Chimpanzee (Pan troglodytes) intentional communication is not contingent upon food

Studies of great apes have revealed that they use manual gestures and other signals to communicate about distal objects. There is also evidence that chimpanzees modify the types of communicative signals they use depending on the attentional state of a human communicative partner. The majority of previous studies have involved chimpanzees requesting food items from a human experimenter. Here, these same communicative behaviors are reported in chimpanzees requesting a tool from a human observer. In this study, captive chimpanzees were found to gesture, vocalize, and display more often when the experimenter had a tool than when she did not. It was also found that chimpanzees responded differentially based on the attentional state of a human experimenter, and when given the wrong tool persisted in their communicative efforts. Implications for the referential and intentional nature of chimpanzee communicative signaling are discussed.     

Differential use of vocal and gestural communication by chimpanzees (Pan troglodytes) in response to the attentional status of a human (Homo sapiens)

This study examined the communicative behavior of 49 captive chimpanzees (Pan troglodytes), particularly their use of vocalizations, manual gestures, and other auditory- or tactile-based behaviors as a means of gaining an inattentive audience's attention. A human (Homo sapiens) experimenter held a banana while oriented either toward or away from the chimpanzee. The chimpanzees' behavior was recorded for 60 s. Chimpanzees emitted vocalizations faster and were more likely to produce vocalizations as their 1st communicative behavior when a human was oriented away from them. Chimpanzees used manual gestures more frequently and faster when the human was oriented toward them. These results replicate the findings of earlier studies on chimpanzee gestural communication and provide new information about the intentional and functional use of their vocalizations.     

Cues that chimpanzees do and do not use to find hidden objects

Chimpanzees follow conspecific and human gaze direction reliably in some situations, but very few chimpanzees reliably use gaze direction or other communicative signals to locate hidden food in the object-choice task. Three studies aimed at exploring factors that affect chimpanzee performance in this task are reported. In the first study, vocalizations and other noises facilitated the performance of some chimpanzees (only a minority). In the second study, various behavioral cues were given in which a human experimenter either touched, approached, or actually lifted and looked under the container where the food was hidden. Each of these cues led to enhanced performance for only a very few individuals. In the third study – a replication with some methodological improvements of a previous experiment – chimpanzees were confronted with two experimenters giving conflicting cues about the location of the hidden food, with one of them (the knower) having witnessed the hiding process and the other (the guesser) not. In the crucial test in which a third experimenter did the hiding, no chimpanzee found the food at above chance levels. Overall, in all three studies, by far the best performers were two individuals who had been raised in infancy by humans. It thus seems that while chimpanzees are very good at “behavior reading” of various sorts, including gaze following, they do not understand the communicative intentions (informative intentions) behind the looking and gesturing of others – with the possible exception of enculturated chimpanzees, who still do not understand the differential significance of looking and gesturing done by people who have different knowledge about states of affairs in the world. Received: 8 November 1999 / Accepted after revision: 24 January 2000     

Olive baboons communicate intentionally by pointing

A pointing gesture creates a referential triangle that incorporates distant objects into the relationship between the signaller and the gesture’s recipient. Pointing was long assumed to be specific to our species. However, recent reports have shown that pointing emerges spontaneously in captive chimpanzees and can be learned by monkeys. Studies have demonstrated that both human children and great apes use manual gestures (e.g. pointing), and visual and vocal signals, to communicate intentionally about out-of-reach objects. Our study looked at how monkeys understand and use their learned pointing behaviour, asking whether it is a conditioned, reinforcement-dependent response or whether monkeys understand it to be a mechanism for manipulating the attention of a partner (e.g. a human). We tested nine baboons that had been trained to exhibit pointing, using operant conditioning. More specifically, we investigated their ability to communicate intentionally about the location of an unreachable food reward in three contexts that differed according to the human partner’s attentional state. In each context, we quantified the frequency of communicative behaviour (auditory and visual signals), including gestures and gaze alternations between the distal food and the human partner. We found that the baboons were able to modulate their manual and visual communicative signals as a function of the experimenter’s attentional state. These findings indicate that monkeys can intentionally produce pointing gestures and understand that a human recipient must be looking at the pointing gesture for them to perform their attention-directing actions. The referential and intentional nature of baboons’ communicative signalling is discussed.     

