Anderson, J.R. and Gallup, G.G. (1997) Self-recognition in Saguinus? A critical essay. Animal Behaviour, 54, 1563-1567.

Recently, Hauser et al. (1995) claimed to have shown evidence of mirror self-recognition in some individuals of a small New World monkey species, Saguinus oedipus, the cotton- top tamarin. This claim requires careful scrutiny. If the reported results are valid and reliable, they will imply methodological inadequacies in most if not all previous studies that have tried to find mirror self-recognition in monkeys. Furthermore, they would also fatally challenge the widely accepted view that members of the great ape species and humans are the only primates with a sufficiently integrated awareness of self to allow mirror-mediated self-recognition (Gallup 1982, 1991; Povinelli 1993). Here, we argue that the evidence presented by Hauser et al. (1995) to suggest that cotton-top tamarins recognize themselves in a mirror is so inadequate as to be invalid. In so doing, we point out several basic conceptual and methodological considerations that need to be addressed in any attempt to find mirror self-recognition in monkeys.

Bermejo, M. and Illera, G. (1999) Tool-set for termite-fishing and honey extraction by wild chimpanzees in the Lossi Forest, Congo. Primates, 40, 619-627.

The use of perforating sticks and flexible stalks in combination for termite fishing and a complex tool-set of three components used sequentially (stout chisel, bodkin, and dip- stick) to penetrate melipone and ground-dwelling bee hives by Pan troglocytes troglodytes are documented or inferred from circumstantial evidence. Functionally, termite extraction tools were similar to other locations in west and central Africa. but the plants and the number of raw material species used were different. Tools varied in the degree of modification (fraying ends). Chimpanzees in the Lossi forest seem to be able to use the tools not in a stereotyped fashion, but in a flexible, insightful way. The extraction of Melipone honey using large pieces of wood as pounding tools has rarely been recorded elsewhere. The most impressive technological solution to the honey-getting problem by wild chimpanzees was shown by this study. This is the only known use of a tool-set of three components in sequence to extract honey by wild chimpanzees.

Biro, D. and Matsuzawa, T. (1999) Numerical ordering in a chimpanzee (Pan troglodytes): Planning, executing, and monitoring. Journal of Comparative Psychology, 113, 178-185.

Perceptual and cognitive processes underlying the skill of ordering numerals were assessed in a female chimpanzee (Pan troglodytes) with previous experience in computer-assisted numerical competence tasks. The subject was required to order 3 numerals from the range of 0-9 into an ascending series, with occasional probe trials (referred to as switch trials) in which the positions of the 2nd and 3rd numerals were exchanged immediately after the selection of the 1st. On these trials, errors were scored frequently, whereas correct responses to the intermediate numeral became reliably slower. These and other data indicated that the subject had already established, before making the 1st choice, (a) the correct sequence in which she was to select the numerals and (b) the motor sequence leading to a,correct answer. These findings show that a 3-unit ordering task is supported in the chimpanzee, much as it is in humans, by planning, executing, and monitoring phases.

Boesch, C. and Tomasello, M. (1998) Chimpanzee and human cultures. Current Anthropology, 39, 591-614.

Culture has traditionally been attributed only to human beings. Despite growing evidence of behavioral diversity in wild chimpanzee populations, most anthropologists and psychologists still deny culture to this animal species. We argue here that culture is not monolithic but a set of processes. These processes show much diversity both in the social norms and models that determine which individuals will be exposed to particular cultural variants and what cultural variants will be present in the population and in the social learning mechanisms that determine the fidelity of transmission of the variants over time. Recognition of the diversity of these processes is important because it affects cultural dissemination, cultural evolution, and the complexity of cultural artifacts. A comparison of chimpanzee and human cultures shows many deep similarities, thus suggesting that they share evolutionary roots. Two possible differences between the two species are discussed. First, thanks to indirect means of transmission such as language, cultural dissemination is possible over greater stretches of time and space in humans than in chimpanzees. Second, human cultures rely more intensively than chimpanzee cultures on cumulative cultural evolution through the ratchet effect, which allows the accumulation of modifications over time and produces more elaborate cultural artifacts.

Boysen, S.T. and Himes, G.T. (1999) Current issues and emerging theories in animal cognition. Annual Review of Psychology, 50, 683-705.

Comparative cognition is an emerging interdisciplinary field with contributions from comparative psychology, cognitive/experimental and developmental psychology, animal learning, and ethology, and is poised to move toward greater understanding of animal and human information-processing, reasoning, memory, and the phylogenetic emergence of mind. This chapter highlights some current issues and discusses four areas within comparative cognition that are yielding new approaches and hypotheses for studying basic conceptual capacities in nonhuman species. These include studies of imitation, tool use, mirror self- recognition, and the potential for attribution of mental states by nonhuman animals. Though a very old question in psychology, the study of imitation continues to provide new avenues for examining the complex relationships among and between the levels of imitative behaviors exhibited by many species. Similarly, recent work in animal tool use, mirror self-recognition (with all its contentious issues), and recent attempts to empirically study the potential for attributional capacities in nonhumans, all continue to provide fresh insights and novel paradigms for addressing the defining characteristics of these complex phenomena.

Boysen, ST, Berntson, GG, Shreyer, TA, Hannan, MB (1995) Indicating acts during counting by a chimpanzee (Pan-troglodytes) . Journal of Comparative Psychology, Vol.109, No.1, Pp.47-51 .

A chimpanzee (Pan troglodytes) experienced in counting arrays of 0-7 items and trained for comprehension of number symbols, spontaneously displayed a variety of indicating acts (e.g., Pointing, touching, and rearranging items) during counting. Twenty-five sessions were videotaped, and an trials were evaluated for the relations among number of items presented, number of indicating acts displayed, and the arabic number selected to represent the array. Significant correlations included the relations between number of items and the cardinal number selected by the animal, between the number of items and indicating acts displayed by the chimpanzee, and between the number of indicating acts and the numeral selected. These data suggest that the use of indicating acts by this animal may have functional significance and serves as an organizing schema, comparable to similar behaviors observed in children in the early stages of learning to count.

Brannon, E.M. and Terrace, H.S. (1998) Ordering of the numerosities 1 to 9 by monkeys. Science, 282, 746-749.

A fundamental question in cognitive science is whether animals can represent numerosity (a property of a stimulus that is defined by the number of discriminable elements it contains) and use numerical representations computationally. Here, it was shown that rhesus monkeys represent the numerosity of visual stimuli and detect their ordinal disparity. Two monkeys were first trained to respond to exemplars of the numerosities 1 to 4 in an ascending numerical order (1 --> 2 --> 3 --> 4). As a control for non-numerical cues, exemplars were varied with respect to size, shape, and color, The monkeys were later tested, without reward, on their ability to order stimulus pairs composed of the novel numerosities 5 to 9. Both monkeys responded in an ascending order to the novel numerosities, These results show that rhesus monkeys represent the numerosities 1 to 9 on an ordinal scale.

Brannon, E.M. and Terrace, H.S. (2000) Representation of the numerosities 1- 9 by rhesus macaques (Macaca mulatta). Journal of Experimental Psychology- Animal Behavior Processes, 26, 31-49.

Three rhesus monkeys (Macaca mulatta) were trained to respond to exemplars of I, 2, 3, and 4 in an ascending, descending, or a nonmonotonic numerical order (1-->2-->3-->4, 4-->3-->2-->1, 3- ->1-->4-->2). The monkeys were then tested on their ability to order pairs of the novel numerosities 5-9. In Experiment I, all 3 monkeys ordered novel exemplars of the numerosities 1- 4 in ascending or descending order. The attempt to train a nonmonotonic order (3-->1-->4-->2) failed. In Experiment 2A, the 2 monkeys who learned the ascending numerical rule ordered pairs of the novel numerosities 5-9 on unreinforced trials. The monkey who learned the descending numerical rule failed to extrapolate the descending rule to new numerosities. In Experiment 2B all 3 monkeys ordered novel exemplars of pairs of the numerosities 5-9. Accuracy and latency of responding revealed distance and magnitude effects analogous to previous findings with human participants (R. S. Moyer & T. K. Landaeur, 1967). Collectively these studies show that monkeys represent the numerosities 1-9 on at least an ordinal scale.

