Spontaneous logicomathematical constructions by chimpanzees (Pan troglodytes, P. paniscus)

Two experiments investigated the spontaneous construction of precursory logicomathematical operations by human-enculturated and language-reared chimpanzees (Pan troglodytes, Pan paniscus) when they were interacting freely with objects. In experiment 1, three chimpanzees ranging in age from 6 to 18 years were presented with sets of six objects. Chimpanzees constructed equivalence, order and reversibility relations within single sets of objects as well as between two or three contemporaneous sets of objects. The chimpanzees’ logicomathematical operations were more advanced, including infrequent and minimal operations on three sets, than those of some previously investigated younger nonenculturated common chimpanzees. In experiment 2, six chimpanzees ranging in age from 6 to 21 years were presented with sets of 12 objects. Chimpanzees constructed more advanced operations on single sets, but not on contemporaneous sets. The results suggest partial convergence and partial divergence between development of logicomathematical cognition in chimpanzees and humans. Received: 20 January 1999 / Accepted after revision: 9 August 1999     

Spontaneous spatial constructions by chimpanzees (Pan troglodytes,Pan paniscus)

We investigated chimpanzees’ spontaneous spatial constructions with objects. Two were common chimpanzees ages 6 and 18 years and one was an 11‐year‐old bonobo raised in a very enriched human environment from very early in life. Chimpanzees’ products and procedures were quite advanced when constructing functional spatial relations by placing objects in or on each other, but not when constructing nonfunctional spatial relations by placing objects next to each other. This difference was found in all their constructions, including their spatial correspondences and spatial symmetries. Compared to those of younger nonencultured chimpanzees all their spatial constructions were more advanced. Compared to human infants, their functional spatial constructions were also more advanced but their nonfunctional spatial constructions were less advanced.     

"Constructive" enumeration by chimpanzees (Pan troglodytes) on a computerized task

Two chimpanzees used a joystick to collect dots, one at a time, on a computer monitor (see video-clip in the electronic supplementary material), and then ended a trial when the number of dots collected was equal to the Arabic numeral presented for the trial. Both chimpanzees performed substantially and reliably above chance in collecting a quantity of dots equal to the target numeral, one chimpanzee for the numerals 1–7, and the second chimpanzee for the numerals 1–6. Errors that were made were seldom discrepant from the target by more than one dot quantity, and the perceptual process subitization was ruled out as an explanation for the performance. Additionally, analyses of trial duration data indicated that the chimpanzees were responding based on the numerosity of the constructed set rather than on the basis of temporal cues. The chimpanzees' decreasing performance with successively larger target numerals, however, appeared to be based on a continuous representation of magnitude rather than a discrete representation of number. Therefore, chimpanzee counting in this type of experimental task may be a process that represents magnitudes with scalar variability in that the memory for magnitudes associated with each numeral is imperfect and the variability of responses increases as a function of the numeral's value. Accepted after revision: 11 June 2001 Electronic Publication     

Dominance assertion in male chimpanzees (Pan troglodytes)

The social relations of three adult males in a captive chimpanzee group were evaluated for 12 months. The observations encompassed a period of transition in the dominance hierarchy providing an opportunity to assess behavioral patterns involved in the initiation of status changes. This study shows that dominance in the chimpanzee is expressed primarily through ritualized and non-contact behavior rather than by overt aggression. In particular, display behavior is important for indicating dominance rank, in communicating aggressive intent, and as a prelude to status struggles. The functional relationships between status, displays and other socio-sexual behavior patterns are presented.     

Spontaneous classification in action by a human-enculturated and language-reared bonobo (Pan paniscus) and common chimpanzees (Pan troglodytes).

The authors investigated the formal features of spontaneous manipulations used by 1 bonobo (Pan paniscus) and 2 common chimpanzees (Pan troglodytes) to classify objects in action. Chimpanzees' manipulations were evenly split between serial, one-at-a-time acts on 1 object and parallel, two-at-a-time acts on 2 or 3 objects. Chimpanzees systematically combined their manipulations into routines to generate class-consistent categories of objects. Their routines featured much reproduction of the same manipulations, planful acts that anticipated follow-up manipulations, and manipulations that were reciprocal to each other to accomplish an end. In all these respects, chimpanzees' manipulations were similar to those of 2-year-old human infants. In others they differed. Chimpanzees' routines were mainly based on a linear integration of manipulations. Classifying in action was only infrequently produced by hierarchically integrated routines.     

