grape the subjects needed to grasp the handle connected to the reward container and displace it sideways to reach one of the lateral access windows. Subjects were intensively trained to displace the handle to a specific side (right or left, depending on the group) and then the rewarded side was reversed during the test. Performance in this reversal task did not differ significantly between species. However, a U-shaped relation between age and perseverative responding (i.e. moves to the previously rewarded side) was observed, extending findings with humans to our closest living primate relatives. (C) 2015 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.PostprintPeer reviewe

Comparative psychometrics: establishing what differs is central to understanding what evolves

Cognitive abilities cannot be measured directly. What we can measure is individual variation in task performance. In this paper, we first make the case for why we should be interested in mapping individual differences in task performance on to particular cognitive abilities: we suggest that it is crucial for examining the causes and consequences of variation both within and between species. As a case study, we examine whether multiple measures of inhibitory control for non-human animals do indeed produce correlated task performance; however, no clear pattern emerges that would support the notion of a common cognitive ability underpinning individual differences in performance. We advocate a psychometric approach involving a three-step programme to make theoretical and empirical progress: first, we need tasks that reveal signature limits in performance. Second, we need to assess the reliability of individual differences in task performance. Third, multi-trait multi-method test batteries will be instrumental in validating cognitive abilities. Together, these steps will help us to establish what varies between individuals that could impact their fitness and ultimately shape the course of the evolution of animal minds. Finally, we propose executive functions, including working memory, inhibitory control and attentional shifting, as a sensible starting point for this endeavour

The ape lottery : chimpanzees fail to consider spatial information when drawing statistical inferences

Funding: this work was supported by a research grant of the German Science Foundation DFG (grant # RA 2155/3-1) to Hannes Rakoczy and Josep Call. We acknowledge additional support by the Leibniz Association through funding for the Leibniz ScienceCampus Primate Cognition.Humans and nonhuman great apes share a sense for intuitive statistics, making intuitive probability judgments based on proportional information. This ability is of tremendous importance, in particular for predicting the outcome of events using prior information and for inferring general regularities from limited numbers of observations. Already in infancy, humans functionally integrate intuitive statistics with other cognitive domains, rendering this type of reasoning a powerful tool to make rational decisions in a variety of contexts. Recent research suggests that chimpanzees are capable of one type of such cross-domain integration: The integration of statistical and social information. Here, we investigated whether apes can also integrate physical information into their statistical inferences. We tested 14 sanctuary-living chimpanzees in a new task setup consisting of two “gumball machine”-apparatuses that were filled with different combinations of preferred and non-preferred food items. In four test conditions, subjects decided which of two apparatuses they wanted to operate to receive a random sample, while we varied both the proportional composition of the food items as well as their spatial configuration above and below a barrier. To receive the more favorable sample, apes needed to integrate proportional and spatial information. Chimpanzees succeeded in conditions in which we provided them either with proportional information or spatial information, but they failed to correctly integrate both types of information when they were in conflict. Whether these limitations in chimpanzees' performance reflect true limits of cognitive competence or merely performance limitations due to accessory task demands is still an open question.Publisher PDFPeer reviewe

The psychology of primate cooperation and competition : a call for realigning research agendas

Cooperation and competition are two key components of social life. Current research agendas investigating the psychological underpinnings of competition and cooperation in non-human primates are misaligned. The majority of work on competition has been done in the context of theory of mind and deception, while work on cooperation has mostly focused on collaboration and helping. The current impression that theory of mind is not necessarily implicated in cooperative activities and that helping could not be an integral part of competition might therefore be rather misleading. Furthermore, theory of mind research has mainly focused on cognitive aspects like the type of stimuli controlling responses, the nature of representation and how those representations are acquired, while collaboration and helping have focused primarily on motivational aspects like prosociality, common goals and a sense of justice and other-regarding concerns. We present the current state of these two bodies of research paying special attention to how they have developed and diverged over the years. We propose potential directions to realign the research agendas to investigate the psychological underpinnings of cooperation and competition in primates and other animals.PostprintPeer reviewe

Thirty years of great ape gestures

Open access funding provided by Max Planck Society.We and our colleagues have been doing studies of great ape gestural communication for more than 30 years. Here we attempt to spell out what we have learned. Some aspects of the process have been reliably established by multiple researchers, for example, its intentional structure and its sensitivity to the attentional state of the recipient. Other aspects are more controversial. We argue here that it is a mistake to assimilate great ape gestures to the species-typical displays of other mammals by claiming that they are fixed action patterns, as there are many differences, including the use of attention-getters. It is also a mistake, we argue, to assimilate great ape gestures to human gestures by claiming that they are used referentially and declaratively in a human-like manner, as apes’ “pointing” gesture has many limitations and they do not gesture iconically. Great ape gestures constitute a unique form of primate communication with their own unique qualities.Publisher PDFPeer reviewe

Cross-species variation in gaze following and conspecific preference among great apes, human infants and adults

