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

How chimpanzees (Pan troglodytes) perform in a modified emotional Stroop task

The emotional Stroop task is an experimental paradigm developed to study the relationship between emotion and cognition. Human participants required to identify the color of words typically respond more slowly to negative than to neutral words (emotional Stroop effect). Here we investigated whether chimpanzees (Pan troglodytes) would show a comparable effect. Using a touch screen, eight chimpanzees were trained to choose between two simultaneously presented stimuli based on color (two identical images with differently colored frames). In Experiment 1, the images within the color frames were shapes that were either of the same color as the surrounding frame or of the alternative color. Subjects made fewer errors and responded faster when shapes were of the same color as the frame surrounding them than when they were not, evidencing that embedded images affected target selection. Experiment 2, a modified version of the emotional Stroop task, presented subjects with four different categories of novel images: three categories of pictures of humans (veterinarian, caretaker, and stranger), and control stimuli showing a white square. Because visits by the veterinarian that include anaesthetization can be stressful for subjects, we expected impaired performance in trials presenting images of the veterinarian. For the first session, we found correct responses to be indeed slower in trials of this category. This effect was more pronounced for subjects whose last anaesthetization experience was more recent, indicating that emotional valence caused the slowdown. We propose our modified emotional Stroop task as a simple method to explore which emotional stimuli affect cognitive performance in nonhuman primates.PostprintPeer reviewe

The role of past interactions in great apes’ communication about absent entities

M. Bohn was supported by a scholarship of the German National Academic Foundation. J. Call was supported by the “SOMICS” ERC-Synergy grant (nr. 609819).Recent evidence suggests that great apes can use the former location of an entity to communicate about it. In this study we built on these findings to investigate the social cognitive foundations of great apes’ communicative abilities. We tested whether great apes (n = 35) would adjust their requests for absent entities to previous interactions they had with their interlocutor. We manipulated the apes’ experience with respect to the interlocutor’s knowledge about the previous content of the now empty location, as well as their experience with the interlocutor’s competence to provide additional food items. We found that apes adjusted their requests to both of these aspects but failed to integrate them with one another. These results demonstrate a surprising amount of flexibility in great apes’ communicative abilities while at the same time suggesting some important limitations in their social communicative skills.PostprintPeer reviewe

Remembering past exchanges : apes fail to use social cues

The authors thank the Danish National Research Foundation [DNRF89] for funding.Nonhuman primates can remember events from their distant past. Furthermore, they can distinguish between very similar events by the process of binding. So far, research into long-term memory and binding has focused on the binding of contextual information, such as spatial surroundings. As such, we aimed to investigate if apes can bind and retrieve other types of information, specifically, social information. We presented great apes with three different object types; they learnt to exchange (via reinforcement) one of the object types with one experimenter and another type with a second, different, experimenter. The remaining object type was not reinforced by either of the experimenters. After a delay of two or ten weeks, we assessed the apes’ memory of which object type was exchanged with which experimenter. Additionally, we introduced a new experimenter to see if the apes could infer by exclusion that the remaining object type should be exchanged with the new experimenter. The apes successfully remembered which object types were exchanged, but failed to distinguish which object type was exchanged with whom. This failure to bind an object type to a specific person may have resulted from the apes learning to use a rule based on recency, as opposed to learning a conditional rule involving social information. However, results from a second experiment suggested they fail to incorporate social information even when no other information could guide successful performance. Our findings are consistent with research showing long-term memory in primates, but suggest that social information may not be bound in memory as readily as spatial or contextual information.Publisher PDFPeer 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

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

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

Conservatism and “copy-if-better” in chimpanzees (Pan troglodytes)

This work was funded by the project SOMICS, ERC-Synergy grant # 609819 to Josep Call.Social learning is predicted to evolve in socially living animals provided the learning process is not random but biased by certain socio-ecological factors. One bias of particular interest for the emergence of (cumulative) culture is the tendency to forgo personal behaviour in favour of relatively better variants observed in others, also known as the "copy-if-better" strategy. We investigated whether chimpanzees employ copy-if-better in a simple token-exchange paradigm controlling for individual and random social learning. After being trained on one token-type, subjects were confronted with a conspecific demonstrator who either received the same food reward as the subject (control condition) or a higher value food reward than the subject (test condition) for exchanging another token-type. In general, the chimpanzees persisted in exchanging the token-type they were trained on individually, indicating a form of conservatism consistent with previous studies. However, the chimpanzees were more inclined to copy the demonstrator in the test compared to the control condition, indicating a tendency to employ a copy-if-better strategy. We discuss our findings in light of their relevance to the emergence of cumulative culture.Publisher PDFPeer reviewe