Apes' use of iconic cues in the object-choice task

In previous studies great apes have shown little ability to locate hidden food using a physical marker placed by a human directly on the target location. In this study, we hypothesized that the perceptual similarity between an iconic cue and the hidden reward (baited container) would help apes to infer the location of the food. In the first two experiments, we found that if an iconic cue is given in addition to a spatial/indexical cue - e.g., picture or replica of a banana placed on the target location - apes (chimpanzees, bonobos, orangutans, gorillas) as a group performed above chance. However, we also found in two further experiments that when iconic cues were given on their own without spatial/indexical information (iconic cue held up by human with no diagnostic spatial/indexical information), the apes were back to chance performance. Our overall conclusion is that although iconic information helps apes in the process of searching hidden food, the poor performance found in the last two experiments is due to apes' lack of understanding of the informative (cooperative) communicative intention of the experimenter.     

Human ostensive signals do not enhance gaze following in chimpanzees,but do enhance object-oriented attention

The previous studies have shown that human infants and domestic dogs follow the gaze of a human agent only when the agent has addressed them ostensively—e.g., by making eye contact, or calling their name. This evidence is interpreted as showing that they expect ostensive signals to precede referential information. The present study tested chimpanzees, one of the closest relatives to humans, in a series of eye-tracking experiments using an experimental design adapted from these previous studies. In the ostension conditions, a human actor made eye contact, called the participant’s name, and then looked at one of two objects. In the control conditions, a salient cue, which differed in each experiment (a colorful object, the actor’s nodding, or an eating action), attracted participants’ attention to the actor’s face, and then the actor looked at the object. Overall, chimpanzees followed the actor’s gaze to the cued object in both ostension and control conditions, and the ostensive signals did not enhance gaze following more than the control attention-getters. However, the ostensive signals enhanced subsequent attention to both target and distractor objects (but not to the actor’s face) more strongly than the control attention-getters—especially in the chimpanzees who had a close relationship with human caregivers. We interpret this as showing that chimpanzees have a simple form of communicative expectations on the basis of ostensive signals, but unlike human infants and dogs, they do not subsequently use the experimenter’s gaze to infer the intended referent. These results may reflect a limitation of non-domesticated species for interpreting humans’ ostensive signals in inter-species communication.     

Great apes infer others’ goals based on context

In previous studies claiming to demonstrate that great apes understand the goals of others, the apes could potentially have been using subtle behavioral cues present during the test to succeed. In the current studies, we ruled out the use of such cues by making the behavior of the experimenter identical in the test phase of both the experimental and control conditions; the only difference was the preceding “context.” In the first study, apes interpreted a human’s ambiguous action as having the underlying goal of opening a box, or not, based on that human’s previous actions with similar boxes. In the second study, chimpanzees learned that when a human stood up she was going to go get food for them, but when a novel, unexpected event happened, they changed their expectation—presumably based on their understanding that this new event led the human to change her goal. These studies suggest that great apes do not need concurrent behavioral cues to infer others’ goals, but can do so from a variety of different types of cues—even cues displaced in time.     

Recent use of signs by chimpanzees (Pan Troglodytes) in interactions with humans

In light of the controversy about the linguistic properties of chimpanzee signing behavior, the recent sign use of 5 chimpanzees (Pan troglodytes) with long histories of sign use was analyzed while they interacted with longtime human companions. Four corpora from 1992 to 1999 consisting of 3,448 sign utterances were examined. The chimpanzees predominantly used object and action signs. There was no evidence for semantic or syntactic structure in combinations of signs. Longer combinations showed repetition and stringing of object and action signs. The chimpanzees mostly signed with an acquisitive motivation. Requests for objects and actions were the predominant communicative intentions of the sign utterances, though naming and answering also occurred. This recent sign use shows multiple differences with (early) human language.     

