Performance in a tool-using task by common chimpanzees (Pan troglodytes), bonobos (Pan paniscus), an orangutan (Pongo pygmaeus), and capuchin monkeys (Cebus apella).

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. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The performance of bonobos (Pan paniscus), chimpanzees (Pan troglodytes), and orangutans (Pongo pygmaeus) in two versions of an object-choice task.

The object-choice task tests animals’ ability to use human-given cues to find a hidden reward located in 1 of 2 (or more) containers. Great apes are generally unskillful in this task whereas other species including dogs (Canis familiaris) and goats (Capra hircus) can use human-given cues to locate the reward. However, great apes are typically positioned proximal to the containers when receiving the experimenter’s cue whereas other species are invariably positioned distally. The authors investigated how the position of the subject, the human giving the cue and the containers (and the distance among them) affected the performance of 19 captive great apes. Compared to the proximal condition, the distal condition involved larger distances and, critically, it reduced the potential ambiguity of the cues as well as the strong influence that the sight of the containers may have had when subjects received the cue. Subjects were far more successful in the distal compared to the proximal condition. The authors suggest several possibilities to account for this difference and discuss our findings in relation to previous and future object-choice research. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Scale-model comprehension by chimpanzees (Pan troglodytes).

The ability of chimpanzees (Pan troglodytes) to recognize the correspondence between a scale model and its real-world referent was examined. In Experiments 1 and 2, an adult female and a young adult male watched as an experimenter hid a miniature model food in 1 of 4 sites in a scale model. Then, the chimpanzees were given the opportunity to find the real food item that had been hidden in the analogous location in the real room. The female performed significantly above chance, whereas the male performed at chance level. Experiments 3 and 4 tested 5 adult and 2 adolescent chimpanzees in a similar paradigm, using a scale model of the chimpanzees' outdoor area. Results indicate that some adult chimpanzees were able to reliably demonstrate an understanding of the relationship between a scale model and the larger space it represented, whereas other subjects were constrained by inefficient and unsuccessful search patterns. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Behavioral laterality in captive bonobos (Pan paniscus).

Behavioral laterality was studied in a captive group of 11 bonobos (Pan paniscus). In an observational method a significant left lateral bias in carrying and a right lateral bias in leading limb were found. Direction of lateral bias in carrying and leading limb was enhanced when Ss maintained a bipedal posture. Analysis of bimanual feeding behavior revealed a significant right-hand bias for eating when the Ss were holding food with their left hand. In an experimental method a significant shift toward greater right-hand use was found when Ss were required to maintain a bipedal, rather than a quadrupedal, posture. There was no evidence of lateral bias for measures of face touching, self-touching, or gestures. The results are discussed in the context of previous reports of primate laterality. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Spontaneous classification in action by a human-enculturated and language-reared bonoboo (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. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Memory of movies by chimpanzees (Pan troglodytes).

How do animals remember what they see in daily life? The processes involved in remembering such visual information may be similar to those used in interpreting moving images on a monitor. In Experiment 1, 4 adult chimpanzees (Pan troglodytes) were required to discriminate between movies using a movie-to-movie matching-to-sample task. All chimpanzees demonstrated the ability to discriminate movies from the very 1st session onward. In Experiment 2, the ability to retain a movie was investigated through a matching-to-sample task using movie stills. To test which characteristics of movies are relevant to memory, the authors compared 2 conditions. In the continuous condition, the scenes comprising the movie progressed gradually, whereas in the discrete condition, the authors introduced a sudden change from one scene to another. Chimpanzees showed a recency effect only in the discrete condition, suggesting that composition and temporal order of scenes were used to remember the movies. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Social referencing by young chimpanzees (Pan troglodytes).

Social referencing is the seeking of information from another individual and the use of that information to evaluate a situation. It is a well-documented ability in human infants but has not been studied experimentally in nonhuman primates. Seventeen young nursery-reared chimpanzees (14 to 41 months old) were observed in a standard social referencing paradigm in which they received happy and fear messages concerning novel objects from a familiar human caregiver. Each chimpanzee looked referentially at their caregiver, and the emotional messages that they received differentially influenced their gaze behavior and avoidance of the novel objects. It is concluded that chimpanzees can acquire information about their complex social and physical environments through social referencing and can use emotional information to alter their own behavior. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

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. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Lateral bias in infant chimpanzees (Pan troglodytes).

This study documents the presence, strength, and direction of lateralization in chimpanzees (Pan troglodytes) over the first 3 months of life. Nursery-reared chimpanzees (7 males and 5 females) were repeatedly assessed on a behavioral scale. Lateral bias was measured for 4 behaviors: hand-to-mouth, hand-to-hand, defensive grasp, and first step. Hand-to-mouth was significantly lateralized for the sample. Eight of the 10 chimpanzees that showed hand-to-mouth used the right hand. Lateral bias for defensive grasp was positively related to lateral bias both of first step and of hand-to-mouth. Lateral bias in hand-to-mouth was inversely related to lateral bias in hand-to-hand. Strength of lateralization increased as chimpanzees matured. These laterality effects in infant chimpanzees were expressed under conditions of emotional arousal. Moreover, degree of laterality may be a predictor of responsivity to stress. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Early sensorimotor development in chimpanzees (Pan troglodytes).

Examined the cognitive and locomotor development of 4 chimpanzees (Pan troglodytes) during their 1st yr of life with Piagetian theory and method as paradigm. The infant chimpanzees progressed through the same 4 stages of development as babies do. However, the chimpanzees seemed less developed than babies in object exploration and in object–object combination. When chimpanzee early cognition is compared with that of other nonhuman primates, chimpanzees appear more advanced than gorillas, capuchins, and macaques in these same areas of cognition and similar to orangutans. A unitary explanation of the relative advances and delays in chimpanzee early cognition, which refers to the relation between rates of locomotor and cognitive development, is proposed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Processing of ordinality and transitivity by chimpanzees (Pan troglodytes).