Although previous studies have shown that many species follow gaze, few have directly compared closely related species, and thus its cross-species variation remains largely unclear. In this study, we compared three great ape species (bonobos, Pan paniscus, chimpanzees, Pan troglodytes, orang-utans, Pongo abelii) and humans (12-month-olds and adults) in their gaze-following responses to the videos of conspecific and allospecific models. In the video, the model turned his head repeatedly to one of two identical objects. We used a noninvasive eye-tracking technique to measure participants' eye movements, and used both conspecific and allospecific models as stimuli to examine their potential preference in following conspecific rather than allospecific gaze. Experiment 1 presented to great apes the videos of conspecific and human models. We found that all species followed the conspecific gaze. Chimpanzees did not follow the human gaze, whereas bonobos did. Bonobos reacted overall more sensitively than chimpanzees to both conspecific and human gaze. Experiment 2 presented to human infants and adults the videos of human, chimpanzee and orang-utan models. Both infants and adults followed the human gaze. Unlike adults, infants did not follow the ape gaze. Experiment 3 presented to great apes the videos of allospecific ape models. Consistent with experiment 1, chimpanzees did not follow the allospecific ape gaze, whereas bonobos and orang-utans did. Importantly, preferential following of conspecific gaze by chimpanzees (experiment 1) and human infants (experiment 2) was mainly explained by their prolonged viewing of the conspecific face and thus seems to reflect their motivation to attend selectively to the conspecific models. Taken together, we conclude that gaze following is modulated by both subject species and model species in great apes and humans, presumably a reflection of the subjects' intrinsic sensitivity to gaze and also their selective interest in particular models. (C) 2014 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.PostprintPeer reviewe

Chimpanzees infer the location of a reward on the basis of the effect of its weight

SummaryThe extent to which animals in general, and non-human primates in particular, understand physical causality is currently unclear [1,2]. One way to assess an animal's causal understanding is to test its ability to analyze a causal chain backwards — to infer cause from an effect [3]. In the study reported here, chimpanzees saw a given outcome (effect) of an action and had to infer the preceding event (cause) in order to solve the problem. More specifically, subjects saw a banana being hidden inside one of two opaque cups mounted on opposite sides of a balanced beam, but they were kept ignorant about the banana's exact location. Subsequently, the subjects witnessed the balance beam tilting to one side after the experimenter released it from its equilibrium position (the Balance condition). The chimpanzees preferentially (and from trial one) selected the lower, compared to the upper, cup. Two control conditions demonstrated that the chimpanzee subjects lacked an intrinsic preference for the lower cup when there was no movement involved (the Wedge condition) or when the balance beam was tilted by the experimenter's action (the Non-causal balance condition). We conclude that the chimpanzee subjects of our experiments demonstrated evidence of causal inference based on an object's weight

Inferential communication : bridging the gap between intentional and ostensive communication in non-human primates

This work was supported by the European Union’s Seventh Framework Programme (FP7/2007–2013)/ERC Grant 609819 (SOMICS).Communication, when defined as an act intended to affect the psychological state of another individual, demands the use of inference. Either the signaler, the recipient, or both must make leaps of understanding which surpass the semantic information available and draw from pragmatic clues to fully imbue and interpret meaning. While research into human communication and the evolution of language has long been comfortable with mentalistic interpretations of communicative exchanges, including rich attributions of mental state, research into animal communication has balked at theoretical models which describe mentalized cognitive mechanisms. We submit a new theoretical perspective on animal communication: the model of inferential communication. For use when existing proximate models of animal communication are not sufficient to fully explain the complex, flexible, and intentional communication documented in certain species, specifically non-human primates, we present our model as a bridge between shallower, less cognitive descriptions of communicative behavior and the perhaps otherwise inaccessible mentalistic interpretations of communication found in theoretical considerations of human language. Inferential communication is a framework that builds on existing evidence of referentiality, intentionality, and social inference in primates. It allows that they might be capable of applying social inferences to a communicative setting, which could explain some of the cognitive processes that enable the complexity and flexibility of primate communication systems. While historical models of animal communication focus on the means-ends process of behavior and apparent cognitive outcomes, inferential communication invites consideration of the mentalistic processes that must underlie those outcomes. We propose a mentalized approach to questions, investigations, and interpretations of non-human primate communication. We include an overview of both ultimate and proximate models of animal communication, which contextualize the role and utility of our inferential communication model, and provide a detailed breakdown of the possible levels of cognitive complexity which could be investigated using this framework. Finally, we present some possible applications of inferential communication in the field of non-human primate communication and highlight the role it could play in advancing progress toward an increasingly precise understanding of the cognitive capabilities of our closest living relatives.Publisher PDFPeer reviewe

Capuchins (Sapajus apella) and their aversion to inequity

Funding: Authors would like to acknowledge the financial support we received from the European Research Council (Synergy grant 609819 SOMICS provided to Josep Call) and the Swiss National Science Foundation (P2BEP3 175269 provided to Manon K. Schweinfurth).Humans have a strong sense of fairness and are usually averse to unequal treatment for the same action. Ever since Brosnan and de Waal showed a similar effect in capuchin monkeys (Sapajus apella), numerous studies using different experimental methods have been conducted to investigate whether animals show inequity aversion like humans do. Capuchin monkeys have become one of the best-studied animals in this area. Our first aim in this chapter was to synthesise the findings in this literature. We found that there is mixed evidence for inequity aversion in capuchin monkeys. Our second aim was to understand this variation by focusing on the following factors: the type of task used, the feeding regime outside the experiment and the monkeys’ social environment. To obtain data on some of these factors, as they are not always reported in published studies, we contacted researchers in the main laboratories conducting this work. We found that responses to inequity systematically varied as a function of the task demands and the feeding regime, but not the social environment. Tasks, in particular pulling tasks, that required participants to expend effort to get the food were more likely to detect evidence of inequity aversion. Moreover, monkeys with access to food before or after testing, were more likely to show inequity aversion than those whose access to food was temporarily restricted. We note that our survey is an explorative approach to investigate the variation in reports on inequity aversion in capuchin monkeys. We hope this chapter raises awareness of the complexity of the concept and generates new testable hypotheses, which might advance our understanding of the theoretical foundations of inequity aversion.PostprintPeer reviewe