Should I stay or should I go? Initiation of joint travel in mother–infant dyads of two chimpanzee communities in the wild

It is well established that great apes communicate via intentionally produced, elaborate and flexible gestural means. Yet relatively little is known about the most fundamental steps into this communicative endeavour—communicative exchanges of mother–infant dyads and gestural acquisition; perhaps because the majority of studies concerned captive groups and single communities in the wild only. Here, we report the first systematic, quantitative comparison of communicative interactions of mother–infant dyads in two communities of wild chimpanzees by focusing on a single communicative function: initiation of carries for joint travel. Over 156 days of observation, we recorded 442 actions, 599 cases of intentional gesture production, 51 multi-modal combinations and 80 vocalisations in the Kanyawara community, Kibale National Park, Uganda, and the Taï South community, Taï National Park, Côte d’Ivoire. Our results showed that (1) mothers and infants differed concerning the signal frequency and modality employed to initiate joint travel, (2) concordance rates of mothers’ gestural production were relatively low within but also between communities, (3) infant communicative development is characterised by a shift from mainly vocal to gestural means, and (4) chimpanzee mothers adjusted their signals to the communicative level of their infants. Since neither genetic channelling nor ontogenetic ritualization explains our results satisfactorily, we propose a revised theory of gestural acquisition, social negotiation, in which gestures are the output of social shaping, shared understanding and mutual construction in real time by both interactants.     

Understanding the Point of Chimpanzee Pointing: Epigenesis and Ecological Validity

Abstract— Pointing has long been considered to be a uniquely human, universal, and biologically based gesture. However, pointing emerges spontaneously, without explicit training, in captive chimpanzees. Because pointing is commonplace in captive chimpanzees and virtually absent in wild chimpanzees, and because both captive and wild chimpanzees are sampled from the same gene pool, pointing by captive apes is attributable to environmental influences on communicative development. If pointing by captive chimpanzees is so variably expressed in different rearing environments, this suggests that pointing by humans may also be attributable to situational factors that make pointing effective in certain developmental contexts.     

The Ai project: historical and ecological contexts

This paper aims to review a long-term research project exploring the chimpanzee mind within historical and ecological contexts. The Ai project began in 1978 and was directly inspired by preceding ape-language studies conducted in Western countries. However, in contrast with the latter, it has focused on the perceptual and cognitive capabilities of chimpanzees rather than communicative skills between humans and chimpanzees. In the original setting, a single chimpanzee faced a computer-controlled apparatus and performed various kinds of matching-to-sample discrimination tasks. Questions regarding the chimpanzee mind can be traced back to Wolfgang Koehlers work in the early part of the 20th century. Yet, Japan has its unique natural and cultural background: it is home to an indigenous primate species, the Japanese snow monkey. This fact has contributed to the emergence of two previous projects in the wild led by the late Kinji Imanishi and his students. First, the Koshima monkey project began in 1948 and became famous for its discovery of the cultural propagation of sweet-potato washing behavior. Second, pioneering work in Africa, starting in 1958, aimed to study great apes in their natural habitat. Thanks to the influence of these intellectual ancestors, the present author also undertook the field study of chimpanzees in the wild, focusing on tool manufacture and use. This work has demonstrated the importance of social and ecological perspectives even for the study of the mind. Combining experimental approaches with a field setting, the Ai project continues to explore cognition and behavior in chimpanzees, while its focus has shifted from the study of a single subject toward that of the community as a whole.     

Behavioral cues that great apes use to forage for hidden food

We conducted three studies to examine whether the four great ape species (chimpanzees, bonobos, gorillas, and orangutans) are able to use behavioral experimenter-given cues in an object-choice task. In the subsequent experimental conditions subjects were presented with two eggs, one of which contained food and the other did not. In Study 1 the experimenter examined both eggs by smelling or shaking them, but only made a failed attempt to open (via biting) the egg containing food. In a control condition, the experimenter examined and attempted to open both eggs, but in reverse order to control for stimulus enhancement. The apes significantly preferred the egg that was first examined and then bitten, but had no preference in a baseline condition in which there were no cues. In Study 2, we investigated whether the apes could extend this ability to cues not observed in apes so far (i.e., attempting to pull apart the egg), as well as whether they made this discrimination based on the function of the action the experimenter performed. Subjects significantly preferred eggs presented with this novel cue, but did not prefer eggs presented with a novel but functionally irrelevant action. In Study 3, apes did not interpret human actions as cues to food-location when they already knew that the eggs were empty. Thus, great apes were able to use a variety of experimenter-given cues associated with foraging actions to locate hidden food and thereby were partially sensitive to the general purpose underlying these actions.     