Byrne, RW, Russon, AE (1998) Learning by imitation: a hierarchical approach. Behavioral and Brain Sciences, Vol.21, No.5, P.667-721 (23 Pages).

To explain social learning without invoking the cognitively complex concept of imitation, many learning mechanisms have been proposed. Borrowing an idea used routinely in cognitive psychology, we argue that most of these alternatives can be subsumed under a single process, priming, in which input increases the activation of stored internal representations. Imitation itself has generally been seen as a ''speciaI faculty'' This has diverted much research towards the all-ornone question of whether an animal can imitate, with disappointingly inconclusive results. In the great apes, however, voluntary learned behaviour is organized hierarchically. This means that imitation can occur at various levers, of which we single out two clearly distinct ones: the ''action level,'' a rather detailed and linear specification of sequential acts, and the ''program level,'' a broader description of subroutine structure and the hierarchical layout of a behavioural ''program.'' Program level imitation is a high-level, constructive mechanism, adapted for the efficient learning of complex skills and thus not evident in the simple manipulations used to test for imitation in the laboratory. As examples, we describe the food preparation techniques of wild mountain gorillas and the imitative behaviour of orangutans undergoing ''rehabilitation'' to the wild. Representing and manipulating relations between objects seems to be one basic building block in their hierarchical programs. There is evidence that great apes suffer from a stricter capacity limit than humans in the hierarchical depth of planning. We reinterpret some chimpanzee behaviour previously described as ''emulation'' and suggest that all great apes may be able to imitate at the program level. Action level imitation is seldom observed in great ape skill learning, and may have a largely social role, even in humans.

Call, J, Tomasello, M (1994) Production and comprehension of referential pointing by orangutans (Pongo-pygmaeus). Journal of Comparative Psychology, Vol.108, No.4, Pp.307-317.

We report 3 studies of the referential pointing of 2 orangutans (Pongo pygmaeus). Chantek was raised in an enculturated environment; Puti, raised in a nursery, had a more typical captive life. In Experiment 1, flexibility of pointing behavior was investigated by requiring subjects to point in novel circumstances (for an out-of- sight tool, not food). In Experiment 2, we investigated the orangutans' comprehension of the significance of a human point in helping them to locate food. In Experiment 3, we investigated whether these pointing subjects comprehended that a human recipient must be looking for the point to achieve its attention directing goal. In all experiments the enculturated orangutan showed better understanding of pointing than the captive orangutan. This finding is consistent with recent studies that have found differences in the cognitive and social-cognitive abilities of apes that have had different types of experience with humans.

Cheney, D. and Seyfarth, R. (1992) How monkeys see the world. Behavioral and Brain Sciences, 15, 135-&.

Our book examines the mechanisms that underlie social behavior and communication in East African vervet monkeys. Our goal is to describe the sophistication of primate intelligence and to probe its limits. We suggest that vervets and other primates make good primatologists. They observe social interactions, recognize the relations that exist among others, and classify relationships into types. Monkeys also use sounds to represent features of their environment and compare different vocalizations according to their meaning. However, while monkeys may use abstract concepts and have motives, beliefs, and desires, their mental states are apparently not accessible: they do not know what they know. In addition, monkeys seem unable to attribute mental states to others: they lack a "theory of mind." Their inability to examine their own mental states or to attribute mental states to others severely constrains their ability to transmit information or to deceive one another. It also limits the extent to which their vocalizations can be called semantic. Finally, the skills that monkeys exhibilt in social behavior are apparently domain specific. For reasons that are presently unclear, vervets exhibit adaptive specializations in social interactions that are not extended to their interactions with other species (although they should be).


[not in handout, see intranet]

Custance, D, Whiten, A, Fredman, T (1999) Social learning of an artificial fruit task in capuchin monkeys (cebus apella). Journal of Comparative Psychology, Vol.113, No.1, Pp.1323.

Social learning in 11 human-raised capuchin monkeys (Cebus apella) was investigated using an artificial fruit that was designed as an analogue of natural foraging problems faced by primates. Each subject observed a human model open each of 3 principal components on the fruit in 1 of 2 alternative ways (''morphs''). The capuchin monkeys reproduced, to differing extents, the alternative techniques used for opening 1 component of the task (poking vs; pulling while twisting out a pair of smooth plastic bolts) but not the other 2. From the subjects' actions on the bolt latch, independent coders could recognize which morph they had witnessed, and they observed a degree of matching to the demonstrator's act consistent with simple imitation or object movement reenactment (A learns from watching B how an object, or parts of an object, move). Thus, these capuchins were capable of more complex social learning than has been recently ascribed to monkeys.

Custance, DM, Whiten, A, Bard, KA (1995) Can young chimpanzees (Pan- troglodytes) imitate arbitrary actions -Hayes and Hayes (1952) revisited. Behaviour, Vol.132, No.Pt11-12, Pp.837-859.

Contrary to recent scepticism, systematic use of an experimental approach suggested by HAYEs & HAYEs (1952) shows that chimpanzees can imitate novel actions. Two chimpanzees imitated 13 and 17 novel arbitrary gestures, respectively. They were first taught to reproduce 15 gestures on the command, ''Do this!'', and then presented with 48 novel items. Using a rigourous coding system, two independent observers correctly identified a significant number of the chimpanzees' imitations (p < 0.0001). We conclude that after a period of tuition chimpanzees can go on to imitate arbitrary actions,

de Waal, FBM (1997) The chimpanzee’s service economy: food for grooming. Evolution and Human Behavior, Vol.18, No.6, Pp.375-386.

Evidence is presented that the reciprocal exchange of social services among chimpanzees (Pan troglodytes) rests on cognitive abilities that allow current behavior to be contingent upon a history of interaction. Food sharing within a captive colony of chimpanzees was studied by means of 200 food trials, conducted on separate days over a 3-year period, in which 6,972 approaches occurred among the nine adults in the colony. The success rate of each adult, A, to obtain food from another adult, B, was compared with grooming interactions between A and B in the 2 hours prior to each food trial. The tendency of B to share with A was higher if A had groomed B than if A had not done so. The exchange was partner-specific, i.e., the effect of previous grooming on the behavior of food possessors was limited to the grooming partner. Grooming did not affect subsequent sharing by the groomer, only by the groomee. The effect of grooming was greatest for pairs of adults who rarely groomed. Nevertheless, the effect was general: 31 dyadic directions showed an increase in sharing following grooming, and only 11 a decrease. Food possessors actively resisted approaches by individuals who had not groomed them. After food trials there was a significant reduction of grooming by previous possessors towards those individuals with whom they had shared. (C) 1997 Elsevier Science Inc.

de Waal, F.B.M. and Berger, M. (2000) Payment for labour in monkeys. Nature, 404, 583. (

Cooperative hunting, in which several individuals pursue prey but only one makes a capture, is central to theories of human social and moral evolution . But among other primates, it is known only from the chimpanzee and a large-brained neotropical monkey, the capuchin . It probably evolved through either mutualism, in which two or more cooperators benefit simultaneously, or reciprocal altruism, in which one favour is repaid by another 9 . We have found that brown capuchins (Cebus apella) share rewards obtained by a joint effort more readily than rewards obtained individually. Even if hunting in the field involves selfish opportunism, this food incentive will greatly enhance the persistence of cooperation.

Deblois, ST, Novak, MA (1994) Object permanence in rhesus-monkeys (Macaca-mulatta). Journal of Comparative Psychology, Vol.108, No.4, Pp.318-327.