Chimpanzees (Pan troglodytes) and bonobos (Pan paniscus) quantify split solid objects

Recent research suggests that gorillas’ and orangutans’ object representations survive cohesion violations (e.g., a split of a solid object into two halves), but that their processing of quantities may be affected by them. We assessed chimpanzees’ (Pan troglodytes) and bonobos’ (Pan paniscus) reactions to various fission events in the same series of action tasks modelled after infant studies previously run on gorillas and orangutans (Cacchione and Call in Cognition 116:193–203, 2010b). Results showed that all four non-human great ape species managed to quantify split objects but that their performance varied as a function of the non-cohesiveness produced in the splitting event. Spatial ambiguity and shape invariance had the greatest impact on apes’ ability to represent and quantify objects. Further, we observed species differences with gorillas performing lower than other species. Finally, we detected a substantial age effect, with ape infants below 6 years of age being outperformed by both juvenile/adolescent and adult apes.     

Piagetian conservation of discrete quantities in bonobos (Pan paniscus), chimpanzees (Pan troglodytes), and orangutans (Pongo pygmaeus)

This study investigated whether physical discreteness helps apes to understand the concept of Piagetian conservation (i.e. the invariance of quantities). Subjects were four bonobos, three chimpanzees, and five orangutans. Apes were tested on their ability to conserve discrete/continuous quantities in an over-conservation procedure in which two unequal quantities of edible rewards underwent various transformations in front of subjects. Subjects were examined to determine whether they could track the larger quantity of reward after the transformation. Comparison between the two types of conservation revealed that tests with bonobos supported the discreteness hypothesis. Bonobos, but neither chimpanzees nor orangutans, performed significantly better with discrete quantities than with continuous ones. The results suggest that at least bonobos could benefit from the discreteness of stimuli in their acquisition of conservation skills.     

Strategies used to combine seriated cups by chimpanzees (Pan troglodytes), bonobos (Pan paniscus), and capuchins (Cebus apella).

The authors investigated strategies used to combine seriated cups by apes (Pan troglodytes and P. paniscus) and monkeys (Cebus apella) using a protocol reported in P. M. Greenfield, K. Nelson, and E. Saltzman's (1972) study with children. It was hypothesized that apes would exhibit more hierarchical combinations of cups than monkeys, given apes' language capacity, and that apes would seriate the cups more efficiently than monkeys. As predicted, apes made many structures with the cups using a variety of strategies, and monkeys rarely combined the cups. After a training phase to orient monkeys to the task, the 2 genera did not differ in the strategies used to combine the cups or in efficiency in seriating the cups. Success in this task suggests that sensorimotor versions of hierarchically organized combinatorial activity are well within apes' and monkeys' abilities.     

Structural analysis of tool-use by tufted capuchins (Cebus apella) and chimpanzees (Pan troglodytes)

Using Matsuzawa’s hierarchical system of classification, I compared tool-use patterns of tufted capuchins (Cebus apella) to those of chimpanzees (Pan troglodytes). The results indicated that wild C. apella exhibit fewer and less complex tool-use patterns than do captive C. apella and wild and captive P. troglodytes. Although most patterns of tool-use observed among P. troglodytes occur in captive C. apella, there are some notable exceptions, including tool-use in communicative contexts and the use ¶of three-tool combinations. I conclude that C. apella are unique among monkeys in their demonstrated propensities for higher-order combinatorial behavior and are likely capable of using symbolic combinations, although not at the level of complexity that has been demonstrated in ¶P. troglodytes.     

Spontaneous discrimination of natural stimuli by chimpanzees (Pan troglodytes)

Six chimpanzees (Pan troglodytes) were presented with pairs of color photographic images of 5 different categories of animals (cat, chimp, gorilla, tiger, fish). The subjects responded to each pair using symbols for "same" and "different." Both within- and between-category discriminations were tested, and all chimpanzees classified the image pairs in accordance with the 5 experimenter-defined categories under conditions of nondifferential reinforcement. Although previous studies have demonstrated identification or discrimination of natural categories by nonhuman animals, subjects were typically differentially reinforced for their responses. The present findings demonstrate that chimpanzees can classify natural objects spontaneously and that such classifications may be similar to those that would be observed in human subjects.     