Perceptual biases for multimodal cues in chimpanzee (<Emphasis Type="Italic">Pan troglodytes</Emphasis>) affect recognition

The ability of organisms to discriminate social signals, such as affective displays, using different sensory modalities is important for social communication. However, a major problem for understanding the evolution and integration of multimodal signals is determining how humans and animals attend to different sensory modalities, and these different modalities contribute to the perception and categorization of social signals. Using a matching-to-sample procedure, chimpanzees discriminated videos of conspecifics' facial expressions that contained only auditory or only visual cues by selecting one of two facial expression photographs that matched the expression category represented by the sample. Other videos were edited to contain incongruent sensory cues, i.e., visual features of one expression but auditory features of another. In these cases, subjects were free to select the expression that matched either the auditory or visual modality, whichever was more salient for that expression type. Results showed that chimpanzees were able to discriminate facial expressions using only auditory or visual cues, and when these modalities were mixed. However, in these latter trials, depending on the expression category, clear preferences for either the visual or auditory modality emerged. Pant-hoots and play faces were discriminated preferentially using the auditory modality, while screams were discriminated preferentially using the visual modality. Therefore, depending on the type of expressive display, the auditory and visual modalities were differentially salient in ways that appear consistent with the ethological importance of that display's social function.     

Inferences by exclusion in the great apes: the effect of age and species

This study investigated the ability of chimpanzees, gorillas, orangutans, and bonobos to make inferences by exclusion using the procedure pioneered by Premack and Premack (Cognition 50:347–362, 1994) with chimpanzees. Thirty apes were presented with two different food items (banana vs. grape) on a platform and covered with identical containers. One of the items was removed from the container and placed between the two containers so that subjects could see it. After discarding this item, subjects could select between the two containers. In Experiment 1, apes preferentially selected the container that held the item that the experimenter had not discarded, especially if subjects saw the experimenter remove the item from the container (but without seeing the container empty). Experiment 3 in which the food was removed from one of the containers behind a barrier confirmed these results. In contrast, subjects performed at chance levels when a stimulus (colored plastic chip: Exp. 1; food item: Exp. 2 and Exp. 3) designated the item that had been removed. These results indicated that apes made inferences, not just learned to use a discriminative cue to avoid the empty container. Apes perceived and treated the item discarded by the experimenter as if it were the very one that had been hidden under the container. Results suggested a positive relationship between age and inferential ability independent of memory ability but no species differences.This contribution is part of the special issue “Animal Logics” (Watanabe and Huber 2006).     

Now you see me,now you don't: evidence that chimpanzees understand the role of the eyes in attention

Chimpanzees appear to understand something about the attentional states of others; in the present experiment, we investigated whether they understand that the attentional state of a human is based on eye gaze. In all, 116 adult chimpanzees were offered food by an experimenter who engaged in one of the four experimental manipulations: eyes closed, eyes open, hand over eyes, and hand over mouth. The communicative behavior of the chimpanzees was observed. More visible behaviors were produced when the experimenter's eyes were visible than when the experimenter's eyes were not visible. More vocalizations were produced when the experimenter's eyes were closed than when they were open, but there were no differences in other attention getting behaviors. There was no effect of age or rearing history. The results suggest that chimpanzees use the presence of the eyes as a cue that their visual gestures will be effective.     

Chimpanzees (Pan troglodytes) remember the location of a hidden food item after altering their orientation to a spatial array

Two chimpanzees (Pan troglodytes) had a direct view of an experimenter placing a food item beneath one of several cups within a horizontal spatial array. The chimpanzees then were required to move around the spatial array, shifting their orientation to the array by 180 degrees . Both chimpanzees remembered the location of the food item. In the next experiment, a visual barrier was placed between the chimpanzees and the spatial array after the food item had been hidden to prevent visual tracking of the location of the object during the chimpanzees' movement. One chimpanzee remembered the location of the hidden item in this variation. These results demonstrate another capacity for spatial memory in this species that complements data indicating chimpanzee spatial memory for invisible displacements, array rotations, and array transpositions.     