We evaluated the performance of 6 adult rhesus monkeys (Macaca mulatra) on object permanence tasks. In Experiment 1, monkeys received search tasks that correspond to Stages 4, 5, and 6 of object permanence. Subjects were successful on tasks of visible displacements (Stages 4 and 5) but failed to find the object in invisible displacements (Stage 6). The monkeys adopted a search strategy of investigating a specific hiding location. In Experiment 2, monkeys were given a second opportunity to find the object if they investigated a location that was part of the displacement on their first search. Subjects relied on the same search strategy identified in Experiment 1. In Experiment 3, the experimenter hid the object in her hand rather than a container. The monkeys failed to recover the object, and individual differences were found in the strategies used. These results suggest that the upper limit of object permanence in rhesus monkeys is stage 5.

Deblois, ST, Novak, MA, Bond, M (1999) Can memory requirements account for species' differences in invisible displacement tasks?. Journal of Experimental Psychology-Animal Behavior Processes, Vol.25, No.2, Pp.168-176.

We tested the hypothesis that poor performance on the Piagetian invisible displacement task is related to increased memory requirements. Rhesus monkeys and orangutans received 3 types of problems (invisible, visible, and no transfer problems) each containing a number of steps equivalent to that of standard invisible displacements. if failure to solve invisible displacements was due to increased memory requirements, then the primates should perform at chance level on all 3 problems. However, rhesus monkeys solved visible and no transfer problems, but not invisible transfer problems. Half of the orangutans solved all 3 transfer problems, although their performance on invisible transfer problems was lower than that on the other problems. A subsequent cuing phase led to improved performance, and a few monkeys solved invisible transfer problems.

Dehaene, S., Dehaene-Lambertz, G. and Cohen, L. (1998) Abstract representations of numbers in the animal and human brain. Trends in Neurosciences, 21, 355-361.

There is evidence to suggest that animals, young infants and adult humans possess a biologically determined. domain-specific representation of number and of elementary arithmetic operations. Behavioral studies in infants and animals reveal number perception, discrimination and elementary calculation abilities in non-verbal organisms. Lesion and brain-imaging studies in humans indicate that a specific neural substrate, located in the left and right intraparietal area, is associated with knowledge of numbers and their relations ('number sense'). The number domain is a prime example where strong evidence points to an evolutionary endowment of abstract domain-specific knowledge in the brain because there are parallels between number processing in animals and humans.The numerical distance effect, which refers to the finding that the ability to discriminate between two numbers improves as the numerical distance between them increases, has been demonstrated in humans and animals, as has the number size effect,which refers to the finding that for equal numerical distance, discrimination of two numbers worsens as their numerical size increases.

Depy, D, Fagot, J, Vauclair, J (1998) Comparative assessment of distance processing and hemispheric specialization in humans and baboons (papio papio) download full text of article. Brain and Cognition, Vol.38, No.2, Pp.165-182.

This comparative study explored the ability to process distance and its lateralization in humans and baboons. Using a conditional matching-to-sample procedure in a divided-held format, subjects had to decide whether or not the distance between a line and a dot belonged to a short- or a longdistance category. Experiments 1, 2, and 4 demonstrated the ability of baboons to process and categorize distances. Moreover, humans showed better distance processing for right visual field/left hemisphere presentations than for left visual field/right hemisphere (LVF-RH) displays (Experiments 1-2). The same bias was found in baboons (Experiment 1), but in a weaker way. In Experiment 3, naive human individuals were tested and the difficulty of the discrimination was enhanced. There was a LVF-RH advantage which vanished with practice. Results are discussed by referring to theories (i.e., Kosslyn, 1987) of visuospatial processing for coordinate and categorical judgments. (C) 1998 Academic Press.

Desimone, R (1998) Visual attention mediated by biased competition in extrastriate visual cortex. Philosophical Transactions of the Royal Society of London Series B-Biological Sciences, Vol.353, No.1373, Pp.12451255.

According to conventional neurobiological accounts of visual attention, attention serves to enhance extrastriate neuronal responses to a stimulus at one spatial location in the visual field. However, recent results from recordings in extrastriate cortex of monkeys suggest that any enhancing effect of attention is best understood in the context of competitive interactions among neurons representing all of the stimuli present in the visual field. These interactions can be biased in favour of behaviourally relevant stimuli as a result of many different processes, both spatial and non-spatial, and both bottom-up and top-down. The resolution of this competition results in the suppression of the neuronal representations of behaviourally irrelevant stimuli in extrastriate cortex. A main source of top-down influence may derive from neuronal systems underlying working memory.

Eddy, TJ, Gallup, GG, Povinelli, DJ (1996) Age-differences in the ability of chimpanzees to distinguish mirror- images of self from video images of others. Journal of Comparative Psychology, Vol.110, No.1, Pp.38-44.

To evaluate Heyes's (1994) claim that chimpanzees are incapable of using mirrored information to obtain otherwise unavailable information about the self, we exposed two different age groups of chimpanzees (3-year-olds and 7- to 10-year-olds) to mirrors and video images of conspecifics. Their reactions to these stimuli were videotaped and were later scored for behavioral indices of self- recognition by a trained observer who was blind to the purpose and conditions of the study. Some types of behavior (contingent facial and body movements) were clearly influenced by the type of stimulus that the chimpanzees were viewing but not by age; however, other behaviors (self-exploration) were affected by age in conjunction with the type of stimulus the animals were viewing. The results suggest that, unlike self-exploratory behavior, contingent facial and body movements may not, by themselves, be reliable indicators of self- recognition.

Gallistel, C.R. and Gelman, R. (2000) Non-verbal numerical cognition: from reals to integers. Trends in Cognitive Sciences, 4, 59-65.

Data on numerical processing by verbal (human) and non-verbal (animal and human) subjects are integrated by the hypothesis that a non-verbal counting process represents discrete (countable) quantities by means of magnitudes with scalar variability. These appear to be identical to the magnitudes that represent continuous (uncountable) quantities such as duration. The magnitudes representing countable quantity are generated by a discrete incrementing process, which defines next magnitudes and yields a discrete ordering. In the case of continuous quantities, the continuous accumulation process does not define next magnitudes, so the ordering is also continuous ('dense'). The magnitudes representing both countable and uncountable quantity are arithmetically combined in, for example, the computation of the income to be expected from a foraging patch. Thus, on the hypothesis presented here, the primitive machinery for arithmetic processing works with real numbers (magnitudes).

Gallistel, C.R. and Gelman, R. (1992) Preverbal and Verbal Counting and Computation. Cognition, 44, 43-74.

We describe the preverbal system of counting and arithmetic reasoning revealed by experiments on numerical representations in animals. In this system, numerosities are represented by magnitudes, which are rapidly but inaccurately generated by the Meck and Church (1983) preverbal counting mechanism. We suggest the following. (1) The preverbal counting mechanism is the source of the implicit principles that guide the acquisition of verbal counting. (2) The preverbal system of arithmetic computation provides the framework for the assimilation of the verbal system. (3) Learning to count involves, in part, learning a mapping from the preverbal numerical magnitudes to the verbal and written number symbols and the inverse mappings from these symbols to the preverbal magnitudes. (4) Subitizing is the use of the preverbal counting process and the mapping from the resulting magnitudes to number words in order to generate rapidly the number words for small numerosities. (5) The retrieval of the number facts, which plays a central role in verbal computation, is mediated via the inverse mappings from verbal and written numbers to the preverbal magnitudes and the use of these magnitudes to find the appropriate cells in tabular arrangements of the answers. (6) This model of the fact retrieval process accounts for the salient features of the reaction time differences and error patterns revealed by experiments on mental arithmetic. (7) The application of verbal and written computational algorithms goes on in parallel with, and is to some extent guided by, preverbal computations, both in the child and in the adult.