Spontaneous transfer of matching by infant chimpanzees (Pan troglodytes)

Four infant chimpanzees learned a matching-to-sample task when only two training stimuli were used. They then spontaneously transferred the matching concept to novel items, including three-dimensional objects and fabric swatches, without any experimenter-provided differential feedback. These results support the view that the matching concept is broadly construed by chimpanzees from the beginning and does not depend upon explicit training.     

Discrimination and categorization of photographs of natural objects by chimpanzees (Pan troglodytes)

Two experiments assessed the ability of four adult female chimpanzees to categorize natural objects. Chimpanzees were initially trained to match different color photographs of familiar objects from four possible categories. In training, all the comparison stimuli were from the same category in one condition, and from different categories in another condition. For all subjects, training performance was consistently better for the "different category" than for the "same category" trials. Probe trials were shown after training. In probe trials, the sample and positive comparison stimuli were different items from the same category, and the foils were selected from among the three other test categories. Individual performance was above chance in probe trials, suggesting that categorization by chimpanzees may transcend perceptual resemblance. These results were later replicated with novel stimulus items from the same four categories (experiment 2). Altogether, this research demonstrates that chimpanzees grouped perceptually different exemplars within the same category, and further suggests that these animals formed conceptual representations of the categories. Accepted after revision: 10 August 2001 Electronic Publication     

Spontaneous symbol acquisition and communicative use by pygmy chimpanzees (Pan paniscus)

Two pygmy chimpanzees (Pan paniscus) have spontaneously begun to use symbols to communicate with people. In contrast to common chimpanzees (Pan troglodytes) using the same communicative system, the pygmy chimpanzees did not need explicit training in order to form referential symbol-object associations. Instead, they acquired symbols by observing others use these symbols in daily communications with them. In addition, the pygmy chimpanzees have begun to comprehend spoken English words and can readily identify lexigrams upon hearing the spoken words. By contrast, common chimpanzees who received similar exposure to spoken English are unable to do so. The older pygmy chimpanzee has begun to form requests of the form agent-verb-recipient in which he is neither the agent nor the recipient. By contrast, similarly aged common chimpanzees limited their requests to simple verbs, in which the agent was always presumed to be the addressee and the chimpanzee itself was always the recipient, thus they had no need to indicate a specific agent or recipient. These results suggest that these pygmy chimpanzees exhibit symbolic and auditory perceptual skills that are distinctly different from those of common chimpanzees.     

Sequential responding to arabic numerals with wild cards by the chimpanzee (Pan troglodytes)

One adult female chimpanzee (Pan troglodytes) was trained to respond serially to three arabic numerals between 1 and 9, presented on a cathode-ray-tube (CRT) screen. To examine the factors affecting her sequential responding behavior, wild-card items were added to the three-item sequences. When this wild-card item remained until the subject responded to the last numeral (i.e., the terminator condition), her response to the terminator at each point of the sequence was controlled by the ordinal distance between numerals. Thus, the number of responses to the terminator increased as the ordinal distance between numerals increased. When the wild-card item was eliminated by the subject’s response (wild-card conditions), the probability of responses to the wild card before the first numeral increased as a function of the serial position of the first numeral. These results were consistent with previous studies of response time and suggest both serial position and symbolic distance effects. It is suggested that the subject might form the integrated 9-item linear representations by training of possible subsets of three-item sequences. Knowledge concerning the ordinal position of each numeral was established through this training. Received: 27 October 1999 / Accepted: 22 November 1999     

Constructive and deconstructive tool modification by chimpanzees (Pan troglodytes)

Nine chimpanzees (Pan troglodytes) were tested for their ability to assemble or disassemble the appropriate tool to obtain a food reward from two different apparatus. In its deconstructed form, the tool functioned as a probe for one apparatus. In its constructed form, the tool functioned as a hook, appropriate for a second apparatus. Each subject completed four test trials with each apparatus type. Tool types were randomized and counter-balanced between the two forms. Results demonstrated that adult and juvenile chimpanzees (N = 7) were successful with both tool types, while two infant chimpanzees performed near chance. Off-line video analyses revealed that tool modifications followed by attempted solutions by the adults and juveniles were typically correct on the first attempt. Neither infant was successful in modifying tools correctly on the first attempt over all eight trials. The older chimpanzees’ ability to modify the appropriate tool consistently prior to use indicates an immediate recognition of the functional attributes necessary for the successful use of tool types on each apparatus, and represents a non-replication of a previously reported study by Povinelli.

