Research with apes

The Department of Developmental and Comparative Psychology investigates the cognitive processes of the four great ape species (chimpanzees, bonobos, orangutans, gorillas), and those of a few other primate and mammalian species as well.

Chimpanzee	Bonobo	Orangutan	Gorilla

Social Cognition

We proceed under the assumption that we need a more differentiated view of ape social cognition than is currently available, that is, a view that goes beyond the question of "Do they or don't they have a theory of mind?" We have thus investigated a variety of different phenomena concerning what apes understand about others.

• Using a novel methodology, we have discovered that chimpanzees understand important aspects of intentional action. In work in progress, we seem to be replicating this finding using other methods. This is the first solid experimental demonstration of a nonhuman understanding intentions, and it has led us to reformulate our overall theory to some degree.
• We have also found that apes can in some circumstances take the visual perspective of others. We are currently investigating whether apes know what others can and cannot hear - to investigate the flexibility of their social cognitive skills. We are also investigating apes abilities to follow the gaze of others in a variety of novel context as well (e.g., following gaze by only observing the back of the head, around barriers).
• We have just discovered that chimpanzees attempt to conceal their approach visually - the first solid experimental demonstration of nonhuman deception in the sense that chimpanzees attempt to actively control what the other can and cannot see. They also attempt to avoid making noise in a similar situation - which again attests to the flexibility of this skill. We are also developing a new nonverbal false belief task for use with apes and other nonverbal organisms.
• We are very interested in apes' ability to cooperate with one another. One recent finding is that chimpanzees are much more skillful in a competitive version of a task than in a cooperative version of the same task. We are also in the process of looking at chimpanzees' ability to engage in cooperative problem-solving, and also in their sense of "fairness" at how food is doled out by humans.
• We have now completed our observational studies of the communicative gestures of all 4 great apes species (along with some gibbon and monkey species as well). We will soon be putting together an edited volume in which we explore in detail the gestural communication of the great apes. We are also looking at apes' knowledge of communicative intentions.
• We are continuing to investigate apes' skills of social learning and imitation. We are in the process of administering a battery of tasks that tap into different aspects of the process.

Beyond that, we study various phenomena to exxamine what primates know about their physical environment, such as:

• comprehension of space
• foraging strategies
• quantities and other numerical skills
• problem solving behavior
• drawing consequences
• causal correlations
• tool use

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Physical Cognition

We have recently argued against the traditional assumption that associative learning is simpler than causal learning. For organisms who have the requisite cognitive skills, it is actually the opposite: a causal connection makes things meaningful and therefore simpler.

• We have completed a series of studies demonstrating that apes can make a variety of inferences about the physical world, based on their causal knowledge. For example, they know that shaking a cup with a monkey biscuit inside produces a rattling sound whereas shaking an empty cup produces no noise. Even if the experimenter only shakes the empty cup, thus producing no noise, subjects can still immediately locate the food in the other cup. This is evidence of conjunctive negation. We have obtained analogous results with two other paradigms: occlusion and gravity. In occlusion experiments subjects know that food placed under one of two trays affects the resting angle of the tray that holds the food under it. In gravity experiments, subjects know that food placed inside one of two cups will fall if the cup is turned upside-down. Taken together, these experiments indicate that subjects understand many of the relations between objects and their effects in the environment.
• We have investigated the spatial memory skills of the great apes in the relatively large-scale space in the outdoor area at the Köhler Primate Center. We have found that orangutans know which foods are habitually located at which places in their environment. So they know 'what is where'. Moreover, chimpanzees can remember specific food locations for at least 18 months. This represents the longest retention period reported in the literature, although they may remember for even longer periods. We have also conducted studies on spatial reasoning in small scale space. Thus, we have presented apes with a battery of tests conducted on a platform in which a food reward is placed under one of several cups and various spatial transformations on the position of the cups are carried out. All ape species can master displacements involving transpositions, rotations, and invisible displacements at a level comparable to or greater than that of three-year-old children.
• Several recent studies have demonstrated great ape skills in understanding quantities and the conservation of quantities. All apes have been tested on relatively numerousness, that is, the ability to discriminate pairs of quantities. So far all apes species have been able to make the distinction between five and six pieces of food reliably. This is the first study to produce data on gorilla and bonobo numerical skills. Our ongoing project in this area is investigating the limits of relatively numerousness in these same subjects by presenting larger quantities (e.g., 9 vs. 10). These data will help to test the validity of the various hypotheses that have been formulated to account for the numerical skills of animals. We have also investigated Piagetian liquid conservation in bonobos, orangutans, and chimpanzees. We found that apes in general rely to a greater extent on visual information as opposed to logical necessity, although the individual differences are important and some particular orangutans may have some appreciation of the constancy of liquid quantities.
• We are currently working on several studies to investigate great ape skills of planning. This is a skill at which humans seem to excel, but it has been little studied in apes. We have presented apes with situations in which they have to select appropriate tools to get a reward, or choose the location from which they want to get the reward (with one location being ineffective). Complementary to this, we have some new studies on apes' ability to inhibit certain prepotent responses - a key feature of problem solving. Thus, we have presented all great apes with various inhibition problems based on reaching or reverse contingency paradigms. Taken together the results of these projects indicate that orangutans are the most skillful apes whereas gorillas seem to be the least skillful ones. The fact that orangutans outperformed chimpanzees and bonobos has important implications for the evolution of executive control in humans because orangutans are less closely related to humans than are chimpanzees and bonobos.