Gallup, GG, Povinelli, DJ, Suarez, SD, Anderson, JR, Lethmate, J, Menzel, EW (1995) Further reflections on self-recognition in primates. Animal Behaviour, Vol.50, No.Pt6, Pp.1525-1532 .

A review of the literature, together with a reanalysis of existing data and some additional data, was used to show that Heyes' (1994, Anim. Behav., 47, 909-919) recent critique of self- recognition research in primates is without merit. Heyes' contention, that self- recognition is an artefact of incomplete recovery from anaesthetization and species differences in ambient face touching, is contrary to (1) the temporal parameters of the mark test, (2) responses that chimpanzees, Pan troglodytes, make to control body marks (i.e. those that can be seen without a mirror), (3) results from studies that have not used anaesthesia, (4) responses that chimpanzees make to unmarked portions of the face, (5) the absence of a correlation between developmental changes in face touching and self-recognition, (6) differences among chimpanzees in patterns of mirror self-directed behaviour and normal self-grooming and (7) the absence of substantial species differences in face-touching behaviour. (C) 1995 The Association for the Study of Animal Behaviour

Ghazanfar, A.A. and Hauser, M.D. (1999) The neuroethology of primate vocal communication: substrates for the evolution of speech. Trends in Cognitive Sciences, 3, 377-384.

In this article, we review behavioral and neurobiological studies of the perception and use of species-specific vocalizations by non-human primates. At the behavioral level, primate vocal perception shares many features with speech perception by humans. These features include a left-hemisphere bias towards conspecific vocalizations, the use of temporal features for identifying different calls, and the use of calls to refer to objects and events in the environment. The putative neural bases for some of these behaviors have been revealed by recent studies of the primate auditory and prefrontal cortices. These studies also suggest homologies with the human language circuitry. Thus, a synthesis of cognitive, ethological and neurobiological approaches to primate vocal behavior is likely to yield the richest understanding of the neural bases of speech perception, and might also shed light on the evolutionary precursors to language.

Hauser, M.D., MacNeilage, P. and Ware, M. (1996) Numerical representations in primates. Proceedings of the National Academy of Sciences of the United States of America, 93, 1514-1517.

Research has demonstrated that human infants and nonhuman primates have a rudimentary numerical system that enables them to count objects or events, More recently, however, studies using a preferential looking paradigm have suggested that preverbal human infants are capable of simple arithmetical operations, such as adding and subtracting a small number of visually presented objects, These findings implicate a relatively sophisticated representational system in the absence of language. To explore the evolutionary origins of this capacity, we present data from an experiment with wild rhesus monkeys (Macaca mulatta) that methodologically mirrors those conducted on human infants, Results suggest that rhesus monkeys detect additive and subtractive changes in the number of objects present in their visual field, Given the methodological and empirical similarities, it ap pears that nonhuman primates such as rhesus monkeys may also have access to arithmetical representations, although alternative explanations must be considered for both primate species.

Heyes, C.M. (1998) Theory of mind in nonhuman primates. Behavioral and Brain Sciences, 21, 101-+.

Since the BBS article in which Premack and Woodruff (1978) asked "does the chimpanzee have a theory of mind?", it has been repeatedly claimed that there is observational and experimental evidence that apes have mental state concepts, such as "want" and "know." Unlike research on the development of theory of mind in childhood, however, no substantial progress has been made through this work with nonhuman primates. A survey of empirical studies of imitation, self-recognition, social relationships, deception, role-taking, and perspective-taking suggests that in every case where nonhuman primate behavior has been interpreted as a sign of theory of mind, it could instead have occurred by chance or as a product of nonmentalistic processes such as associative learning or inferences based on nonmental categories. Arguments to the effect that, in spite of this, the theory of mind hypothesis should be accepted because it is more parsimonious than alternatives or because it is supported by convergent evidence are not compelling. Such arguments are based on unsupportable assumptions about the role of parsimony in science and either ignore the requirement that convergent evidence proceed form independent assumptions, or fail to show that it supports the theory of mind hypothesis over nonmentalist alternatives. progress in research on theory of mind requires experimental procedures that can distinguish the theory of mind hypothesis from nonmentalist alternatives. A procedure that may have this potential is proposed. it uses conditional discrimination training and transfer tests to determine whether chimpanzees have the concept "see." Commentators are invited to identify flaws int he procedure and to suggest alternatives.

Inoue-Nakamura, N. and Matsuzawa, T. (1997) Development of stone tool use by wild chimpanzees (Pan troglodytes). Journal of Comparative Psychology, 111, 159-173.

At the age of 3.5 years, wild chimpanzees at Bossou, Guinea, begin to use hammer and anvil stones to crack oil-palm nuts to get the kernels. To clarify the developmental processes, the authors did a field experiment in which stones and oil-palm nuts were provided. Infant chimpanzees' stone-nut manipulation was observed and video recorded. Data were collected from 3 infants younger than 4 years old from 1992 to 1995. The authors analyzed 692 episodes of infants' stone-nut manipulation and 150 episodes of infants' observation of nut cracking performed by adults. Infants observed other chimpanzees' nut cracking and got the kernels from them. The stone-nut manipulation developed from a single action on a single object to multiple actions on multiple objects. Although infant chimpanzees at the age of 2.5 years already acquired basic actions necessary for nut cracking, they did not combine the actions in an appropriate sequence to perform actual nut cracking.

Itakura, S, Tanaka, M (1998) Use of experimenter-given cues during object- choice tasks by chimpanzees (Pan troglodytes), an orangutan (pongo pygmaeus), and human infants (homo sapiens). Journal of Comparative Psychology, Vol.112, No.2, Pp.119126.

In a series of experiments, chimpanzees (Pan troglodytes), an orangutan (Pongo pygmaeus), and human infants (Homo sapiens) were investigated as to whether they used experimenter-given cues when responding to object-choice tasks. Five conditions were used in different phases: the experimenter tapping on the correct object, gazing plus pointing, gazing closely, gazing alone, and glancing without head orientation. The 3 subject species were able to use all of the experimenter-given cues, in contrast to previous reports of limited use of such cues by monkeys.

Kawai, N. and Matsuzawa, T. (2000) Cognition - Numerical memory span in a chimpanzee. Nature, 403, 39-40.

A female chimpanzee called Ai has learned to use Arabic numerals to represent numbers. She can count from zero to nine items, which she demonstrates by touching the appropriate number on a touch-sensitive monitor, and she can order the numbers from zero to nine in sequence. Here we investigate Ai's memory span by testing her skill in these numerical tasks, and find that she can remember the correct sequence of any five numbers selected from the range zero to nine.

Kitchen, A, Denton, D, Brent, L (1996) Self-recognition and abstraction abilities in the common chimpanzee studied with distorting mirrors . Proceedings of the National Academy of Sciences of the United States of America, Vol.93, No.14, Pp.7405- 7408.

The reactions of chimpanzees to regular mirrors and the results of the standard Gallup mark test have been well documented. In addition to using the mark test to demonstrate self-recognition in a regular mirror, we exposed six female chimpanzees to mirrors that produced distorted or multiplied self-images. Their reactions to their self- images, in terms of mirror-guided self- referenced behaviors, indicated that correct assessment of the source of the mirror image was made by each subject in each of the mirrors. Recognition of a distorted self-image implies an ability for abstraction in the subjects in that the distortion must be rationalized before self- recognition occurs. The implications of these results in terms of illuminating the relative importance of feature and contingency of movement cues to self-recognition are discussed.

