Naive chimpanzees' (Pan troglodytes) observation of experienced conspecifics in a tool-using task.

The authors investigated the occurrence of naive chimpanzees' (Pan troglodytes) spontaneous observation of experienced conspecifics during a tool-use task entailing honey fishing. The chimpanzees were presented with 20 kinds of "tools" of which 12 kinds were usable. Six pairs of naive and experienced chimpanzees were brought to this honey-fishing situation. A total of 40 observation episodes occurred between the naive and experienced groups, 34 of which were from naive toward experienced individuals. Naive chimpanzees never observed their partners after their own success but did so after their own failure or before their first attempts. In addition, there were 10 cases in which naive individuals used the left-over tools of the experienced ones. Two factors for the transmission of tool use were clearly evident in this study: (a) spontaneous observation of an appropriate behavioral sequence and (b) enhanced environmental cues made by skilled individuals. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Factors influencing imitation of manipulatory actions in chimpanzees (Pan troglodytes).

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. (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)     

Is chimpanzee (Pan troglodytes) spatial attention reflexively triggered by gaze cue?

Humans show a reflexive shift in spatial attention triggered by gaze cues. Chimpanzees (Pan troglodytes) have an excellent ability to follow another's gaze, but they exhibit a limited capacity to engage in triadic interactions based on joint attention, suggesting the possibility of contributions of the different mechanisms underlying joint attention between humans and chimpanzees. The present study thus examined how the chimpanzee's visual spatial attention is triggered by gaze cues. Two chimpanzees showed no clear signs of attention shift triggered by various kinds of nonfacial and facial stimuli with averted gaze under the letter-discrimination tasks but showed significant cueing effects when the head-turning cue was presented in a quasi-dynamic manner. These cueing effects were, however, affected by the predictability of the gaze cue: Highly predictive gaze cues caused stronger cueing effects than less predictive cues. Thus, these results suggest that the shift in spatial attention caused by gaze cues does occur in chimpanzees, but, in contrast to humans, vulnerability against the cue predictability suggests that the voluntary mechanism contributes more dominantly than the reflexive mechanism to this attention shift. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Cardiac correlates of individual recognition in the chimpanzee (Pan troglodytes).

Evaluated the ability of a female chimpanzee (aged 3.5 yrs) to recognize individuals depicted in photographs through the use of heart rate (HR) measures. HR was recorded before and during photographic projections of human caregivers, familiar individuals, strangers, and blank control slides. In the absence of explicit training or reinforcement, the S displayed a differential pattern of HR response to the stimulus categories. Although HR responses to all stimuli were predominantly deceleratory, the photographs of caregivers yielded consistently larger responses than other stimuli. Results indicate that the S was able to recognize individual humans from novel photographic representations and that HR can provide an objective measure than can reflect the social relation between the animal and the individual depicted. (21 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Conspecific recognition in the chimpanzee (Pan troglodytes): Cardiac responses to significant others.

The ability of a chimpanzee (Pan troglodytes) to recognize photographs of conspecifics was evaluated with heart-rate measures. Heart rate was recorded before, during, and after viewing photographs of an aggressive chimpanzee, a friendly companion animal, and an unfamiliar chimpanzee. The subject displayed a differential pattern of heart-rate response to the stimulus animals, without prior experience with the photographs. Responses to the aggressive animal were acceleratory, which suggests a defensive response. Respiratory sinus arrhythmia suggested that this response was associated with sympathetic activation. In contrast, responses to the familiar animal were minimal, whereas cardiac deceleration was observed in response to the strange chimp, which likely reflects an orienting response. Results suggest the chimpanzee is able to recognize photographs of individual conspecifics and that heart-rate change can reflect the nature of established social relationships between chimpanzees. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Absence of knowledge attribution and self-recognition in young chimpanzees (Pan troglodytes).

Mirror self-recognition in chimpanzees is typically delayed until 4.5–8 yrs 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. The authors report an investigation of knowledge attribution in 6 young chimpanzees previously tested for self-recognition. Ss were required to discriminate between a person who had seen where food was hidden and another person who had not. Results are consistent with the proposition that most chimpanzees younger than 4.5 yrs 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. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

How cross-fostered chimpanzees ( Pan troglodytes ) initiate and maintain conversations.

This study systematically sampled typical attention-getting sounds and sign language conversations between each of 4 originally cross-fostered chimpanzees (Pan troglodytes), still living freely, but now in a laboratory setting, and a familiar human interlocutor. Videotape records showed that when they encountered a human interlocutor sitting alone at his desk with his back turned to them, the crossfosterlings either left the scene or made attention-getting sounds. The only signs they made to the interlocutor's back were noisy signs. When the human turned and faced them, the chimpanzees promptly signed to him (98% of the time) and rarely made any sounds during the ensuing signed conversations. Under systematic experimental conditions, the signed responses of the chimpanzees were appropriate to the conversational styles of the human interlocutor, confirming daily field observations. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Manual laterality in chimpanzees (Pan troglodytes) in complex tasks.