Three chimpanzees (Pan troglodytes) were trained to discriminate among pairs of boxes in an ABCDE-ordered series. The 2nd member of each pair was reinforced, until all 4 training pairs were learned. During novel tests the nonadjacent BD pair was presented, and all 3 animals reliably selected D. In Exp 2, numerals 1–5 served as stimuli. One chimpanzee reliably selected the larger numeral 4 during testing with a nonadjacent pair (2–4), and 2 chimps showed no preference. In a 2nd phase, the same chimp demonstrated proficiency at reversing the task, reliably selecting the smaller of the 2–4 pair. In Exp 4, after additional training, a 2nd test, which included novel test pairs composed of numbers that had not been used during training, was completed. Two of 3 animals were 100% correct on Trial 1 for all novel pairs. The results suggest that chimpanzees with experience in number concepts may recognize the ordinal character of numbers. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A vocabulary test for chimpanzees (Pan troglodytes).

Presented a vocabulary test to 4 cross-fostered chimpanzees (4–6 years old) who had learned some American Sign Language (ASL) in the laboratory. 35 mm color slides were projected on a screen that could be seen by the chimpanzee Ss but not by the human observers. There were 2 observers: 01 was the questioner in the testing room with the Ss; 02 was in a different room. Neither observer could see the other, or the responses of the other observer. 01 and 02 agreed in their readings of both correct and incorrect signs, and most of the signs were the correct ASL names of the slides. To show that the chimpanzees were naming natural language categories—that the sign DOG could refer to any dog, FLOWER to any flower, SHOE to any shoe—each test trial was a 1st trial, in that test slides were presented only once. Analysis of errors showed that 2 aspects of the signs, gestural form and conceptual category, governed the distribution of errors. (64 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Development of self-recognition in chimpanzees (Pan troglodytes).

Chimpanzees demonstrate the ability to recognize themselves in mirrors, yet investigations of the development of self-recognition in chimpanzees are sparse. 12 young chimpanzees, grouped by age, were given mirror exposure and tested for self-recognition and contingent movement. All 6 juveniles, 4 and 5 yrs old, exhibited mirror-guided, mark-directed behavior and clear evidence of self-recognition. In contrast, among the infants, only the oldest group of 2.5-yr-olds exhibited clear evidence of self-recognition. All chimpanzees exhibited both self-directed behaviors and contingent movements. These results suggest that self-recognition occurs at a slightly older age in chimpanzees than in human infants. In humans, self-recognition is linked with other cognitive abilities. The results conform to the general pattern that great apes exhibit many cognitive skills comparable to those of 2-yr-old humans. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

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 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. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Indexical and referential pointing in chimpanzees (Pan troglodytes).

The spontaneous index finger and other referential pointing in 3 adult, laboratory chimpanzees (Pan troglodytes) who have not received language training is reported. Of 256 total observed points, 254 were emitted in the presence of a human to objects in the environment; therefore, the points were communicative. Indicators of intentional communication used by the subjects included attention-getting behaviors, gaze alternation, and persistence until reward. Thus, pointing by these chimpanzees was intentionally communicative. These data imply that perspective-taking and referential communication are generalized hominoid traits, given appropriate eliciting contexts. Index finger pointing was more frequent with the subjects' dominant hands. This study refutes claims that indexical or referential pointing is species-unique to humans or dependent on linguistic competence or explicit training. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

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. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Hand use and gestural communication in chimpanzees (Pan troglodytes).

Hand use in gestural communication was examined in 115 captive chimpanzees (Pan troglodytes). Hand use was measured in subjects while they gestured to food placed out of their reach. The distribution of hand use was examined in relation to sex, age, rearing history, gesture type, and whether the subjects vocalized while gesturing. Overall, significantly more chimpanzees, especially females and adults, gestured with their right than with their left hand. Foods begs were more lateralized to the right hand than pointing, and a greater prevalence of right-hand gesturing was found in subjects who simultaneously vocalized than those who did not. Taken together, these data suggest that referential, intentional communicative behaviors, in the form of gestures, are lateralized to the left hemisphere in chimpanzees. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Transfers of food from adults to infants in tufted capuchins (Cebus apella).

This study examined the behavioral mechanisms that support transfer of food from adults to infants in tufted capuchins (Cebus apella). Two captive groups of capuchins were presented with abundant quantities of unshelled pecans or commercial pellets. Five of 11 infant subjects could not open the nuts. A variety of tolerated interactions were initiated by infants toward adults, and food was frequently transferred. All such interactions were more frequent with nuts (a preferred food) than with pellets. Adult capuchins were equally tolerant of infant capuchins that could open nuts and those that could not. Tolerated interactions during feeding could result in acquisition of dietary information by young capuchins or to important, if intermittent, nutritional support. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Quantity-based interference and symbolic representations in chimpanzees (Pan troglodytes).

Five chimpanzees with training in counting and numerical skills selected between 2 arrays of different amounts of candy or 2 Arabic numerals. A reversed reinforcement contingency was in effect, in which the selected array was removed and the subject received the nonselected candies (or the number of candies represented by the nonselected Arabic numeral). Animals were unable to maximize reward by selecting the smaller array when candies were used as array elements. When Arabic numerals were substituted for the candy arrays, all animals showed an immediate shift to a more optimal response strategy of selecting the smaller numeral, thereby receiving the larger reward. Results suggest that a response disposition to the high-incentive candy stimuli introduced a powerful interference effect on performance, which was effectively overridden by the use of symbolic representations. (PsycINFO Database Record (c) 2010 APA, all rights reserved)