Leslie, A.M. (1987) Pretense and representation - the origins of theory of mind. Psychological Review, 94, 412-426

One of the major developments of the second year of human life is the emergence of the ability pretend. A child’s knowledge of a real situation is apparently contradicted and distorted by pretense If, as generally assumed, the child is just beginning to construct a system for internally representing such knowledge, why is this system of representation not undermined by its use in both comprehending ing and producing pretense? In this article I present a theoretical analysis of the representational mechanism underlying this ability. This mechanism extends the power of the infant’s existing capacity for (primary) representation, creating a capacity for metarepresentation. It is this, developing toward the end of infancy, that underlies the child’s new abilities to pretend and to understand pretense in others. There is a striking isomorphism between the three fundamental forms of play and three crucial logical properties of mental state expressions in language. This isomorphism points to a common underlying form of internal representation that is here called metarepresentation tion. A performance model, the decoupler, is outlined embodying ideas about how an infant might compute the complex function postulated to underlie pretend play. This model also reveals pretense as an early manifestation of the ability to understand mental states. Aspects of later school development, both normal and abnormal, are discussed in the light of the new model theory begins the task of characterizing the specific innate basis of our commonsense “theory of mind?.

Limongelli, L, Boysen, ST, Visalberghi, E (1995) Comprehension of cause- effect relations in a tool-using task by chimpanzees (Pan-troglodytes). Journal of Comparative Psychology, Vol.109, No.1, Pp.18-26 Is: 0735-7036.

Five chimpanzees (Pan troglodytes) were tested to assess their understanding of causality in a tool task. The task consisted of a transparent tube with a trap-hole drilled in its middle. A reward was randomly placed on either side of the hole. Depending on which side the chimpanzee inserted the stick into, the candy was either pushed out of the tube or into the trap. In Experiment 1, the success rate of 2 chimpanzees rose highly above chance, but that of the other subjects did not. Results show that the 2 successful chimpanzees selected the correct side for insertion beforehand. Experiment 2 ruled out the possibility that their success was due to a distance- based associative rule, and the results favor an alternative hypothesis that relates success to an understanding of the causal relation between the tool-using action and its outcome.

Menzel, C.R. (1999) Unprompted recall and reporting of hidden objects by a chimpanzee (Pan troglodytes) after extended delays. Journal of Comparative Psychology, 113, 426-434.

The ability to recall features of environments not present to the senses is important in human thinking, planning, and communication, but to date there are almost no data on recall capabilities in nonverbal animals. In this study, the author used symbol knowledge as a tool to study chimpanzee memory. An 11-year-old female chimpanzee (Pan troglodytes) that had already learned a large number of arbitrarily designated geometric forms (lexigrams) watched as an experimenter hid an object in the woods outside her outdoor enclosure. The type and location of the object varied across trials. After an imposed delay of up to 16 h, the chimpanzee could interact indoors with a person who did not know that an object had been hidden, let alone the type or location of the object. A keyboard in the indoor cage displayed 256 lexigrams. From Trial 1, the chimpanzee seemed to do whatever it took to catch the person's attention and then touched the lexigram corresponding to the type of object hidden, pointed outdoors, went outdoors (if followed), and continued to point manually toward the object and vocalize until the person found the object. The subject indicated nonfood objects as well as more than 20 food types.

Menzel, E.W., Savage-Rumbaugh, E.S. and Lawson, J. (1985) Chimpanzee (Pan-troglodytes) spatial problem-solving with the use of mirrors and televised equivalents of mirrors. Journal of Comparative Psychology, 99, 211-217.

Two adult male chimpanzees reached through a hole in the wall of their home cage and, by tracking the images of their hands and of an otherwise hidden target object in a mirror or closed circuit tevelvision picture, moved their hands in whichever direction was necessary to make contact with the target object. They discriminated between live video images and tapes and performed effectively when the target objects were presented in novels locations and when the video picture was presented at random in different orientations. There was thus no consistent relation between the location of images on the monitor and the location of their real-world counterparts. Comparable performances in monkeys and nonprimates seem unlikely.

Mitchell, C.J., Heyes, C.M., Gardner, M.R. and Dawson, G.R. (1999) Limitations of a bidirectional control procedure for the investigation of imitation in rats: Odour cues on the manipulandum. Quarterly Journal of Experimental Psychology Section B- Comparative and Physiological Psychology, 52, 193-202.

Magazine-trained observer rats confronted a conspecific demonstrator pushing a joystick to the right or to the left for food reward before the observers were given access to the joystick from the position previously occupied by the demonstrator and rewarded for responses in both directions. For half of the observers (group 0), the joystick was in the same position when acted upon by demonstrators and observers; for the other half(group 180) the manipulandum was rotated 180 degrees within its mounting between observation and test. As in previous experiments using this bidirectional control procedure, rats in group 0 showed demonstrator-consistent responding-that is, they pushed the joystick in the same direction, relative to the actor's body, as had their demonstrators. However, group 180 showed a reverse effect: reliable demonstrator-inconsistent responding. These results suggest that attractive odour or taste cues deposited by demonstrators on the side of the joystick contralateral to the direction of responding are sufficient to produce demonstrator- consistent responding in the bidirectional control procedure.

Myowa-Yamakoshi, M. and Matsuzawa, T. (1999) Factors influencing imitation of manipulatory actions in chimpanzees (Pan troglodytes). Journal of Comparative Psychology, 113, 128-136.

The purpose of the study was to investigate what kind of factors determine the degree of difficulty for chimpanzees (Pan troglodytes) when they imitate actions. Five adult chimpanzees were instructed to perform 48 arbitrary manipulatory actions consisting of different bodily motor patterns and object directionality. Results showed that actions in which an object is directed toward another external location (another object and one's own body) were easier to perform than those that involved manipulating a single object alone. Actions involving unfamiliar motor patterns were more difficult to perform than those involving familiar motor patterns that were already present in the subject's repertoire. Error responses were characterized as perseverative repetition of previously instructed actions. These findings suggest that chimpanzees find the directionality of manipulated objects a more salient cue than details of the demonstrator's body movements performing the manipulation.

Parr, L.A., Dove, T. and Hopkins, W.D. (1998) Why faces may be special: Evidence of the inversion effect in chimpanzees. Journal of Cognitive Neuroscience, 10, 615-622.

Five chimpanzees were tested on their ability to discriminate faces and automobiles presented in both their upright and inverted orientations. The face stimuli consisted of 30 black and white photographs, 10 each of unfamiliar chimpanzees (Pan troglodytes), brown capuchins (Cebus apella), and humans (Homo sapiens). Ten black and white photographs of automobiles were also used. The stimuli were presented in a sequential matching- to-sample (SMTS) format using a computerized joystick-testing apparatus. Subjects performed better on upright than inverted stimuli in all classes. Performance was significantly better on upright than inverted presentations of chimpanzee and human faces but not on capuchin monkey faces or automobiles. These data support previous studies in humans that suggest the inversion effect occurs for stimuli for which subjects have developed an expertise. Alternative explanations for the inversion effect based on the type of spatial frequency contained in the stimuli are also discussed. These data are the first to provide evidence for the inversion effect using several classes of face stimuli in a great ape species.

Parr, L.A. and de Waal, F.B.M. (1999) Visual kin recognition in chimpanzees. Nature, 399, 647-648.

The ability to distinguish between mem-bers of one's own species has greatly assisted the evolution of sociality in mam-mals, leading to individualized relationships and cooperative networks. Because kin selection is important for the evolution of complex societies, other advantages must derive from the ability to distinguish kin from non-kin. Taking advantage of the chimpanzee's face-recognition abilities and computer skills, we presented five subjects with the task of matching digitized portraits of unfamiliar females with their offspring. We find that chimpanzees can match the faces of mothers and sons, but not mothers and daughters, providing evidence for a mechanism of kin recognition in primates that is independent of previous experience with the individuals in question.

Pepperberg, IM, Garcia, SE, Jackson, EC, Marconi, S (1995) Mirror use by african grey parrots (psittacus-erithacus). Journal of Comparative Psychology, Vol.109, No.2, Pp.182-195.