To determine the manual laterality of a sample of 24 chimpanzees, 4 problem apparatuses were used, the solution for which (obtaining a food item) required the use of 1 or both hands in sequential, simultaneous, or both sequential and simultaneous actions. The majority of the subjects showed significant and consistent hand preferences, especially in the actions that required a precision grip. The results obtained suggest the existence of factors linked to the specific characteristics of the task to be performed and to the ontogenetic maturation of the subject, which would influence the directionality and degree of the hand preference displayed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Referential Communication by Chimpanzees (Pan troglodytes).

Two experiments were conducted to assess the referential function of chimpanzee (Pan troglodytes) gestures to obtain food. The chimpanzees received 1 trial per condition. In Experiment 1 (N = 101), in full view of the chimpanzee, a banana was placed on top of 1 of 2 inverted buckets or was hidden underneath 1 of the buckets. In Experiment 2 (N = 35), 4 conditions were presented in constant order: (a) no food, no observer; (b) no food, observer present; (c) food present, no observer; and (d) food present, observer present. Gestures and visual orienting were used socially and referentially. The capacity for nonverbal reference may predate the Hominidae-Pongidae split, and the development of nonverbal reference may be independent of human species-specific adaptations for speech. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Summation in the chimpanzee (Pan troglodytes).

In this research, we asked whether 2 chimpanzee (Pan troglodytes) subjects could reliably sum across pairs of quantities to select the greater total. Subjects were allowed to choose between two trays of chocolates. Each tray contained two food wells. To select the tray containing the greater number of chocolates, it was necessary to sum the contents of the food wells on each tray. In experiments where food wells contained from zero to four chocolates, the chimpanzees chose the greater value of the summed wells on more than 90% of the trials. In the final experiment, the maximum number of chocolates assigned to a food well was increased to five. Choice of the tray containing the greater sum still remained above 90%. In all experiments, subjects reliably chose the greater sum, even though on many trials a food well on the "incorrect" tray held more chocolates than either single well on the "correct" tray. It was concluded that without any known ability to count, these chimpanzees used some process of summation to combine spatially separated quantities. (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)     

Numerical judgments by chimpanzees (Pan troglodytes) in a token economy.

We presented four chimpanzees with a series of tasks that involved comparing two token sets or comparing a token set to a quantity of food. Selected tokens could be exchanged for food items on a one-to-one basis. Chimpanzees successfully selected the larger numerical set for comparisons of 1 to 5 items when both sets were visible and when sets were presented through one-by-one addition of tokens into two opaque containers. Two of four chimpanzees used the number of tokens and food items to guide responding in all conditions, rather than relying on token color, size, total amount, or duration of set presentation. These results demonstrate that judgments of simultaneous and sequential sets of stimuli are made by some chimpanzees on the basis of the numerousness of sets rather than other non-numerical dimensions. The tokens were treated as equivalent to food items on the basis of their numerousness, and the chimpanzees maximized reward by choosing the larger number of items in all situations. (PsycINFO Database Record (c) 2011 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)     

Numerical competence in a chimpanzee (Pan troglodytes).

A chimpanzee (Pan troglodytes), trained to count foods and objects by using Arabic numbers, demonstrated the ability to sum arrays of 0–4 food items placed in 2 of 3 possible sites. To address representational use of numbers, we next baited sites with Arabic numbers as stimuli. In both cases performance was significantly above chance from the first sessions, which suggests that without explicit training in combining arrays, the animal was able to select the correct arithmetic sum for arrays of foods or Arabic numbers under novel test conditions. These findings demonstrate that counting strategies and the representational use of numbers lie within the cognitive domain of the chimpanzee and compare favorably with the spontaneous use of addition algorithms demonstrated in preschool children. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Chimpanzees (Pan troglodytes) conceal visual and auditory information from others.

Chimpanzees (Pan troglodytes) competed with a human for food. The human sat inside a booth, with 1 piece of food to her left and 1 to her right, which she could retract from her chimpanzee competitor's reach as needed. In Experiment 1, chimpanzees could approach either side of the booth unseen but then had to reach through 1 of 2 tunnels (1 clear, 1 opaque) for the food. In Experiment 2, both tunnels were clear and the human was looking away, but 1 of the tunnels made a loud noise when it was opened. Chimpanzees preferentially reached through the opaque tunnel in the first study and the silent tunnel in the second, successfully concealing their taking of the food from the human competitor in both cases. These results suggest that chimpanzees can, in some circumstances, actively manipulate the visual and auditory perception of others by concealing information from them. (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)     

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)     

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)