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Other Projects

The department also has two other relatively large-scale animal cognition projects.

• We are creating a cognitive battery designed to assess species and individual differences in the most important cognitive skills of the various primate species. There are 4 scales for physical cognition and 4 scales for social cognition. This instrument may be used to compare skills within and across individuals and species, and also to investigate psychometrically the correlational structure of a species’ cognitive skills (e.g., seeing whether physical tasks and social tasks correlate only within themselves or also across these domains).
• Instigated partially by the desire to compare ape cognition to that of other mammals and partially by the desire to investigate the role of human culture in cognition in general, we are continuing our work with domestic dogs. In two published and one submitted study, we have discovered that dogs know when they are being watched, and that they can take the visual perspective of others. These skills are not displayed by wolves - suggesting that they did indeed evolve during the domestication process in a human culture. We are also looking at whether dogs understand intentions and socially learn from demonstrations. We have also done a few studies with domestic goats.

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Research

Research at the Wolfgang Köhler Center is strictly observational; there is no invasive research of any kind. Apes are observed as they interact with their environments or groupmates, and also as they attempt to solve problems that are presented to them. Some of the topics to be investigated are as follows (detailed descriptions may be found in the book Primate Cognition by Michael Tomasello & Josep Call, Oxford University Press, 1997):

• We have a 20-year interest in the gestural communication of apes and how these skills develop in youngsters. To study these behaviors, we observe and videotape the apes (from observation towers) as they interact with one another.
• We are interested in how apes quantify objects and substances. To study this skill, we present subjects with various quantities of food or drinks on a platform in different configurations and let them choose. They do this by touching or pointing at the container whose contents they want.
• We are interested in processes of imitation and social learning. To study these skills, we allow some apes to observe other apes or humans solving problems before they are presented with the problem themselves. A related behavior involves apes using the looking direction of groupmates to discover interesting sights in their environments.

Apes are never deprived of their regular food or water in problem-solving studies. Instead, they work for special foods that they normally receive only rarely.
The results from this research will contribute to our knowledge of the behavior and cognition of our nearest primate relatives. In addtion, it will also help us to devise better and more effective enrichment programs for captive apes, because a deeper understanding of a species' cognitive skills is necessary to design facilities and programs that conform better to their needs. The research will also contribute to the education of the public by making the them aware of both similarities and differences between humans and apes, and so enhance their respect for these truly wonderful animals.

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The Apes and their Housing

The gorillas, bonobos, and orangutans at the Center come from various European zoos affiliated to the EEP and remain under the EEP's jurisdiction. The main group of chimpanzees come from another European research center and are all captive born. The center has five sets of indoor and outdoor areas, one each for each of the four species. Each indoor area consists of an indoor enclosure, sleeping, observation, and resting rooms. The outdoor areas contain natural vegetation, climbing structures, trees, water streams, and various other natural features.

Tabelle 1. Square meters available for each of the ape groups at the Köhler Center (Pongoland).

* shared enclosure with orangutans

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WKPRC

The Wolfgang Koehler Primate Research Center (Pongoland) is a project of the Max Planck Institute for Evolutionary Anthropology. It is operated in collaboration with the Leipzig Zoo. Research focuses on the behavior and cognition of the four species of great ape: chimpanzees (Pan troglodytes), gorillas (Gorilla gorilla), Organgutans (Pongo pygmaeus), and bonobos (Pan paniscus).

→ Wolfgang Köhler Primate Research Center

Internships

The Department of Developmental and Comparative Psychology offers unpaid internships to undergraduate students throughout the year.
To apply, please email your CV and a cover letter describing your research interests (both in English) to Daniel Hanus and Claudio Tennie (zoocoordinatoreva.mpg.de /
Tel. +49 (341) 3550 – 610 / Fax +49 (341) 3550 – 640)
Students are expected to spend a minimum of eight weeks at our institute - please state exactly when you would be available. If there are alternatives to your preferred period of time, please make sure to mention them as well, since this will increase your chances of getting a placement if your first choice does not work out. And finally: the sooner you apply, the better

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