Two Grey parrots (Psittacus erithacus) were tested on various types of mirror use: mirror image stimulation, mirror-mediated object discrimination, and a simple form of mirror-mediated spatial locating. During exposure to a mirror, neither bird clearly demonstrated self-exploratory behavior but responded instead in ways similar to those of marmosets, monkeys, dolphins, extremely young children (< 18 months), and to the initial responses of orangutans and young chimpanzees. The parrots' behavior was not a consequence of an inability to process mirrored information, because in subsequent tasks they used mirrors to discriminate among exemplars and to locate hidden objects; these birds are the first nonmammalian subjects to exhibit all these behavior patterns. Their behavior on all. the tasks can be compared to that of humans, great apes, dolphins, monkeys, and Asian elephants.

Povinelli, D.J. (1993) Reconstructing the Evolution of Mind. American Psychologist, 48, 493-509.

Since Darwin, the idea of intellectual continuity has gripped comparative psychology. Psychological evolution has been viewed as the accumulation of gradual changes over time, resulting in an unbroken chain of mental capacities throughout the diversity of life. Some researchers have even maintained that no fundamental psychological differences exist among species. An alternative model argues that a rather profound new psychology related to mental state attribution may have evolved recently in the primate order. The author explores recent experimental research from chimpanzees, rhesus monkeys, and children that is consistent with this second model of psychological evolution. Drawing on the fields of developmental, comparative, and social psychology, as well as evolutionary and developmental biology, the author outlines a research agenda aimed at reconstructing the evolution of metacognition.

[not in handout, see intranet]

Povinelli, D.J., Rulf, A.B. and Bierschwale, D.T. (1994) absence of knowledge attribution and self-recognition in young chimpanzees (Pan-troglodytes). Journal of Comparative Psychology, 108, 74-80.

Mirror self-recognition in chimpanzees (Pan troglodytes) is typically delayed until 4½-8 years of age. Also, species capable of mirror self-recognition may be capable of some forms of mental state attribution related to intentions and knowledge. Previous investigations of knowledge attribution by chimpanzees used adolescents and adults but did not explicitly test for self-recognition. We report an investigation of knowledge attribution in 6 young chimpanzees previously tested for self-recognition. Subjects were required to discriminate between a person who had seen where food was hidden and another person who had not. The results are consistent with the proposition that most chimpanzees younger than 4½ years of age show neither mirror self-recognition nor knowledge attribution. The results are also consistent with the idea that, just as in humans, development of self-recognition in chimpanzees may precede development of knowledge attribution.

[not in handout, see intranet]

Povinelli, D.J., Rulf, A.B., Landau, K.R. and Bierschwale, D.T. (1993) Self- recognition in chimpanzees (Pan-troglodytes) - distribution, ontogeny, and patterns of emergence. Journal of Comparative Psychology, 107, 347-372.

Investigations of mirror self-recognition (SR) in chimpanzees (Pan troglodytes) have had small samples and divergent methods. In Experiment 1, 105 chimpanzees (10 months to 40 years of age) were observed for signs of SR across 5 days of continuous mirror exposure. In Experiments 2 and 3, negative SR adult and adolescent chimpanzees were saturated with mirror exposure in efforts to facilitate SR and a longitudinal study was conducted with a number of young subjects. In Experiment 4, mark tests were administered to groups of positive SR, negative SR, and ambiguous SR subjects. In Experiment 5, we explored whether previous positive SR reports in young chimpanzees were artifacts of increased arousal during mirror exposure. Results suggest that SR typically emerges at 4.5-8 years of age, at the population level the capacity declines in adulthood, and in group settings SR typically occurs within minutes of a subject's exposure to a mirror.

Povinelli, DJ, Gallup, GG, Eddy, TJ, Bierschwale, DT, Engstrom, MC, Perilloux, HK, Toxopeus, IB (1997) Chimpanzees recognize themselves in mirrors [full text availability]. Animal Behaviour, Vol.53, No.Pt5, Pp.1083-1088.

Heyes’ (1994, Anim. Behav., 97, 909-919; 1995, Anim. Behav., 50, 1533-1542) recent account of chimpanzees’, Pan troglodytes, reactions to mirrors challenged the view that they are capable of recognizing the equivalence between their mirror images and their physical appearance. In particular, she argued that observations that chimpanzees touch surreptitiously placed marks on their faces while in front of mirrors can be explained as an interaction between ambient levels of face touching and procedural artefacts of the anaesthetization and markings of the subjects. Using new analytical techniques, data are reported that falsify the central predictions generated by her account and confirm predictions derived from the self-recognition model. (C) 1997 The Association for the Study of Animal Behaviour.

Povinelli, DJ, Gallup, GG, Eddy, TJ, Bierschwale, DT, Engstrom, MC, Perilloux, HK, Toxopeus, IB (1997) Chimpanzees recognize themselves in mirrors [full text availability]. Animal Behaviour, Vol.53, No.Pt5, Pp.1083-1088.

Heyes’ (1994, Anim. Behav., 97, 909-919; 1995, Anim. Behav., 50, 1533-1542) recent account of chimpanzees’, Pan troglodytes, reactions to mirrors challenged the view that they are capable of recognizing the equivalence between their mirror images and their physical appearance. In particular, she argued that observations that chimpanzees touch surreptitiously placed marks on their faces while in front of mirrors can be explained as an interaction between ambient levels of face touching and procedural artefacts of the anaesthetization and markings of the subjects. Using new analytical techniques, data are reported that falsify the central predictions generated by her account and confirm predictions derived from the self-recognition model. (C) 1997 The Association for the Study of Animal Behaviour.

Povinelli, DJ, Preuss, TM (1995) Theory of mind - evolutionary history of a cognitive specialization. Trends in Neurosciences, Vol.18, No.9, Pp.418-424.

Traditional analyses of the evolution of intelligence have emphasized commonality and continuity among species. However, recent research suggests that humans might have specialized in a particular kind of intelligence that is related to understanding mental states such as desires, intentions and beliefs. Data indicate that the ability to reflect on one's own mental states, as well as those of others, might be the result of evolutionary changes in the prefrontal cortex. Behavioral studies in children and chimpanzees reveal both similarities and striking differences in the developmental pathways that lead to theory-of-mind capacities. Humans and great apes share many ancient patterns of social behavior, but it is too early to be certain if they interpret them in the same manner. Humans might have evolved a cognitive specialization in theory of mind, forever altering their view of the social universe.

Preuschoft, S (1999) Are primates behaviorists? Formal dominance, cognition, and free-floating rationales. Journal of Comparative Psychology, Vol.113, No.1, Pp.9195.

Contrary to a recent claim (D. Maestripieri, 1996), the concept of formal dominance (F. B. M. de Waal, 1986) is not dependent on higher order intentionality (D. C. Dennett, 1983). Instead, it is implied that primates have a concept of relative dominance and express this relational assessment by contextindependent, unidirectional status indicators. Present evidence supports the view that primates are able to categorize social relationships. In a semiotic framework, a distinction is made between (a) ritualized displays that are symptoms of acute
emotional states (e.g., fear) and (b) formal status indicators that are symbols for a long-term social relationship (e.g., subordination). Criteria to distinguish empirically between these functions relate to species membership and familiarity of interactants, consolidation of relationships, spontaneity of signaling, and specialization of signals.

Ramus, F., Hauser, M.D., Miller, C., Morris, D. and Mehler, J. (2000) Language discrimination by human newborns and by cotton-top tamarin monkeys. Science, 288, 349-351.

Humans, but no other animal, make meaningful use of spoken Language. What is unclear, however, is whether this capacity depends on a unique constellation of perceptual and neurobiological mechanisms or whether a subset of such mechanisms is shared with other organisms, To explore this problem, parallel experiments were conducted on human newborns and cotton-top tamarin monkeys to assess their ability to discriminate unfamiliar Languages. A habituation-dishabituation procedure was used to show that human newborns and tamarins can discriminate sentences from Dutch and Japanese but not if the sentences are played backward. Moreover, the cues for discrimination are not present in backward speech. This suggests that the human newborns' tuning to certain properties of speech relies on general processes of the primate auditory system.