Inferences about guessing and knowing by chimpanzees (Pan troglodytes)

The visual perspective-taking ability of 4 chimpanzees (Pan troglodytes) was investigated. The subjects chose between information about the location of hidden food provided by 2 experimenters who randomly alternated between two roles (the guesser and the knower). The knower baited 1 of 4 obscured cups so that the subjects could watch the process but could not see which of the cups contained the reward. The guesser waited outside the room until the food was hidden. Finally, the knower pointed to the correct cup while the guesser pointed to an incorrect one. The chimpanzees quickly learned to respond to the knower. They also showed transfer to a novel variation of the task, in which the guesser remained inside the room and covered his head while the knower stood next to him and watched a third experimenter bait the cups. The results are consistent with the hypothesis that chimpanzees are capable of modeling the visual perspectives of others.     

Quantity judgments of auditory and visual stimuli by chimpanzees (Pan troglodytes)

Many species can choose between two visual sets of stimuli on the basis of quantity. This is true when sets are both visible, or are presented one set at a time or even one item at a time. However, we know comparatively little about how well nonhuman animals can compare auditory quantities. Here, three chimpanzees (Pan troglodytes) chose between two sets of food items when they only heard each item fall into different containers rather than seeing those items. This method prevented the chimpanzees from summing the amount of visible food they saw because there were no visual cues. Chimpanzees performed well, and their performance matched that of previous experiments with regard to obeying Weber's law. They also performed well with comparisons between a sequentially presented auditory set and a fully visible set, demonstrating that duration of presentation was not being used as a cue. In addition, they accommodated empty sets into these judgments, although not perfectly. Thus, chimpanzees can judge auditory quantities in flexible ways that show many similarities to how they compare visual quantities.     

Tool use by chimpanzees (Pan troglodytes) of the Arnhem Zoo community

Abstract: Chimpanzees have a large repertoire of tool-use behaviors. This study reports on the variety and the extent of tool use exhibited by the chimpanzees of the Arnhem Zoo community in The Netherlands, living in an enriched captive setting since 1971. The use of tools by 29 chimpanzees aged from 0 to 37 years was observed. We identified 13 types of tool use comparable to those found in the wild. Some of these types of tool use seem to be specific to this community, and can be explained by the ecological characteristics of this captive setting. Chimpanzees started to use tools from the age of 2 years. Young chimpanzees, from 5 to 9 years old, showed a greater repertoire of tool use than infants and adults. All types of tool use in the community have appeared by the age of 10, the age of puberty for chimpanzees. Multivariate analysis was applied for the 29 individuals by 13 types of tool use in a one-zero matrix. The results show two major categories of tool use, one in a practical or substantial context and the other in a nonpractical or play context. The subjects clustered into groups reflecting developmental stages, although there are great individual differences. In conclusion, this captive community provides a unique opportunity to clarify the details of tool use by chimpanzees.     

The use of tokens as rewards and tools by chimpanzees (Pan troglodytes)

This paper explores the effectiveness of token rewards in maintaining chimpanzees (Pan troglodytes) in working at intellectually costly tasks, and studies the "saving" behavior of the subjects, investigating the factors that can condition it. Two experiments were run. Tokens were introduced as rewards in a matching-to-sample task and used as exchange tools for food by three adult female chimpanzees. Subjects' performances were maintained at constant high levels of accuracy, suggesting that the tokens were almost equivalent to direct food rewards. The results also showed the emergence of saving behavior. The subjects spontaneously saved the tokens during the matching-to-sample task before exchanging them for food. The chimpanzees also learned a new symbolic discrimination task, with tokens as the reward. During this learning process a rarely reported phenomenon emerged: one of the subjects showed symmetry, a form of stimulus equivalence. Accepted after revision: 7 August 2001 Electronic Publication