Chimpanzees (Pan troglodytes) transfer tokens repeatedly with a partner to accumulate rewards in a self-control task

There has been extensive research investigating self-control in humans and nonhuman animals, yet we know surprisingly little about how one’s social environment influences self-control. The present study examined the self-control of chimpanzees in a task that required active engagement with conspecifics. The task consisted of transferring a token back and forth with a partner animal in order to accumulate food rewards, one item per token transfer. Self-control was required because at any point in the trial, either chimpanzee could obtain their accumulated rewards, but doing so discontinued the food accumulation and ended the trial for both individuals. Chimpanzees readily engaged the task and accumulated the majority of available rewards before ending each trial, and they did so across a number of conditions that varied the identity of the partner, the presence/absence of the experimenter, and the means by which they could obtain rewards. A second experiment examined chimpanzees’ self-control when given the choice between immediately available food items and a potentially larger amount of rewards that could be obtained by engaging the token transfer task with a partner. Chimpanzees were flexible in their decision-making in this test, typically choosing the option representing the largest amount of food, even if it involved delayed accumulation of the rewards via the token transfer task. These results demonstrate that chimpanzees can exhibit self-control in situations involving social interactions, and they encourage further research into this important aspect of the self-control scenario.     

The magic cup: great apes and domestic dogs (Canis familiaris) individuate objects according to their properties

Despite current interest in dog (Canis familiaris) cognition, very little is known about how dogs represent objects and how they compare with other species, such as the great apes. Therefore, we investigated how dogs and great apes (chimpanzees [Pan troglodytes], bonobos [Pan paniscus], orangutans [Pongo pygmaeus], gorillas [Gorilla gorilla]) individuate objects in a classical violation of expectation paradigm. We used a container (magic cup) with a double bottom that allowed us to change the type of food that subjects had seen being placed in the container. Using a 2 × 2 design, we varied whether subjects received a generally preferred food and whether the food was substituted (surprise trials) or not (baseline trials). Apes showed increased begging and looking behaviors and dogs showed increased smelling behavior. Both species stayed near the experimenter more frequently in the surprise trials compared with baseline trials. Both species reacted to positive (i.e., good food substituted for bad food) and negative (i.e., bad food substituted for good food) surprises. These results suggest that apes and dogs were able to individuate objects according to their properties or type in comparable ways. In addition, we looked for frustration and elation effects, but subjects' behaviors were not influenced by the food they saw and which they received in previous trials.     

Aping expressions? Chimpanzees produce distinct laugh types when responding to laughter of others

Humans have the ability to replicate the emotional expressions of others even when they undergo different emotions. Such distinct responses of expressions, especially positive expressions, play a central role in everyday social communication of humans and may give the responding individuals important advantages in cooperation and communication. The present work examined laughter in chimpanzees to test whether nonhuman primates also use their expressions in such distinct ways. The approach was first to examine the form and occurrence of laugh replications (laughter after the laughter of others) and spontaneous laughter of chimpanzees during social play and then to test whether their laugh replications represented laugh-elicited laugh responses (laughter triggered by the laughter of others) by using a quantitative method designed to measure responses in natural social settings. The results of this study indicated that chimpanzees produce laugh-elicited laughter that is distinct in form and occurrence from their spontaneous laughter. These findings provide the first empirical evidence that nonhuman primates have the ability to replicate the expressions of others by producing expressions that differ in their underlying emotions and social implications. The data further showed that the laugh-elicited laugh responses of the subjects were closely linked to play maintenance, suggesting that chimpanzees might gain important cooperative and communicative advantages by responding with laughter to the laughter of their social partners. Notably, some chimpanzee groups of this study responded more with laughter than others, an outcome that provides empirical support of a socialization of expressions in great apes similar to that of humans.     

Maintenance of self-imposed delay of gratification by four chimpanzees (Pan troglodytes) and an orangutan (Pongo pygmaeus)

Delay maintenance, which is the continuance over time of the choice to forgo an immediate, less preferred reward for a future, more preferred reward, was examined in 4 chimpanzees (Pan troglodytes) and 1 orangutan (Pongo pygmaeus). In the 1st experiment, the apes were presented with 20 chocolate pieces that were placed, one at a time, into a bowl that was within their reach. The apes could consume the available chocolate pieces at any time during a trial, but no additional pieces would be given. The total length of time taken to place the 20 items into the bowl ranged from 60 s to 180 s. All 5 apes delayed gratification on a majority of trials until all 20 chocolate pieces were presented. Unlike in most experiments with human children using this test situation, attention by the apes to the reward was not detrimental to delay maintenance. In a 2nd experiment with the chimpanzees only, 4 foods of differing incentive value were presented in different trials in the same manner as in Experiment 1. The chimpanzees were highly successful in obtaining all food pieces, and there was no difference in performance as a function of food type.