Rendall, D, Seyfarth, RM, Cheney, DL, Owren, MJ (1999) The meaning and function of grunt variants in baboons download full text of article. Animal Behaviour, Vol.57, No.Pt3, Pp.583-592.

Wild baboons, Papio cynocephalus ursinus, give tonal, harmonically rich vocalizations, termed grunts, in at least two distinct, behavioural contexts: when about to embark on a move across an open area ('move' grunts); and when approaching mothers and attempting to inspect or handle their young infants ('infant' grunts). Grunts in these two contexts elicit different responses from receivers and appear to be acoustically distinct (Owren et al. 1997, Journal of the Acoustical Society of America, 101, 2951-2963). Differences in responses to grunts in the two contexts may, then, be due to acoustic differences, reflecting at least a rudimentary capacity for referential signalling. Alternatively, responses may differ simply due to differences in the contexts in which the grunts are being produced. We conducted playback experiments to test between these hypotheses. Experiments were designed to control systematically the effects of both context and acoustic features so as to evaluate the role of each in determining responses to grunts, In playback trials, subjects differentiated between putative move and infant grunts. Their responses based only on the acoustic features of grunts were functionally distinct and mirrored their behaviour to naturally occurring move and infant grunts. However, subjects' responses were in some cases also affected by the context in which grunts were presented, and by an interaction between the context and the acoustic features of the grunts. Furthermore, responses to grunts were affected by the relative rank difference between the caller and the subject. These results indicate that baboon grunts can function in rudimentary referential fashion, but that the context in which grunts are produced and the social identity of callers can also affect recipients' responses. (C) 1999 The Association for the Study of Animal Behaviour.

Russon, AE, Galdikas, BMF (1993) Imitation in free-ranging rehabilitant orangutans (pongo-pygmaeus). Journal of Comparative Psychology, Vol.107, No.2, Pp.147-161.

We made an observational study of spontaneous imitation in orangutans (Pongo pygmaeus). Previous studies may have underestimated great apes' imitative capacities by studying subjects under inhibiting conditions- We used subjects living in enriched environments, namely, rehabilitation. We collected a sample of spontaneous imitations and analyzed the most complex incidents for the likelihood that true imitation, learning new actions by observing rather than by doing, was involved in their acquisition. From 395 hr of observation and other reports on 26 orangutans, we identified 354 incidents of imitation. Of these, 54 complex incidents were difficult to explain by forms of imitation based on associative processes grounded in experiential learning alone; they were, however, congruent with acquisition processes that include true imitation. These findings suggest that orangutans may be capable of true imitation and point to critical eliciting factors.

Sinha, A (1998) Knowledge acquired and decisions made: triadic interactions during allogrooming in wild bonnet macaques, macaca radiata. Philosophical Transactions of the Royal Society of London Series B-Biological Sciences, Vol.353, No.1368, Pp.619- 631.

The pressures of developing and maintaining intricate social relationships may have led to the evolution of enhanced cognitive abilities in many nonhuman primates. Knowledge of the dominance ranks and social relationships of other individuals, in particular, is important in evaluating one's position in the rank hierarchy and affiliative networks. Triadic interactions offer an excellent opportunity to examine whether decisions are taken by individuals on the basis of such knowledge. Allogrooming supplants among wild female bonnet macaques (Macaca radiata) usually involved the subordinate female of a grooming dyad retreating at the approach of a female dominant to both members of the dyad. In a few exceptional cases, however, the dominant member of the dyad retreated; simple noncognitive hypotheses involving dyadic rank differences and agonistic relationships failed to explain this phenomenon. Instead, retreat by the dominant individual was positively correlated with the social attractiveness of her subordinate companion (as measured by the duration of grooming received by the latter from other females in the troop). This suggests that not only does an individual evaluate relationships among other females, but does so on the basis of the amount of grooming received by them. Similarly,the frequency of approaches received by any female was correlated with her social attractiveness when she was the dominant member of the dyad, but not when she was the subordinate. This indicated that approaching females might be aware of the relative dominance ranks of the two allogrooming individuals. In logistic regression analyses, the probability of any individual retreating was found to be influenced more by her knowledge of her rank difference with both the other interactants, rather than by their absolute ranks. Moreover, information about social attractiveness appeared to be used in terms of correlated dominance ranks. The nature of knowledge acquired by bonnet macaque females may thus be egotistical in that other individuals are evaluated relative to oneself, integrative in that information about all other interactants is used simultaneously, and hierarchical in the ability to preferentially use certain categories of knowledge for the storage of related information from other domains.

Spinozzi, G (1993) Development of spontaneous classificatory behavior in chimpanzees (Pan-troglodytes). Journal of Comparative Psychology, Vol.107, No.2, Pp.193-200.

I investigated the development of spontaneous classificatory behavior in 5 chimpanzees (Pan troglodytes) tested at different ages and analyzed subjects' spontaneous constructive interactions with sets of logically structured objects. The results show that chimpanzees possess a natural capacity to react to similarities and differences among test stimuli and construct classes. The general progression of their classificatory development is very similar to that reported for human infants from 6 to 24 months. In both species, classification progresses from constructing single classes by different properties of objects to constructing single classes by similar or identical properties of objects. In addition, like humans, older chimpanzees spontaneously coordinate relations of similarities between sets and construct 2 class-consistent groupings. Chimpanzees' results are compared with those from a similar study with capuchins and macaques.

Thompson, RKR, Oden, DL, Boysen, ST (1997) Language-naive chimpanzees (Pan troglodytes) judge relations between relations in a conceptual matching-to-sample task. Journal of Experimental Psychology-Animal Behavior Processes, Vol.23, No.1, Pp.31-43.

Three chimpanzees with a history of conditional and numeric token training spontaneously matched relations between relations under conditions of nondifferential reinforcement. Heretofore, this conceptual ability was demonstrated only in language-trained chimpanzees. The performance levels of the language-naive animals in this study, however, were equivalent to those of a 4th animal-Sarahwhose history included language training and analogical problem solving. There was no evidence that associative factors mediated successful performance in any of the animals. Prior claims of a profound disparity between language-trained and language- naive chimpanzees apparently can be attributed to prior experience with arbitrary tokens consistently associated with abstract relations and not language per se.

Tomasello, M., Hare, B. and Agnetta, B. (1999) Chimpanzees, Pan troglodytes, follow gaze direction geometrically. Animal Behaviour, 58, 769-777.

Two experiments on chimpanzee gaze following are reported. In the first, chimpanzee subjects watched as a human experimenter looked: around various types of barriers. The subjects looked around each of the barriers more when the human had done so than in a control condition (in which the human looked in another direction). In the second experiment, chimpanzees watched as a human looked towards the back of their cage. As they turned to follow the human's gaze a distracter object was presented. The chimpanzees looked at the distracter while still following the human's gaze to the back of the cage. These two experiments effectively disconfirm the low- level model of chimpanzee gaze following in which it is claimed that upon seeing another animate being's gaze direction chimpanzees simply turn in that direction and look around for something interesting. Rather, they support the hypothesis that chimpanzees follow the gaze direction Of other animate beings geometrically to specific locations, in much the same way as human infants. The degree to which chimpanzees have a mentalistic interpretation of the gaze and/or visual experience of others is still an open question. (C) 1999 The Association for the Study of Animal Behaviour.

Tomasello, M, Call, J, Hare, B (1998) Five primate species follow the visual gaze of conspecifics . Animal Behaviour, Vol.55, No.Pt4, Pp.1063-1069.

Individuals from five primate species were tested experimentally for their ability to follow the visual gaze of conspecifics to an outside object. Subjects were from captive social groups of chimpanzees, Pan troglodytes, sooty mangabeys, Cercocebus atys torquatus, rhesus macaques, Macaca mulatta, stumptail macaques, M. arctoides, and pigtail macaques, M. nemestrina. Experimental trials consisted of an experimenter inducing one individual to look at food being displayed, and then observing the reaction of another individual (the subject) that was looking at that individual (not the food). Control trials consisted of an experimenter displaying the food in an identical manner when the subject was alone. Individuals from all species reliably followed the gaze of conspecifics, looking to the food about 80% of the time in experimental trials, compared with about 20% of the time in control trials. Results are discussed in terms of both the proximate mechanisms that might be involved and the adaptive functions that might be served by gaze-following. (C) 1998 The Association for the Study of Animal Behaviour.

Visalberghi, E, Fragaszy, DM, Savagerumbaugh, S (1995) Performance in a tool-using task by common chimpanzees (pantroglodytes), bonobos (pan-paniscus), an orangutan (pongopygmaeus), and capuchin monkeys (cebus-apella). Journal of Comparative Psychology, Vol.109, No.1, Pp.5260.

Performance by individual animals of three species of great apes (Pan troglodytes, Pan paniscus, and Pongo pygmaeus) and capuchin monkeys (Cebus apella) was assessed by presenting a food treat inside a clear tube. The subjects readily used a straight stick to obtain the food. When sticks were bundled together, the apes immediately unwrapped the bundle to obtain an individual stick, whereas capuchins attempted to insert the bundled sticks. When a misshapen stick was provided, apes, but not capuchins, showed an improvement in terms of modifying the misshapen stick before insertion. Our results indicate that all these species can solve these tasks. However, only the performance of apes is consistent with emerging comprehension of the causal relations required for the avoidance of errors in the more complex tasks.

Walraven, V, Vanelsacker, L, Verheyen, R (1995) Reactions of a group of pygmy chimpanzees (pan-paniscus) to their mirror-images - evidence of self-recognition. Primates, Vol.36, No.1, Pp.145-150.

A group of seven pygmy chimpanzees (Pan paniscus) was tested for their mirror-image reactions during a ten-day experiment. The time spent viewing the mirror waned quickly. Little social responses directed towards the mirror were observed. Self-directed behaviors were shown from testday one on. It was concluded that four out of seven animals could correctly identify their mirror-image, one infant was not (yet) able to do so, and for two other individuals the results were inconclusive.

[not in handout, see intranet]

Whiten, A (1998) Imitation of the sequential structure of actions by chimpanzees(Pan troglodytes). Journal of Comparative Psychology, Vol.112, No.3, Pp.270281.

Imitation was studied experimentally by allowing chimpanzees (Pan troglodytes) to observe alternative patterns of actions for opening a specially designed ''artificial fruit.'' Like problematic foods primates deal with naturally, with the test fruit several defenses had to be removed to gain access to an edible core, but the sequential order and method of defense removal could be systematically varied. Each subject repeatedly observed 1 of 2 alternative techniques for removing each defense and 1 of 2 alternative sequential patterns of defense removal. Imitation of sequential organization emerged after repeated cycles of demonstration and attempts at opening the fruit. Imitation in chimpanzees may thus have some power to produce cultural convergence, counter to the supposition that individual learning processes corrupt copied actions. Imitation of sequential organization was accompanied by imitation of some aspects of the techniques that made up the sequence.

Whiten, A, Custance, DM, Gomez, JC, Teixidor, P, Bard, KA (1996) Imitative learning of artificial fruit processing in children (homo- sapiens) and chimpanzees (Pan- troglodytes). Journal of Comparative Psychology, Vol.110, No.1, Pp.3-14.

Observational learning in chimpanzees and young children was investigated using an artificial fruit designed as an analog of natural foraging problems faced by primates. Each of 3 principal components could be removed in 2 alternative ways, demonstration of only one of which was watched by each subject. This permitted subsequent imitation by subjects to be distinguished from stimulus enhancement. Children aged 2-4 years evidenced imitation for 2 components, but also achieved demonstrated outcomes through their own techniques. Chimpanzees relied even more on their own techniques, but they did imitate elements of 1 component of the task. To our knowledge, this is the first experimental evidence of chimpanzee imitation in a functional task designed to simulate foraging behavior hypothesized to be transmitted culturally in the wild.


Whiten, A., Goodall, J., McGrew, W.C., Nishida, T., Reynolds, V., Sugiyama, Y., Tutin, C.E.G., Wrangham, R.W. and Boesch, C. (1999) Cultures in chimpanzees. Nature, 399, 682-685.

As an increasing number of field studies of chimpanzees (Pan troglodytes) have achieved long-term status across Africa, differences in the behavioural repertoires described have become apparent that suggest there is significant cultural variation(1-7). Here we present a systematic synthesis of this information from the seven most long-term studies, which together have accumulated 151 years of chimpanzee observation. This comprehensive analysis reveals patterns of variation that are far more extensive than have previously been documented for any animal species except humans(8-11). We find that 39 different behaviour patterns, including tool usage, grooming and courtship behaviours, are customary or habitual in some communities but are absent in others where ecological explanations have been discounted. Among mammalian and avian species, cultural variation has previously been identified only for single behaviour patterns, such as the local dialects of song-birds(12,13). The extensive, multiple variations now documented for chimpanzees are thus without parallel. Moreover, the combined repertoire of these behaviour patterns in each chimpanzee community is itself highly distinctive, a phenomenon characteristic of human cultures(14) but previously unrecognised in non-human species.

Wrangham, R.W. Vo (l 42) Evolution of coalitionary killing. Yearbook of Physical Anthropology 1999, 1999, 42, 1-30.

Warfare has traditionally been considered unique to humans. It has, therefore, often been explained as deriving from features that are unique to humans, such as the possession of weapons or the adoption of a patriarchal ideology. Mounting evidence suggests, however, that coalitional killing of adults in neighboring groups also occurs regularly in other species, including wolves and chimpanzees. This implies that selection can favor components of intergroup aggression important to human warfare, including lethal raiding. Here I present the principal adaptive hypothesis for explaining the species distribution of intergroup coalitional killing. This is the "imbalance-of-power hypothesis," which suggests that coalitional killing is the expression of a drive for dominance over neighbors. Two conditions are proposed to be both necessary and sufficient to account for coalitional killing of neighbors: (1) a state of intergroup hostility; (2) sufficient imbalances of power between parties that one party can attack the other with impunity. Under these conditions, it is suggested, selection favors the tendency to hunt and kill. rivals when the costs are sufficiently low. The imbalance-of- power hypothesis has been criticized on a variety of empirical and theoretical grounds which are discussed. To be further tested, studies of the proximate determinants of aggression are needed. However, current evidence supports the hypothesis that selection has favored a hunt-and-kill propensity in chimpanzees and humans, and that coalitional killing has a long history in the evolution of both species. (C) 1999 Wiley-Liss, Inc.

Zuberbuhler, K, Cheney, DL, Seyfarth, RM (1999) Conceptual semantics in a nonhuman primate. Journal of Comparative Psychology, Vol.113, No.1, Pp.3342.

Some animal vocalizations have been described as referential, or semantic, because individuals respond to them as if they designate some object or event. Alternatively, subjects may simply attend to the acoustic features of calls rather than their meanings. Field playback experiments on diana monkeys (Cercopithecus diana diana) tested these hypotheses using the calls of leopards and eagles and the males' alarm calls to these predators. In the experiment, 2 calls were played in sequence, separated by 5 min of silence, such that they were either (a) similar in acoustic and semantic features, (b) similar in semantic features only, or (c) different in both acoustic and semantic features. Subjects readily transferred habituation across acoustic but not semantic features, suggesting that they attended to the calls' underlying meanings.